HK1228101A1 - Methods, apparatus, and system for mass spectrometry - Google Patents

Description

Method, device and system for mass spectrometry

The present application is a divisional application of a patent application entitled "method, apparatus and system for mass spectrometry" filed on 14/2/2012, 2012 and filed under application No. 201280018473.3(PCT/US 2012/025032).

Cross reference to related patent applications

This application claims the benefit of U.S. provisional patent application No.61/442,385 entitled Mass Spectrometer, filed on day 14/2/2011, which is hereby incorporated by reference.

The present application also claims the benefit of U.S. provisional patent application No.61/565,763 entitled "a Structurally Robust Miniature Mass spectrometer comprising Self-Aligning Ion Optics" filed on 12/1/2011, which is hereby incorporated by reference.

Background

Mass spectrometry is one of the leading chemical analysis tools. A mass spectrometer, which is often used in conjunction with another instrument (e.g., gas chromatography) as a detector, may be capable of determining the relative abundance (relative abundance) of a chemical species present in a gaseous sample by separating the chemical species by atomic mass.

Mass spectrometry is widely used in numerous disciplines. The mass spectrometer has been sent to the unmanned spacecraft; both sea theft landers (Viking landers) carry a Gas Chromatograph Mass Spectrometer (GCMS) package, and the casini-Huygens (Cassini-Huygens) probe that falls into the earth's hexaatmospheric layer also carries GCMS. Mass spectrometers are used extensively in bioscience; they are one of the commonly used methods for determining protein structure and sequence.

In the medical field of pharmacokinetics, mass spectrometers have been used to track minute quantities of drugs through the human body.

Mass spectrometers have been designed for chemical and biological defense; the second group of chemical-biological mass spectrometers (CBMS) is designed as portable on-board instruments that are capable of detecting chemical and biological threats in the field (e.g., nerve agents, bacteria). More recently, mass spectrometers have been loaded on unmanned submersibles to aid in tracking hydrocarbons released by Macondo (Macondo) well failures in the gulf of mexico on 4 months and 20 days 2010.

Mass spectrometers have also been used in many other fields. As early as 1976, mass spectrometers were used to constantly analyze the gas breathed by patients wearing ventilators in intensive care to prevent potentially dangerous complications.

Disclosure of Invention

The applicant has realised that a conventional mass spectrometer is an extremely versatile instrument, but it is not without some drawbacks. Conventional mass spectrometers are typically large, complex and expensive instruments that may consume a significant amount of electrical power.

In view of the foregoing, embodiments of the invention disclosed herein are directed, in part, to an improved mass spectrometer that can be small enough to be hand-held, capable of operating at minimal power for a useful period of time in remote use, and inexpensive enough to build and assemble so that it can be widely deployed. The illustrative instruments can be deployed in large numbers to cover a wide area for air or water quality monitoring, installed in industrial exhaust stacks for combustion process feedback control, or attached to hospital ventilators, or used as primary response tools in emergency rooms.

Embodiments of the invention include mass spectrometers and corresponding methods of mass spectrometry. One illustrative mass spectrometer includes a vacuum enclosure defining a support of about 10^-5A vacuum chamber of mm Hg or less, and electrodes and a switching circuit disposed in the vacuum chamber. Feedthroughs having a dielectric strength of about 36V or less than 36V provide electricity between the conversion circuitry and a power source external to the vacuum chamberAnd (4) connecting. In some examples, the feedthrough may provide the only electrical connection between the interior of the vacuum chamber and the exterior of the vacuum chamber. The conversion circuit receives an input voltage (e.g., at a first value of about 1V to about 36V) from the power source via the feedthrough and converts the input voltage to an electrode potential (e.g., at a second value of about 100V to about 5kV) and charges the electrode to the electrode potential. The electrode controls acceleration of charged particles propagating through the vacuum chamber once the electrode is charged to the electrode potential.

In one example, the charged particles are electrons. In such an example, the mass spectrometer may further comprise: an electron source disposed in the vacuum chamber to provide the electrons; a cathode for repelling the electrons; and an anode disposed on a side of the control electrode opposite the electron source to accelerate the electrons toward particles to be analyzed. The conversion circuit may be configured to provide: an anode potential of about 100V to about 5kV for the anode; a cathode potential for the cathode of about 70V below the anode potential; and the electrode potential is about 0V to about 140V below the anode potential.

Such mass spectrometers can also include electronics (e.g., a microprocessor, analog-to-digital converter, or digital-to-analog converter) disposed in the vacuum chamber to control or vary the electrode potentials (e.g., control the acceleration of the electrons). The electronics can also be coupled to a detector that determines a mass of the charged particles from the acceleration of the charged particles.

Another illustrative mass spectrometer and corresponding method of mass spectrometry includes a magnet in a yoke for generating a magnetic field having a first strength (e.g., about 0.1T) in a first region and a second strength (e.g., about 0.7T) in a second region. It also includes a vacuum enclosure defining a vacuum chamber, an ion pump disposed in the first region to maintain a vacuum pressure of the vacuum chamber, and a mass analyzer (e.g., a sector magnetic analyzer) disposed in the second region to determine a mass of particles propagating through the vacuum chamber. Control electrodes disposed in the vacuum chamber control the acceleration of electrons ionizing the particles, and switching circuitry disposed in the vacuum chamber provides one or more voltages to the ion pump, the electrodes, and/or the mass analyzer.

Another example of the illustrative mass spectrometer may include control electronics disposed in the vacuum chamber and in electrical communication with the control electrode to vary the potential of the control electrode. It may also include signal processing electronics disposed in the vacuum chamber and powered by the conversion circuitry to process the signal provided by the mass analyzer.

Such mass spectrometers can also include: an electron source disposed in the vacuum chamber to provide the electrons; a cathode shielding the electron source from the vacuum chamber; and an anode disposed on a side of the control electrode opposite the electron source to accelerate the electrons toward particles to be analyzed. The switching circuit may be configured to provide an anode potential of about 100V to about 5kV for the anode, a cathode potential of about 70V below the anode potential for the cathode, and the electrode potential, which may be about 0V and about 140V below the anode potential. Further, the switching circuit may be configured to boost the input voltage with a first value of about 1V to about 36V to the electrode potential at a second value of about 100V to about 5 kV.

It should be understood that all combinations of the above concepts and further concepts discussed in greater detail below (which concepts are not mutually inconsistent) are considered to be part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are considered part of the inventive subject matter disclosed herein. It is also to be understood that the terminology explicitly used herein that may also be found in any disclosure contained by reference should be accorded a meaning that is nearly consistent with the specific concepts disclosed herein.

Drawings

Skilled artisans will appreciate that the figures are primarily for illustrative purposes and are not intended to limit the scope of the inventive subject matter described herein. The drawings are not necessarily to scale; in some instances, aspects of the inventive subject matter disclosed herein may be shown exaggerated or enlarged in the drawings to help understand various features. In the drawings, like reference numbers generally indicate like features (e.g., functionally similar and/or structurally similar elements).

FIG. 1A is a computer-aided design (CAD) model of an exemplary mass spectrometer according to an embodiment of the present invention.

FIG. 1B is a diagram of a low dielectric strength feedthrough suitable for use with the mass spectrometer of FIG. 1A, in accordance with an embodiment of the invention.

FIG. 1C shows a CAD model of the yoke of FIG. 1A, in accordance with embodiments of the present invention.

Fig. 1D shows a Computer Aided Design (CAD) model of a magnetic yoke in combination with a pair of permanent magnets, an ion pump, and a mass analyzer, according to another embodiment of the invention.

Figure 2 is a graph of ion source potential versus ion mass for a mass spectrometer according to an embodiment of the present invention.

Fig. 3 is a diagram of an optical device suitable for use in an ion source according to an embodiment of the present invention.

FIG. 4 is a schematic diagram of a mass spectrometer with a discrete dynode electron multiplier and an electrometer detector according to an embodiment of the invention.

FIG. 5 is a cross-sectional view of a membrane inlet to the atmosphere according to an embodiment of the invention.

Fig. 6A is a simulation of an ion analyzer according to an embodiment of the present invention.

Figure 6B is a SIMION simulation of carbon dioxide molecules passing through a miniature mass spectrometer according to an embodiment of the present invention.

Fig. 6C is a view of an ion source and a first ion lens according to an embodiment of the invention.

Figure 7 is an isometric view of potential energy distributions in a mass spectrometer ion source and analyzer in accordance with an embodiment of the present invention. The curvature of the green potential surface represents the effect of an electrostatic lens. The vertical dimension is the potential energy and the two horizontal dimensions are the planar shapes of the mass spectrometer.

Fig. 8 is a side cross-sectional view of a SIMION simulation of a cylindrical pierce diode ion source according to an embodiment of the present invention. Electrons are emitted from the surface of the filament in a line. A cathode potential electrode surrounds the filament to shield it from the vacuum chamber. The gate and anode electrodes are shown at the right edge of the simulation.

Fig. 9 is a side cross-sectional view of the cylindrical pierce diode ion source of fig. 8 with a control electrode biased to suppress electron emission in accordance with an embodiment of the invention.

Fig. 10 is a CAD layout of a printed circuit board substrate positioned below a mass spectrometer according to an embodiment of the invention.

FIG. 11 is a CAD layout illustrating a mass spectrometer according to an embodiment of the invention.

Fig. 12 is a CAD model of an exemplary mass analyzer electrode with a slit mounted on a flexure according to an embodiment of the invention.

FIG. 13 is a schematic view of an adjustable flexure according to an embodiment of the present invention.

Fig. 14 includes a photograph of an electrode cut from a stainless steel plate by wire EDM (left) and a photograph of an electrode etched in nitric acid to remove an oxide layer (left) according to an embodiment of the present invention.

Fig. 15 is a CAD model of an anode of a compact ion pump according to an embodiment of the invention.

FIG. 16 is a photograph illustrating a mass spectrometer with the top cover and yoke removed, according to an embodiment of the invention.

Fig. 17 is a photograph illustrating adjustment of an entrance slit to the illustrative mass analyzer of fig. 16, in accordance with an embodiment of the present invention.

Fig. 18A is a photograph of an assembled mass spectrometer attached to a confrat (coneflat) flange for testing according to an embodiment of the invention.

Figure 18B is a photograph of a vacuum chamber used in the development of a mass spectrometer according to an embodiment of the present invention. The ion gauge is on the left and the turbo pump is on the bottom.

Figure 19 is a block diagram of a digital controller for a mass spectrometer according to an embodiment of the present invention.

FIG. 20 is a perspective view of a substrate with a outgassing heater according to an embodiment of the invention.

FIG. 21 is a graph of vacuum chamber pressure versus time with heater transition indications for an illustrative mass spectrometer according to an embodiment of the present invention.

FIG. 22 shows thermal images of an analyzer plate obtained at 0s, 10s, 20s, 60s, 300s, and 600s after heater activation, according to an embodiment of the present invention; the heat range is 30 ℃ (black) to 60 ℃ (white).

FIG. 23 is a graph illustrating the relationship of microprocessor command voltage to the actual output of each lens driver for a mass spectrometer according to an embodiment of the invention.

FIG. 24 is a graph illustrating system pressure, ion pump voltage, and ion pump current versus time for a mass spectrometer according to an embodiment of the invention.

FIG. 25 is a graph of system pressure, ion pump voltage, and ion pump current for minutes after vacuum system split for an illustrative mass spectrometer according to an embodiment of the invention.

Fig. 26 is a photograph of a plate of a disassembled ion pump according to an embodiment of the present invention; the colored deposit may be chromium from a stainless steel anode.

FIG. 27 is a mass spectrum captured by an illustrative mass spectrometer according to an embodiment of the invention.

FIG. 28 is a mass spectrum of air captured by another illustrative mass spectrometer according to an embodiment of the invention.

Fig. 29 is a mass spectrum diagram showing values of a large part of ions generated by an electron beam captured and used by an electrostatic lens having an active electrostatic lens (upper curve) and a disabled electrostatic lens (lower curve).

Fig. 30 is a mass spectrum diagram showing the effect of narrowing a slit that filters an ion beam according to an embodiment of the present invention. Peaks such as m/z 27 and 26 are not visible with wider slits (lower curve), but are easily visible with narrow slits (upper curve).

FIG. 31 is a graph showing the detection of a new species, nitrous oxide or N, using an illustrative mass spectrometer according to an embodiment of the present invention₂And the mass spectrogram of O and a fragmentary component NO thereof.

FIG. 32 is a mass spectrum captured using the electron source grid (control electrode) of a mass spectrometer to generate a signal that can be subtracted from the signal to eliminate electrometer offset and drift traces.

Detailed Description

The following is a more detailed description of various concepts and embodiments related to the systems, methods and apparatus for mass spectrometry of the present invention. It should be appreciated that the various concepts introduced above and discussed in greater detail below may be implemented in any of numerous ways, as the disclosed concepts are not limited to any particular implementation. Examples of specific implementations and applications are provided primarily for illustrative purposes.

1.0 overview of Mass Spectrometry

Many different implementations of mass spectrometers exist and the configuration generally depends on the desired application. However, they typically include the same basic functional blocks: an inlet, an ion source, a mass analyzer, a detector, and a vacuum system. The sample entering the inlet is ionized, typically by bombardment with an electron beam, then separated by mass with one or more electric and/or magnetic fields, and then analyzed for relative abundance.

Finally, all implementations of mass spectrometers generate a graph that relates the atomic mass-to-charge (m/z) ratio of the components of the sample being ionized to the relative abundance of each component. For example, a mass spectrometer measuring an atmospheric sample will find components of masses 28, 32, 40 and 44, and possibly other masses depending on the sensitivity of the instrument. These masses correspond to nitrogen, oxygen, argon and carbon dioxide. The mass spectrometer output will show the highest signal intensity for nitrogen of mass 28, constituting 70% of the atmospheric gas, then about 1/3 for the nitrogen peak for oxygen of mass 32 (22% of the atmosphere), and lower for argon and carbon dioxide.

Depending on the application, mass spectrometers are typically designed for a particular mass range and resolution. The mass range may be 10 to 50AMU for instruments designed for ambient gas monitoring, or tens of thousands of AMU for instruments used in protein analysis. Mass spectrometers often scan this mass range through by varying one of the electric or magnetic field parameters to produce spectra with mass-to-charge (m/z) ratios and time (undesirably). This scan will produce a peak in signal strength where mass is present. The resolution of the mass spectrometer is determined by how narrow these peaks are; some mass spectrometers can only resolve a unit mass, while some can resolve very small fractions of the mass (e.g., to distinguish between different species present at the same nominal unit mass, such as carbon monoxide at 28.010 and nitrogen at 28.0134). Peaks are generally characterized by full-width half-maximum (FWHM) measurements; the width of the peak at half the peak amplitude can help determine which masses will be visible. Generally, mass spectrometers that produce narrower peaks have better resolving power than those with broad peaks.

FIG. 1A shows an isometric view of a computer-aided design (CAD) model of an example mass spectrometer 100, which is shown without a vacuum enclosure for illustrative purposes. Unless otherwise noted, the assembly shown in fig. 1A is located in a vacuum chamber defined by a vacuum housing and a vacuum flange 170. The vacuum enclosure seal 172, which extends along the surface of the vacuum flange, prevents leakage, which allows the vacuum pressure to reach le-5 torr (torr) or less. An inlet 180 extends through the vacuum flange 170 to allow introduction of a sample for analysis.

Mass spectrometer 100 includes shared magnetic circuit 110, shared magnetic circuit 110 being formed by one or more magnets 112 within a magnetic yoke 114. The yoke 140 couples magnetic flux from the magnet 112 into the two or more magnetic field regions 111a and 111 b. The ion pump (shown as integrated ion pump electrode 120 in fig. 1A) within the first region 111A maintains a vacuum pressure within the vacuum chamber, and the fan-shaped magnetic mass analyzer 130 in the second region 111b separates the ionized sample particles according to mass, as is known in the art. The ion source 104 generates ions by ionizing particles entering through the inlet 180 with electrons from an electron source (not shown), which are collimated by the ion optics 300. An ion detector 140 at one end of the magnetic mass analyzer 130 generates a current that varies with the number of ions collected by the detector 140.

The mass analyzer 130 and the ion detector 140 are mounted on a planar substrate 190, the planar substrate 190 can be made of Printed Circuit Board (PCB) material as described below, the planar substrate 190 also supporting the conversion circuit (high voltage power supply) 150. The base plate 190 is mounted to the vacuum flange 170 via the yoke 114. Those having ordinary skill in the art will readily appreciate that other mounting configurations are possible.

The switching circuit 150 switches or increases an input voltage from an external power supply having about 1-36V (e.g., 12V) to a sufficiently high voltage (e.g., 100V to 5kV) to charge electrodes within the vacuum chamber, including any electrodes in the electron source, ion source 104, ion optics 300, and ion detector 140. The conversion circuit 150 may be coupled to an external power source via a single feedthrough (not shown) having a relatively low dielectric strength (e.g., a dielectric strength equal to or less than about 36V or less, equal to or less than about 24V, equal to or less than about 12V, or equal to or less than about 9V). In at least one embodiment, this low dielectric strength feedthrough is the only electrical connection between the interior and exterior of the vacuum chamber defined by the vacuum flange 170 and the vacuum enclosure (not shown).

Fig. 1B illustrates a low dielectric strength feedthrough 174 suitable for use with the conversion circuit 150, vacuum enclosure, and vacuum flange 170 of fig. 1A. Such low dielectric strength feedthroughs 174 can be quickly and inexpensively made of epoxy, and can have a dielectric strength equal to or less than about 36V or less. To fabricate this feedthrough 174, a small hole is drilled through the vacuum housing (e.g., through the vacuum flange 170), which tapers to a diameter toward the vacuum side just large enough to accept a feedthrough wire 178, which may be bare or coated with a conformal insulating layer (e.g., a magnet wire). The wire 178 is placed and the hole is backfilled with a low outgassing epoxy to form an epoxy seal or plug 176. In this configuration, the epoxy plug 176 encounters a small force; since the hole is primarily filled by the wire 178 and the epoxy 176 holds the wire 178 in place, the vacuum flange 170 or housing still carries the compliance. The use of bare or conformally coated wires reduces the variation of vacuum leakage between the wires 178 and their insulating layers that can occur with wires insulated by a separate jacket.

Since even the most efficient conversion circuit 150 dissipates energy in the form of heat, it is counterintuitive to place the conversion circuit 150 within a vacuum chamber. The heat raises the temperature of other components of the chamber, including the substrate 190. As the other components heat up, they may release the absorbed or adsorbed gas, which causes the pressure inside the chamber to rise, increasing the load on the ion pump 120.

However, placing the conversion circuit 150 within a vacuum chamber makes it possible to eliminate high voltage electrical feedthroughs, which are often expensive and difficult to manufacture. Unlike low dielectric strength feedthroughs, high voltage electrical feedthroughs typically need to provide vacuum-tight electrical connections that can withstand hundreds or thousands of volts relative to the vacuum enclosure and can be baked out at hundreds of degrees celsius. They are typically made of Kovar (Kovar) and brazed to a ceramic dielectric which is then brazed to a stainless steel housing or fitting.

2.0 type of Mass spectrometer

There are many different types of mass spectrometers, which are generally divided by the method used to separate the different masses. This section briefly covers some of the simpler types of mass spectrometers and, although far from being nearly comprehensive, describes those types that are possible to be manufactured inexpensively.

2.1 types of Mass Analyzers

A magnetic sector mass spectrometer (e.g., mass analyzer 130 shown in fig. 1A) produces a spatial separation of masses. In this design, the ionized sample is accelerated in an electric field and injected into a region with a perpendicular magnetic field. The radius of curvature of the trajectory of an ion in a magnetic field is proportional to its mass and inversely proportional to its charge state. By scanning the electric field and thus changing the kinetic energy of the ions or by scanning the magnetic field and changing the trajectory of the ions, the various masses can be separated and detected independently. There are many variations of this design, including having separate or combined electric or magnetic field portions that produce improved resolution.

Time-of-flight mass spectrometers are another design that produces a temporal separation of masses. Implanting ions into the drift region by a fixed electric field; the separation in final ion velocity, and hence the time to reach the far end of the drift region, is proportional to the ion mass.

Quadrupole mass spectrometers use two pairs of electrodes parallel to the ion flight path; by applying a variable frequency RF field using one pair of electrodes and a DC bias on the other pair of electrodes, and adjusting the RF field for a particular mass, only one mass has a stable trajectory through each field at any particular time.

A similar mass spectrometer, an "ion trap mass spectrometer", uses a principle similar to a quadrupole mass spectrometer to capture a volume of ion cloud and selectively destabilize the orbit of a particular mass. Then, an unstable mass is emitted from the ion volume and measured.

2.2 ion Source

Mass analyzers typically rely on ionized samples injected into the mass analyzer for proper operation. Once the sample is ionized, the ionized sample molecules (ions) can be manipulated and separated by the electromagnetic field.

A common ion source uses electron ionization. In such sources, an electron beam, typically thermionically generated, is aimed into the gas sample. Electrons that interact with sample molecules remove electrons from the sample, producing positively charged sample ions, but for some electronegative chemical species, negative ion mass spectrometers are practical.

2.3 Detector

Once the sample has been ionized and the generated ions separated by mass, the ions can be detected with a detector (e.g., detector 140 in fig. 1A). The simplest detector is a faraday cup followed by a high gain transconductance amplifier. Ions striking the faraday cup produce a small but measurable current which is then amplified and recorded. However, since these detectors do not provide intrinsic gain, the noise floor (noise floor) is the noise floor of the amplifier.

3.0 Mass spectrometer design overview

Illustrative embodiments of the miniature mass spectrometer disclosed herein can have a simple, robust design that can be manufactured without the use of complex or labor intensive manufacturing techniques. Each design choice may involve a tradeoff between a number of factors, among which performance, size, weight, power consumption, complexity, ease of manufacture, and cost. Such a design may be manufacturable using automated tooling. Manufacturing can be further simplified by creating a planar design that relies on two-dimensional (2D) machining; any feature in the third dimension can be established or approximated by stacking multiple layers of the 2D processed component. Eliminating secondary machining operations can help eliminate extra clamping (fixturing), time, and waste. Thus, in at least one instance, the design includes a number of synergistically prepared features.

In one example, the mass spectrometer of the present invention comprises a single unit that can operate within a simple cylindrical vacuum chamber having a port for inlet gas, several low voltage cables, and a port for a roughing pump. These ports may be implemented with thin conduits or wires fed through the vacuum chamber wall and embedded in epoxy.

An example mass spectrometer can be designed with a number of potential applications in mind, but will likely have common performance requirements. For example, a mass spectrometer (i.e., capable of distinguishing ions at one or more integer mass units apart) may be designed and constructed for unit resolution with sufficient sensitivity to detect species that constitute 0.5% or more of the analyte gas at operating pressures of le-4 pascals (le-6 torr). The mass spectrometer can also carry its own high vacuum pump thereon; although less versatile than designs including high vacuum pumps and low vacuum pumps, substantial savings in cost, weight, and complexity may be valuable. Such an exemplary mass spectrometer may be capable of operating independently for long periods of time with low power consumption and low maintenance.

Instruments that provide this level of performance have limited utility if the cost of production is comparable to that of existing commercial instruments (e.g., tens of thousands of dollars). The mass spectrometer can be quite inexpensive (e.g., on the order of $ 1000), making it suitable for large-scale deployment in new applications. Among the cost considerations of mass spectrometers are ease and complexity of manufacture; difficult or skilled manufacturing techniques and/or a large number of parts can make the design more expensive to build.

Minimizing power consumption is also important for certain applications. For example, mass spectrometers meeting the above specifications may be well suited for a variety of remote or portable applications where the mass spectrometer is capable of consuming batteries, solar energy, wind power, or another energy source for extended periods of time.

In one embodiment, the miniature mass spectrometer is a single focus, 180 degree sector magnetic mass spectrometer. Sector magnetic mass spectrometers can be constructed using multi-layer planar assemblies, which greatly reduces the cost of the instrument, since most simple fabrication techniques are two-dimensional. The geometries involved are simple and do not require high power RF oscillators or high speed timing capabilities, as may be required in the case of a quadrupole mass spectrometer or a time-of-flight mass spectrometer, respectively. Other mass spectrometer types (e.g., ion trap or fourier transform types) can be demanding in terms of geometry, power, or complexity.

A set of permanent magnets and yokes create a magnetic field for the mass analyzer. This is an obvious option, with the ready availability of neodymium iron boron (NdFeB) magnets; for small instruments, the electromagnet requires too much power. Furthermore, a second benefit is that permanent magnets can be utilized. By carefully selecting the size of the pole piece (pole piece) for the yoke, the design enables the ion pump to be incorporated into the same magnetic circuit in which the analyser is housed, thus saving complexity, size and number of components. The sector magnetic analyzer may be 180 ° in length, simplifying layout and minimizing design size by placing the ion source and detector on the same side of the instrument. The design of each subsystem of the mass spectrometer is detailed in the following sections.

In another embodiment, the upper and lower mass analyzers include electric fields in the shape of sectors, changing the overall mass spectrometer topology to that of a Neille-Johnson type double focus mass spectrometer, which may more than double the mass resolution.

3.1 vacuum System design

During operation, the entire length of the ion flight path is maintained under high vacuum, i.e., at a pressure below le-4 pascals (le-6 torr). At higher pressures (lower vacuum), the mean free path of the ions becomes too short to allow them to traverse the entire length of the flight path. This standard alone requires the use of a vacuum system with very tight tolerances to reduce the leak rate, and the use of a vacuum pump capable of producing a high vacuum.

At the same time, the vacuum system of the mass spectrometer may have to cope with the gas that is constantly rushing in; gas entering the system from the inlet should be constantly pumped back or trapped to avoid the vacuum chamber pressure rising to unacceptable levels. Thus, the vacuum system may also include one or more vacuum pumps that are capable of pumping faster than the inlet leak rate.

In most mass spectrometers, the vacuum system is a very expensive part of the design. Vacuum systems may not be a large proportion of the total cost compared to the cost of typical instruments, but for small inexpensive designs, the vacuum assembly alone can easily dominate the budget. High vacuum components, even standard fittings, are very expensive. Almost every component is constructed of machined or formed stainless steel, and each component is often made with welds. Mass spectrometers typically use custom vacuum assemblies due only to the geometry of the instrument. For example, fan magnetic mass spectrometers typically have a formed, thin-walled, stainless steel tube weld welded to a high vacuum flange for a mass analyzer. This is generally due to the fact that the flight path of the mass analyser should be embedded between the poles of the magnet and the gap is an unusual standard dimension.

In addition, an electrical signal is fed into or out of a typical mass spectrometer vacuum system using one feedthrough for each voltage in the system. In conventional mass spectrometers, there may be five to ten or more separate potentials anywhere at different points within the vacuum system. Feedthroughs for high voltages can be particularly expensive because they are made of brazed kovar conductors with ceramic insulators and stainless steel flanges. Due to the cost and complexity of using multiple feedthroughs, including high voltage feedthroughs, it is stated that mass spectrometers can be designed and built to operate using a small number (e.g., one or two) of signals that penetrate a vacuum chamber.

One way to reduce the cost and complexity of vacuum systems is to reduce the number of components involved. For example, a miniature mass spectrometer can be designed to be mounted entirely (including magnets, power and control electronics, high vacuum pumps, and ion optics, etc.) in a vacuum chamber having a diameter of 100mm and a length of 150 mm. The exemplary mass spectrometer can be mounted on a single vacuum flange through which all of the electronic signals and the inlet gas pass, so for simplicity the vacuum chamber can comprise a cylindrical tube of 100mm diameter. In fact, a simple but smaller vacuum chamber can be constructed to reduce size and weight in accordance with the outline of the instrument.

To reduce the number of electrical feedthroughs, the data can be processed digitally and control signals can be generated within the vacuum enclosure by a control system carried. In this way, the system uses one, two, or three low voltage electrical signals (e.g., power and one or two data lines) fed through the vacuum chamber wall. Since high isolation is not required, these electrical wires can be simple length cables embedded in low outgassing epoxy. The ground reference can be the chamber itself.

Alternatively or additionally, the system may be capable of wirelessly transmitting data through the vacuum chamber wall (e.g., via an infrared signal or RF channel), which necessitates a separate electrical feedthrough for power only. Furthermore, the system is capable of being inductively powered (e.g., via a coil loop antenna), which eliminates any need for feedthroughs connecting the interior and exterior of the vacuum chamber.

In another example, the miniature mass spectrometer contains a cooperatively prepared ion pump designed to use the same permanent magnet and yoke assembly as used by the mass analyzer to maintain a high vacuum within the vacuum chamber. The ion pump itself may not be sufficient to evacuate the mass spectrometer from atmospheric pressure and therefore a valved port can be provided to rough pump the chamber to the point where the ion pump can be started. The port can be mounted on the same flange as the electrical feed-through and the inlet.

3.2 Mass Analyzer design

The resolution of a mass spectrometer can be heavily dependent on the design of the mass analyzer. In general, the stronger the magnetic field, the smaller the radius of curvature. In one example, the mass analyzer in the mass spectrometer is a 180 ° magnetic sector with an ion flight centerline radius of 23 mm. This is partly a practical consideration; a 50mm x 25mm NdFeB magnet can be used without custom fabrication and some clearance between the ion flight radius and the magnet edges accommodates any defects in the nominal circular flight of ions caused by the non-linearity of the magnetic field.

Selecting a sector length of 180 deg. makes it possible to improve the spatial separation between ion beams of adjacent masses, since the flight of each ion is more in that sector. Second, with a 180 ° fan, both the ion source and the detector are located on the same side of the mass analyzer, which results in a more compact design and fewer difficulties (if any) associated with the placement of the yokes. Larger instruments typically do not enjoy this benefit because they have separate vacuum compartments for the ion source and detector, and because the fan length in these instruments is typically limited by the size of the magnet.

There is a trade-off between field strength and weight and cost. When a high-grade (N52) ndfeb magnet is used, the maximum magnetic field strength of the permanent magnet used is in the range of 0.5T to 1T. Higher fields require more coercive force, more magnet thickness in the direction parallel to the gap, and more iron in the return path of the magnet. This can result in heavier and larger designs. However, stronger magnetic fields, such as those created with a vanadium permendur yoke or halbach array of neodymium-iron-boron magnets, improve resolution at low masses, while the higher voltages achievable maintain the above light mass resolution.

Also, there is a trade-off between resolution and signal strength and cost. Narrowing the filter slit results in higher resolution, but fewer ions complete the flight, which causes the detector gain and sensitivity to become more important. Furthermore, as the slit becomes narrower, alignment of the slit with the axis of the ion beam becomes more critical, which leads to tighter tolerances and higher costs.

One illustrative design eliminates the need for filter clamping and alignment by cooperatively preparing the slit with the housing of the analyzer. Furthermore, the slits themselves are mounted on a fold integral to the frame of the analyzer, so that the geometry is variable at the fitting; the slit width may be varied to change the operating point on the signal/resolution curve. In some cases, an actuator, such as a lead screw, piezoelectric assembly, or shape memory alloy assembly, actively changes the slit width, for example, in response to calibration, operation, or feedback during calibration and operation.

Fig. 1C shows a Computer Aided Design (CAD) model of the yoke 114 of fig. 1A. It can be made of 1008 mild steel and houses a pair of 50 x 10mm N52 neodymium iron boron magnets 112 in a sector magnetic mass analyser 130. In one embodiment, the cross-section of the yoke 114 increases from the leading edge of each magnet 112 to 25 x 50mm at the trailing edge of each magnet 112. The mass of the yoke including the magnet 112 is approximately 1.4 kg. The yoke 114 also contains features for mounting; a pair of holes in the return path allow the magnet (which is itself the heaviest part of the mass spectrometer) to be bolted to the vacuum flange.

As shown in fig. 1C, the cross-section of the yoke 114 may be substantially constant outside the magnet. A gap of 10mm is left between the trailing face of the magnet 112 and the yoke 114 to avoid shorting the magnet 112. The gap between the pole faces is 10mm, which is approximately the same air gap as the magnet thickness. This configuration produces a magnetic field ranging from approximately 0.6T at the edge of the pole face to approximately 0.8T at the center. This magnetic field inhomogeneity causes ion beam trajectory errors and lower resolution.

Fig. 1D shows an alternative yoke 214 suitable for holding one or more magnets 212 in place around the mass analyzer 130. The yoke 214 guides the magnetic flux generated by the magnet 212 into the two field regions 211a and 211b having different field strengths. The ion pump 120 is positioned within the first field region 211a, which may have an intensity of about 0.1T, and the mass analyzer 130 is positioned within the second field region 211b, which may have an intensity of about 0.7T.

Given the field strength and ion flight radius, it is a simple matter to calculate the range of ion energies and hence the ion acceleration potential required to run a mass spectrometry scan. The first is force balance: in a mass analyser, the force required to keep ions on a circular trajectory is equal to the mass of the ions multiplied by the centripetal acceleration, and due to the charge of the ions and the applied magnetic field, this force is provided by the lorentz force, qvBsin θ ═ mv²/r

Wherein B is the magnetic field strength in Tesla; v is the ion velocity in m/s; θ is the angle between the ion beam plane and the magnetic field in radians; m is the ion mass in kg; q is a member charge in units of C; and r is the radius of curvature of the ion in m.

The velocity gives the voltage range needed to accelerate the ions. The final ion velocity, i.e., the velocity of the ions as they exit the ion source into the analyzer, is proportional to the voltage E across the electrodes in the ion source,

these equations can be combined to give the relationship between ion mass and the potential required to accelerate the ion in order for it to reach the detector,

thus, as expected, there is an inverse relationship between the required electric field and the mass of the ions. Given a constant charge, heavier ions require more kinetic energy to traverse the analyzer at the appropriate radius. Assuming that each molecule is ionized individually (i.e., q is 1.6e-19C) and within the desired mass range (10 to 44AMU (m is 1.66e-26 to 8.3e-26kg)), an analyzer radius r of 23mm and a perpendicular B field (θ is 0), the equation can be simplified to,

for an operating point of B-0.6T and a mass range of 10-44AMU, the voltage E of the accelerated ions should be swept from about 208V to 915V. Given the dielectric strength of a high vacuum, these potentials are attainable. Furthermore, there are many methods that can generate these voltages efficiently. Voltage generation will be discussed in subsequent sections.

Fig. 2 is a graph of ion source potential versus ion mass for different magnetic field strengths. Note that since this is an inverse power function, the resolution will decrease as the ion source potential decreases, since the same variation in ion source potential will span a much larger mass range. This is an essential feature of the fan magnetic mass spectrometer and the design is not different. This problem is discussed in more detail below.

3.3 ion Source design

The ion source affects the efficiency and performance of the mass spectrometer. Ions are typically formed by electron ionization; the electron gun generates an electron beam that interacts with the sample gas to form positive ions. Such ion sources have historically been referred to as electron impact ionization (electron impact ionization); however, due to the fluctuating nature of the electrons, the exact mechanism of ionization is independent of particle collisions.

The ion source may be located far enough from the yoke structure that fringing fields from the magnet do not affect the trajectory of the electrons. In some cases, the distance between the ion source and the magnet yoke is about 30 mm. Furthermore, the ion source is designed to have a vertically oriented electron beam, which is substantially parallel to the fringe field of the magnet. This reduces the chance that the electron beam is sent out of the way by stray fields.

3.4 Electron Source design

The electron beam is typically thermionically generated by heating a hot wire (usually tungsten or an alloy) to an incandescent state in order to add sufficient thermal energy to some of the electrons in the wire so that they can overcome the work function of the host metal and escape into the surrounding vacuum. An electrostatic field is used to remove the escaping electrons from the region surrounding the wire. This process of generating electrons is generally inefficient; in addition, the probability of interaction between electrons in an electron beam causing ion formation and molecules in the sample gas is also low, about 0.1%.

Ideally, for subsequent flight through the analyzer, the ions are emitted from the ion source in a collimated beam having a suitable geometry. In practice, however, the ionized molecules have a random distribution in the ionization region, and only a small fraction of the generated ions are ejected from the ionization region in the appropriate direction for analysis.

To compensate, many conventional mass spectrometers use an electrostatic field generated by electrodes (often called repellers) in the ionization region to push ions towards the analyzer; however, the field generated by this electrode is rather low. As a result, the ion yield of mass spectrometers using thermionic electron guns is very low. Therefore, a high current electron beam is desirable to increase the total yield of ions, but this would require a large power input.

There are at least three techniques that can improve the efficiency of ion sources. By using improved emissive materials for a particular filament power, the electron yield can be increased. By changing the trajectory of the electron beam (e.g., replacing the straight trajectory with a spiral) to increase the probability of interaction between the electron beam and the sample gas, the yield of ions can be increased. Eventually, it may be possible to trap more of the ions that should be formed but that otherwise are not pushed into the analyzer. Highly efficient emissive materials and methods of increasing ion yield were examined.

In one or more embodiments of the mass spectrometer of the present invention, the ion source is designed to improve ion yield. The illustrative ion source operates by ionizing a large number of ions using a large diameter electron beam, producing an ion beam with broad divergence, and then collecting and collimating these ions into a uniform ion beam using a series of electrostatic lenses. A large cylindrical electron beam is generated by a simple low power tungsten filament and a circular hole in the anode. This structure is called a pierce diode and is well understood; it has been extensively studied in the vacuum tube age and is presented in the literature references. The electron beam is very large, 3mm in diameter, and is used to ionize a large amount of sample gas. However, instead of directing these generated ions through an adjacent narrow mechanical filter, the entire volume is collected and focused with an electrostatic lens.

In a pierce diode, the current density of the current emitted from the anode hole is,

wherein, I_maxIs the current density, with the unit of A/m ^ 2; v is the voltage between the anode and cathode in volts; r is the radius of the anode hole, singlyThe bit is m; and d is the distance between the anode and cathode in m. For a distance d of 5mm between the filament and the ion source inlet and a potential V of 70V, the emission current is 120 μ Α. The emission angle of the pierce diode is θ r/3d, where θ is the beam angle in degrees; r is the radius of the anode pore in m; and d is the distance between the anode and cathode in m. In one example, the pierce diode may have a beam angle of 0.1 °. The electron generating emissive material will be able to produce a 120 mua stream of electrons within a 3mm diameter circle, the 3mm diameter circle being the diameter of the aperture in the anode.

The space charge limited emission from an incandescent tungsten filament as a function of temperature is:

wherein i_maxIs the emission current density of the emission surface in units of A/m²(ii) a T is the surface temperature in K. At 2500K, the current density from the tungsten emitter is 3170A/m². In one example, the ion source includes a source having a thickness of 4e-6/m²An emitting surface of area arranged at 7.1e-6/m²The emission surface is capable of generating an electron current of 120 mua. In one case, the emitting surface is formed by a tungsten filament having a length of 3mm and a diameter of 0.4 mm.

Alternatively, a thinner coiled tungsten wire can be used to create the emitting surface area. The thinner coiled filament wire is less thermally conductive, which results in a more efficient system because less heat is carried out from the filament power lead and can operate at higher voltages and lower currents for the same power input. A 12 μm diameter tungsten wire having fifteen turns with a 1mm turn diameter and 0.2mm pitch, has a surface area of 4mm ^2 and a length of 3 mm. Such a coiled filament may be supported by a support structure made of glass or ceramic insulator or copper conductor.

Filaments having substantially this configuration have been mass produced as flash lamp bulbs commonly referred to as PR-2. PR-2 absorbed 0.5A of current at 2.4V and had a coiled filament about 1mm in diameter and about 3mm in length. In one example, the ion source of the mass spectrometer includes a PR-2 flash lamp bulb with a glass bulb carefully removed. The use of vise jaws allows the bulb to be broken without damaging the delicate filament structure in the middle.

The electric field across the pierce diode can be set to 70V. As a result, the electrons emitted from the anode hole of the pierce diode were about 70 eV. This value of kinetic energy is a generally accepted value for maximizing the number of ions generated by electron ionization for a particular electron flow. This is due to the fact that the de broglie wavelength of an electron at 70eV is 14nm, which is roughly the length of the bond between atoms in many molecules. At 70eV, the de broglie wavelength of an electron is given by λ ═ h/mv, where λ is the de broglie wavelength in m; h is the Planck constant; m is the mass of the particles; the unit is kg; and v is the particle velocity in m/s.

3.5 ion lens

Fig. 3 is a diagram of an ion source lens system 300 that focuses ions generated by an electron beam. The ion source lens system 300 includes an entrance 302, the entrance 302 allowing ions to enter an ionization region 308. A repeller electrode 304 charged to a potential whose polarity is opposite to that of the ions repels the ions, and a trap (trap) electrode 306 is opposite the inlet 302. The weak electrostatic field of the repeller electrode pushes ions from the ionization region toward a three-element symmetric electrostatic lens 310 (also known as an Einzel lens), which 310 focuses the ion stream onto a large slit (filter) 312. These ions again diverge across filter 330, however, second two-element lens 320 slightly defocuses the ion beam, changing the focus to a point at infinity from filter 312. In other words, the first lens 310 and the filter 312 spatially filter the ion beam, and the second lens 320 collimates the ion beam to make it more suitable for analysis.

3.6 grid (grid)

The ion source of the present invention includes a control electrode (also referred to as a gate) that shields the anode and cathode of the pierce diode. The potential at the control electrode or control potential can enhance or prevent electron emission from the cathode. The control potential applied to the electrostatic element can be modulated with electronics disposed inside or outside the vacuum chamber and can operate in substantially the same manner as a control grid in a vacuum tube. The signal used to modulate the thermionic emitter can be used with advanced signal processing techniques such as synchronous detection or stochastic system identification to improve the signal-to-noise ratio of the mass spectrometer.

3.7 sample injection

One of the unknowns is how well the electron beam interacts with the incoming sample gas. To increase the interaction between the sample gas and the electron beam, an aperture is provided in the centre of the trap electrode. The sample is then directed downward through the trap, while the electrons are beamed out in the opposite direction.

3.8 Detector design

An exemplary mass spectrometer includes a detector to sense ions in a mass analyzer. The ion beam reaching the detector may correspond to a current on the order of tens to hundreds of femtoamperes (fA). The detector at the outlet of the mass analyzer is able to detect these minute currents and produce a signal above its intrinsic noise floor.

In one embodiment, the detector is a faraday cup followed by a transconductance amplifier with a gain of 50e 9. The faraday cup captures the incident ion beam and recaptures any electrons generated by the secondary emission. Secondary emission is a problem since the incident ion beam can have very large energies (on the order of hundreds of eV). The faraday cup electrode is shaped to capture secondary emissions by providing a deep cavity into which the incident ion beam enters, which again captures all electrons emitted in any direction except vertical exit. However, since the faraday cup is still located in the fringe field generated by the permanent magnet, the cup can capture the secondary emitted electrons.

The transconductance amplifier can be built on a National Semiconductor (National Semiconductor) LMP7721 low input bias operational amplifier (op-amp) or any other suitable op-amp basis. With a power supply operation of 2.5V, the input bias current of LMP7721 is about 3 fA. A 50G omega resistor in parallel with a 5pF silver mica capacitor for stabilization provides the feedback path of the amplifier. The output of this transconductance amplifier drives the front end of an analog-to-digital converter (e.g., ADS 127824 bit analog-to-digital converter by texas instruments). By placing these components close together and under appropriate shielding, the noise floor can be reduced.

Alternatively, the mass spectrometer may include an electron multiplier type detector 400 as shown in fig. 4, the electron multiplier type detector 400 operating in a manner similar to that of a photomultiplier tube without a photocathode. Ions hitting the first dynode 402a eject electrons which fall through a series of dynodes 402b to 402n of progressively higher voltage, producing two or more times the number of electrons per iteration. This electron cloud is then captured and measured by transconductance amplifier 404, but the signal can be many orders of magnitude larger than a simple faraday cup detector without a significantly higher noise floor, thus allowing for a much more sensitive detection. For example, a properly placed four-or five-stage discrete-dynode electron multiplier can give a signal-to-noise ratio improvement slightly above 16-32, while a low number of dynodes reduces dark current.

3.9 high vacuum pump design

The miniature mass spectrometer uses a pump, such as an ion pump or a turbomolecular pump, to maintain a high vacuum of the vacuum enclosure. The ion pump is quiet, clean, and uses no moving parts. In ion pumps, both pumping mechanisms, trapping and adsorption, are operating. Upon pumping, the gas is ionized by high field ionization in a cylindrical anode and accelerated into a titanium cathode or sometimes into a tantalum cathode. Upon impact, the ions are either buried or cause titanium to sputter back into the anode. This constantly renewed titanium layer is a chemical reaction and traps gases by adsorption.

The electrodes for the ion pump are located within a magnetic field, which generally adds mass to the system and complexity to the vacuum chamber. However, the miniature mass spectrometer has been designed with the magnetic circuit located within a vacuum chamber. In at least one embodiment, the dimensions of the pole faces of the magnets are large enough to encompass the footprint of the mass analyzer and ion pump to increase pumping capacity without significantly increasing complexity.

In one case, the ion pump is a diode pump that includes a set of stainless steel hollow cylinders suspended between a pair of titanium plates, the set of stainless steel hollow cylinders being open at each end. The pump is designed to produce the maximum pumping speed in the usable area. Specific geometries and tradeoffs are discussed below.

The ion pump keeps the system pressure low enough so that the mean free path of the ions is greater than the entire flight length of the mass spectrometer. For this miniature mass spectrometer, the length of the flight path is approximately 200 mm. The mean free path of an ion is given by l ═ 3.71e-7/p, where l is the mean free path length in m; p is pressure in units of pascals (Pa).

Generally, the vacuum should be high enough (i.e., the pressure should be low enough) to keep the mean free path of each ion about an order of magnitude greater than the flight length of the mass spectrometer. For a mean free path of 2m, the minimum system pressure is 3.3e-3Pa (2.48e-5 Torr).

3.10 entrance

As shown in fig. 1A, mass spectrometer 100 includes an inlet 180 to allow entry of a sample to be analyzed. The inlet 180 may be of any suitable type. For example, as shown in fig. 5, it may include an inlet 400, the inlet 400 being formed from a semi-permeable hydrophobic plastic film 502 supported by a perforated stainless steel plate 504. The membrane 502 allows sample particles P to diffuse into the vacuum chamber (not shown) at a rate proportional to their exposed surface area, while preventing moisture and liquid ingress. The inlet velocity can be selected so that the pumping system of the mass spectrometer can handle the inlet load at the appropriate vacuum chamber pressure.

4.0 simulation

An exemplary compact mass spectrometer ion optics design was fully simulated using SIMION 8.0, which is a commercial version of the ion optics modeling software package 8.0. These simulations can be used to model ion flight and to set or change device parameters including instrument geometry, magnetic field strength, ion radius, etc.

4.1 size design

Simulations can be used to traverse all design choices (e.g., by simulating choices that affect electrode voltages to properly focus the ion beam). In one example of a simulation, the total height of the analyzer of the mass spectrometer was first set. The vertical dimension is somewhat optional. The height of the permanent magnets used is 10mm and the gap is chosen to match this number. Approximately 1.5mm is left for the thickness of each of the top and bottom caps of the mass analyzer, and the vertical dimension is set to 7 mm.

Fig. 6A is a diagram of the ion source 104 (fig. 1A) and ion source optics 300 (fig. 3) taken from a SIMION simulation of a mass spectrometer. The radius of the mass analyser was set to 23mm (above). Using this dimension as a control dimension, the mass spectrometer ion optics 300 and the remainder of the flight path are designed to be no more than 50mm in length. The electron beam is placed as far as possible from the fan-shaped magnetic mass analyzer 130 (fig. 1A) to reduce the effect of stray magnetic fields on the operation of the electron beam.

The next decision relates to the size of the first lens 310. The first lens 310 collimates and focuses those ions created by the electron beam onto the mechanical filter. This lens 310 is a three-element symmetric lens, also otherwise referred to as a singlet lens, and is described as symmetric in that the first lens element and the third lens element are at the same electrical potential. Such a lens is chosen because it is a variable focus lens that does not change the energy of ions emitted from the other side. Typically, the electrostatic lens is constructed to have a width approximately the same as the length of the elements, with the element pitch being equal to one tenth of the length. Such lenses typically have focal lengths with equal distances on both sides of the lens; thus, the filter 312 immediately following the first lens 310 is the same distance from the lens 310 as the ionization region.

The second lens 320, which is used to slightly defocus the ion beam (e.g., to place its focal point at infinity), is a two-element lens that approximately equally subdivides the region between the first and second mechanical filters. Longer electrode faces provide a slightly more uniform field; the exact placement of the electrodes is somewhat less important.

A second mechanical filter 322 after the second lens 320 further limits the ion beam spread to reduce stray ions reaching the detector. Since the fringing field of the magnet is very strong and may push the ion beam out of the way before it reaches the filter 322, the filter 322 is placed 10mm from the nominal entrance of the fan-shaped magnetic mass analyzer 130 (fig. 1A, not shown).

Note that all of the electrodes are not simply flat surfaces along the ion flight path, but rather all extend perpendicularly away from the flight path. Although the plate will behave identically in this simulation, it is practically almost impossible to prepare. The depth of the electrodes allows them to be mounted on a common plane; simulation in this way requires that the electrodes be mounted in some way as a reminder. The shape of the back side of the electrode is not important.

4.2 ion flight simulation

The entire mass spectrometer design was simulated and built to meet the preliminary design work. Simulations were performed for ions of masses 10AMU to 44 AMU. The voltage required at each electrode is approximately as predicted.

Fig. 6B is a simulation showing the flight of carbon dioxide molecules from the ion source 104 through the ion source optics 300 and the mass analyzer 130. SIMION does not mimic space charge, ion collisions, or secondary electron emission; simulations were performed for individual isolated ions in the provided geometry. The influence of the fringe electric field was simulated.

Note that it is important that the simulation is performed under ideal conditions, and improper selection of initial conditions will easily lead to off-tracking. For example, simulations of stationary ions starting at the dead center in the ion beam may perform much more satisfactorily than ions near the edges of the ionization region with initial velocities perpendicular to the desired path. Improper selection of initial conditions may lead to the belief that a design will operate at much higher ion efficiencies and resolutions than the design can actually produce. Therefore, the initial conditions of the ions in the flight path should be carefully selected.

The initial energy of the ions is selected to have a gaussian diffusion centered on the thermal energy of the gas molecules at room temperature. The average translational energy of the gas molecules of an ideal gas is E ═ 3kT/2, where E is the kinetic energy, in units of J; k is the Boltzmann constant (8.617e-5 eV/K); and T is temperature in K. At room temperature, E is approximately equal to 0.015 eV. Therefore, subsequent trajectory simulations were performed using a Gaussian distribution with an initial kinetic energy of 0.015eV average and 0.005eV standard deviation.

The initial direction of the ions is set using a uniform distribution radially across 360 degrees. The initial position of the ions is set using a uniform distribution of cylinders spread over the projection of the aperture through which the electron beam enters the ionization region.

Fig. 6C is a detailed view of the ion source 104 and the first lens 310 of the mass spectrometer 100 (fig. 1A). Ions originate at the center of ionization region 308, generated by a vertical cylindrical electron beam directed vertically out of the page. An initial trajectory of ions with random directions and random kinetic energies is generated. The repeller electrode 304 directs ions toward the first lens 310, and the first lens 310 focuses the ions onto a slit 312 (not shown in fig. 3, 6A, and 6B). The black trace in the simulated plot is the ion trajectory calculated given a real set of initial conditions. Due to the low ionic current magnitude, it is reasonable to ignore space charge.

Figure 7 is an isometric view of mass spectrometer 100 with a physical layout in two dimensions and potential energy in the third, vertical dimension. The potential energy is highest in the ion source 104, then drops off at the first filter 312, increases again in the second lens 320, and then drops off in the mass analyzer 130. Here, the advantages of a longer, lower voltage second lens 320 become more apparent; any slight misalignment in the higher voltage lens may cause much larger trajectory errors in the ion beam because the potential 'barrier' over which the ion beam flips becomes much steeper.

4.3 Electron Source simulation

Fig. 8 and 9 show simulations of an electron source assembly 800 or a pierce diode, the electron source assembly 800 or pierce diode including an electron source 102, the electron source 102 being a filament or any other suitable type of electron source. The electron source 102 is arranged with an area bounded on three sides by the cathode 810 and on the fourth side by the anode 830, and the electron source 102 is here simulated as a cylindrical electron source with a diameter of 1mm and a length of 3 mm. The control electrode 820 is positioned between the source 104 and the anode 830. The control electrode 820 and the slit or aperture in the anode 830 allow electrons to propagate to the ionization region in the ion source 104 (fig. 1A, 3, and 6A).

In operation, cathode 810 is maintained at a potential of about 70V below the potential of anode 830, and anode 830 can be at a potential of about 100V to about 5 kV. Control electronics (not shown), which may be disposed within the vacuum chamber, changes the potential of the control electrode from about 140V below the anode potential to about 0V below the anode potential. When the control electrode is off (i.e., at a potential equal to the anode potential), the cathode 810 and anode 830 operate to push electrons out of the assembly, as shown in fig. 8. FIG. 8 illustrates the focusing effect of the anode; the emitted electron beam is collimated to have a narrow beam angle. The electron beam narrows slightly as the source potential ramps from 150V to 900V. Applying a voltage to the control electrode 820 reduces the intensity of the electron beam. For example, the control electrode 820 is held at a potential of 100V below the anode potential, as shown in FIG. 9.

5.0 Structure

5.1 base plate

Mass spectrometers use a plurality of electrostatic elements that remain aligned while still being electrically isolated. To reduce the number of components, a separate, inexpensive substrate is selected to maintain all electrode alignment and isolation.

FR-4 printed circuit board material was selected as the substrate on which the mass spectrometer was built. The reasons for this choice are manifold. FR-4 glass fiber Printed Circuit Boards (PCBs) are inexpensive in large numbers due to the large number of facilities dedicated to producing custom boards and the highly automated processes involved. PCBs can be fabricated with very small feature sizes and extremely high precision; typical PCB companies such as Sunstone (www.sunstone.com) are capable of producing feature sizes as low as about 0.15mm in prototype quantities and smaller features with one tenth of the positioning accuracy in large production quantities. PCBs, nominally designed for electrical components, have very high dielectric strengths of about 1e7V/m to 2e7V/m, which are sufficient for the voltages involved in this mass spectrometer design. Finally, the PCB is mechanically very strong, consisting mainly of woven glass fibre mats and epoxy, and is a good choice for keeping the electrodes separated.

Since the PCB is designed for implementation of the circuit, the electrodes of the mass spectrometer and the circuitry driving the mass spectrometer may be contained on the same substrate. An additional benefit of using PCD material as the substrate is that there are many variations in the composition of printed circuit boards, including ceramic printed circuit boards, and the underlying material can be changed relatively easily if potential defects in FR-4 prevent the design from working properly.

However, PCBs do have several potential drawbacks. The FR-4 printed circuit board is made of copper on a glass reinforced epoxy board. Thus, the substrate material has the potential to absorb and adsorb water and gas (diffuse into the host material and attach to the surface, respectively). These absorbed and adsorbed molecules can then be slowly released into the vacuum system of the mass spectrometer, which prevents the system pressure from dropping low enough that this background concentration of gas remains visible above the spectrum of the incoming gas. These potential problems are not without solution. There are two main countermeasures to these problems; driving the absorbed and adsorbed gases out of the material or encapsulating the material within a low outgassing conformal coating.

It is well known that increasing the temperature of a material tends to assist in the removal of absorbed and adsorbed gases in a vacuum. The standard procedure when constructing a vacuum tube is to degas the tube while it is still on the exhaust vacuum manifold by means of a heating element. Degassing is typically accomplished by: heating the electrodes of the tube by radiation by operating the filament of the tube; or by absorbing an electron current that heats the anode and other electron collecting electrodes of the tube; or by frying the tube. "blasting" involves heating the electrodes by joule heating using eddy currents induced in the electrodes by an RF coil held outside the housing of the tube.

Encapsulating venting materials also has precedent. Outgassing of materials is often a problem on spacecraft, particularly satellites, where gases may be emitted from one surface and re-adsorbed by other critical surfaces such as sensors. Thus, conformal coatings are often tested for outgassing performance. There is a standard test method for determining venting performance, ASTM E595-07. One well-known low outgassing conformal coating is parylene, and parylene coating is a service provided by many process plants.

Embodiments of the mass spectrometer of the present invention may include a distributed network of resistive heaters added to the bottom of the PCB substrate. These heaters enable heat to be added to all points on the PCB at the same time. In another embodiment, these resistive heaters are replaced or augmented by a simple network with thin traces that is similar to the resistive array on most automotive rear windows.

5.2PCB design and Structure

Fig. 10 shows a CAD layout of a printed circuit board where all the sheets are connected (cut apart after build-up to reduce cost). To reduce the overall size of the mass spectrometer, several layers of PCBs are used. The bottom layer of the printed circuit board carries the electronic package, which is described in detail in the next chapter, while the upper two layers of PCB form the bottom and top covers of the mass analyzer.

Fig. 11 illustrates a CAD model of an example quality analyzer component 1100. The substrate 190 is sandwiched between a top cover 1102 and a bottom cover 1104 with the analyzer electrode 1110 in between. The substrate 190 is attached (e.g., by a 20mm long M3 hex clinch nut) to the circuit board 1120 by a clinch nut (standoff). The screws pass through mounting holes in the analyzer ring, the lower layer PCB of the mass analyzer, and the hex clinch nuts. A shear pattern (cutout) in the upper PCB of the mass analyser allows the screw head to be mounted undisturbed. This allows the top cover of the mass analyser to be removed for electrode alignment without requiring removal of the mounting hardware.

An electrical feedthrough connects the mass analyzer board to the electronics board. The low voltage digital and analog power pins are carried on two rows of 20mm high, 2.54mm spaced pin heads. The high voltages used for electrostatic lenses are more difficult; there is no 2kV rated electrical mezzanine connector. Instead, a suitably spaced row of holes in the mass analyzer board and electronics board are fitted with 25mm M2 hardware after the two boards are mechanically mounted together. A copper ring around each hole acts as an electrical contact.

5.3 electrodes

Using the PCB as a substrate, the electrodes can be prepared and assembled onto the PCB. The geometry for these electrodes and the relative spacing of these electrodes can be obtained directly from the simulations described above. The electrodes have symmetry through a vertical axis (an axis out of the plane of the ion flight path). When manufacturing in two dimensions, most of the simple manufacturing techniques are greatly simplified; the clamping or complex machinery required to install an assembly that performs operations on more than two shafts increases the cost of the finished part.

The electrodes were cut from type 303 stainless steel. This stainless steel has a number of beneficial properties; the host metal and its surface oxides are electrically conductive, chemically non-reactive and have a low affinity for gas adsorption. It is a common material used for high vacuum work; most high vacuum components are constructed of 303 stainless steel or similar materials.

Type 303 stainless steel is one of the easiest to machine. However, some of the features required to produce these electrodes are very small, on the order of hundreds of microns, and these kinds of features are not conducive to preparation by cutting tools. Typically, the cutting tool imparts too much force to make the thin-walled feature. Thus, the fabrication technique chosen for the preparation of the mass spectrometer electrodes is wire electro-discharge machining (wire EDM). Alternatively, a symmetrical assembly of the mass spectrometer (possibly with material variations) can be built as a stamp (extrusion). The stamp can then simply be cut into parts, which results in a very economical construction method.

The electrodes at different potentials are separate components, but efforts are made to simplify the manufacture of mass spectrometers by allowing all of the electrodes at the same potential to be cut together from the same raw material. In addition, all features necessary to install these components are designed into the tool path. So that each electrode can be cut in a single pass.

5.4 Mass Analyzer

Fig. 12 is a CAD model of a mass analyzer electrode. Since the mass analyser is at ground potential, its structural loop is its own structural rigidity and that of the mass spectrometer and encloses all other planar electrodes within the system for electrical shielding. The field generated by the electrodes in the mass analyser should be shielded from the outside world, thus theoretically preventing some stray fields that might otherwise interfere with the electronics.

The mass analyser also has a pair of fine features at the entrance and exit of the magnetic sector. These features are mechanical filters that limit the width of the detected ion beam, which maximizes the likelihood that the detected ions will have the desired mass. The filter is a slit that is tens to hundreds of μm wide and, as seen from the simulation, has a direct impact on the sensitivity and resolution of the mass spectrometer. Typically, the slits are manufactured and installed separately in most mass spectrometers; here, they are prepared in conjunction with a mass analyzer, which both ensures their collinearity with the ion optics and minimizes cost by minimizing the number of parts and eliminating any need for slit alignment.

Fig. 13 illustrates a thin-walled adjustable flexure 1300 formed from the same piece of material (e.g., PCB material) as the base plate 190 (fig. 1A) using wire EDM. The flexure 1300 includes an L-shaped member 1304 connected to the base plate 190 via a hinge portion (hinge) 1302. Pushing the upright of the L-shaped member 1304 with an actuator, such as a lead screw (lead screw)1310, causes the L-shaped member 1304 to rotate about the axis of the hinge 1302, which in turn reduces the width of the slot 1308 in the ion (or electron) path. The stop 1306 prevents the L-shaped member 1304 from closing the slot 1308 too much. Unscrewing lead screw 1310 causes hinge 1302 to return to a relaxed position, at which point L-shaped member 1304 no longer closes slit 1308. This flexure can be placed before or during operation to give great control over the resolution and sensitivity of the instrument.

In another embodiment, the flexure is actuated, for example by a lead screw equipped with a motor or by a piezoelectric actuator. This allows the mass spectrometer to automatically optimize its sensitivity to ongoing resolution, expanding the slit to increase ion current for weak signals and narrowing the slit for better resolution when analyzing ions of adjacent mass.

5.6 Electrostatic lens electrode

Smaller electrodes used in ion sources, mass analyzers, and detectors can also be cut out of the same raw material as the mass analyzer using wire EDM. In addition to the actual faces, at least two mounting features can be cut into each electrode, which corresponds to features in the mass analyzer PCB, thus minimizing the chance of angular misalignment.

5.7 Electron Beam electrodes

The electron beam in the ion source of the mass spectrometer also requires electrodes that are normally working and which are out of the plane of the ion source electrodes. Since the electron beam runs perpendicular to the ion beam from bottom to top, different preparation techniques can be used to prepare the ion source electrode. For example, the electron beam electrodes, traps (traps), and electron focus rings can be printed on a small PCB and mounted to the main PCB with M2 hardware.

The electron focus ring also serves as a physical seat for the PR-2 flash lamp bulb providing the tungsten filament; the focus ring allows the filament and its support to penetrate the electronic PCB while keeping the mounting flange of the bulb restricted. An M2 screw 25mm in length passes through the focus ring PCB, through the flashlight bulb base, and through the electronics PCB. The M2 screw is held under tension, which holds the flashlamp bulb in place while allowing alignment; the bulb base can be moved slightly before the mounting screws are tightened.

The trap electrodes were mounted on the upper mass analyser PCB, spaced apart by a distance of 200 μ M by an M2 spacer and screwed through to the mass analyser. A long M2 screw consisting of a 30mm long threaded rod of M2 and a safety nut (jam nut) electrically connects the well electrode to the electronics board that generates the well potential.

5.8 electrode finish

The electrodes of the miniature mass spectrometer are assembled to the printed circuit board substrate as standard electrical components. For example, they can be mounted by cutting a notch in each electrode and brazing a small stainless steel pin to the electrode body using a hydrogen torch (hydrogen flame torch) and silver solder. This approach allows the electrodes to be mounted without protrusions on top of the electrodes so that there is no problem of aligning the mounting features of each electrode with the upper PCB cover of the mass analyser. Alternatively, the upper PCB cover may include a shear pattern to provide clearance for mounting screw heads. The finished version of the mass spectrometer used a combination of M2 and M1.6 hardware to attach each electrode to the PCB.

Figure 14 shows two steps in the process of assembling the mass spectrometer electrodes. When the electrodes are removed from wire EDM (left side of fig. 14), the cut face of each electrode is covered with a thick oxide layer. The electrode was immersed in a 30% nitric acid solution for 30 minutes followed by two changes of absolute ethanol in an ultrasonic wash tank at 50 degrees celsius for 30 minutes (right side of fig. 14). This process removes the oxide layer, leaving the underlying bright metal.

5.9 magnet

In one example, the mass analyzer includes a pair of NdFeB magnets held in alignment by a soft ferromagnetic yoke as described above. A mounting surface is provided on one edge of the yoke, drilled and tapped for M3 hardware. This mounting face is attachable to an electronic device PCB.

5.10 ion Pump

A cooperatively prepared ion pump can be installed in a volume small enough to contain only the unused half of the magnet face. Since the ion pump operates at high voltage, the printed circuit board serves to isolate the magnetic pole face from the ion pump electrodes. The entire ion pump can then be mounted in a volume of 50 x 25 x 7 mm.

Fig. 15 is a CAD model of the ion pump anode 120. Typically, ion pumps are designed with bundles of stainless steel tubes that are bundled together to form the anode. Such a process is expensive and labor intensive; the anode of the compact ion pump on this mass spectrometer consists of a series of cells cut out of a stainless steel plate in one pass using wire EDM.

The pumping speed is proportional to the diameter and number of cells; increasing these values to a point increases the speed of the ion pump. Given the limited space available and the higher field strength than standard B field strength, more cells are added instead of increasing the diameter of the cells. Another criterion indicates that the length of each cell should be about 1.5 times greater than the diameter of the cell; if a 3.5mm plate is used, it is difficult to do so without designing a fairly small unit.

The cathode of the ion pump comprises a pair of 0.5mm thick titanium plate cathodes with mounting tabs arranged such that they are interleaved with the four mounting tabs of the anode. The mounting holes in the ion pump electrodes mate with holes in the PCB substrate.

5.11 Assembly

Fig. 16 is a photograph of a complete mass spectrometer with the top cover and yoke removed. As designed, the mass spectrometer can be assembled without the use of any complex tools or techniques. All mounting hardware can be attached using a single 1.5mm in-line screwdriver and long-nosed pliers. The alignment feature on the printed circuit board in the form of the profile of each electrode facilitates assembly and enables the insertion of a clamp (jig) into the ion flight path, enabling the electrodes to be pressed against the ion flight path before the screw is fully tightened, which ensures that the electrode faces remain parallel. Since all electrodes are designed with a 0.5mm gap between adjacent features, the other electrodes can be spaced apart with 0.5mm spacer blocks.

Fig. 17 shows a photograph of a filament irradiated from the side with a flash lamp (left) and a photograph of an entrance slit of a mass analyzer (right). The filament alignment can be done optically; a bright flash lamp can be illuminated from the side of the partially assembled mass spectrometer towards the filament and the electron focus ring electrode moved into the plane until the center of the filament is clearly visible from above. This is a relatively simple process due to the large volume of the ion source and the large diameter of the electron beam, since visibility through the path of the electron beam is good. The slits in the pleats forming the mechanical filter can be adjusted by tightening or loosening the lead screw. A macro photograph of the analyzer entrance slit illuminated with a magnesium light (Mag-Lite) flash lamp from above is shown in the right photograph of fig. 17.

Once the electrodes are assembled, the top cover of the mass analyser can be mounted and secured through with a separate M2 screw. The trap electrode is then mounted over the analyzer lid and also screwed through. Then, the PCB assembly is bolted to the yoke; alignment marks (alignment marks) indicating the relative positions of the poles are etched into the printed circuit board copper layer outside the analyzer PCB assembly. A slightly oversized mounting hole allows the magnet to be slightly adjusted to match those alignment patterns on the outside, thereby ensuring alignment with the presently capped mass analyser.

Figure 18A is a photograph of an assembled mass spectrometer attached to a 6 "confrat flange. The final assembly of the mass spectrometer contains a vacuum chamber which can be as simple as a steel cylinder or a glass cylinder. The yoke of the mass spectrometer is bolted through a hole in a confrat flange that is tapped. A stainless steel hypodermic tube of 1.29mm outer diameter for the inlet and some low voltage leads were fed through the hole in the flange and glued in place with epoxy. The inserted photograph is the side of the vacuum flange opposite the mass spectrometer showing the electrical and gas connections to the instrument. (A port for a roughing pump can be used on this flange; however in this case the roughing port is provided at the other end of the vacuum chamber).

Figure 18B is a photograph of a mass spectrometer mounted on a flange and inserted into the end of a 6 "confrat flanged tee. The distal face of the tee is fitted with an ion gauge (dunivery-stokes company, www.duniway.com) which is connected to an ion gauge controller (Varian model 843, www.varianinc.com/vacuum). The third face of the tee is used for a low vacuum system.

Since the initial gas load from this mass spectrometer is expected to be quite high, a powerful low vacuum system is used. A0.2 m ^3/s turbo-molecular pump (Wai-an V-200) was connected to the Compeltt tee and the exhaust of the turbo-pump was connected to a mechanical roughing Vacuum pump (WeilQi Vacuum 1402(Welch Vacuum 1402)) and cooling was provided by a temperature controlled recirculator (scientific product of VWR) with distilled water as the working liquid.

6.0 electronic devices

In addition to the detector, the electronics that control the miniature mass spectrometer are located on a printed circuit board below the mass analyzer board. For the mass analyzer, the electronic device board was prepared without a solder mask to facilitate outgassing. Physically, the electronics board is placed so that a 20mm M3 clinch nut can be used to mate the electronics board with the hole in the analyzer board, and electrical feedthroughs connect the electronics board to the electrostatic elements and detectors on the mass analyzer board. The electronics board includes two main parts: a power supply section (conversion circuit) and a digital controller. A plurality of independent isolated power supplies operate all sub-sections on the electronics board.

6.1 Power supply (switching circuit)

The mass spectrometer can operate on a single input power supply of up to 1.1A of +12VDC, but the typical supply current when operating under normal conditions is 0.5A. The multiple different supplies are generated internally via one or more dc/dc converters (conversion circuit 150 in fig. 1A). As detailed in the following section, the supply of +12V also serves as the main supply for the lens driver. This supplied "ground" serves as the "ground" for the system and is also connected to the vacuum envelope.

In one example, the switching circuitry generates voltages for the various mass spectrometer electrodes and components including, but not limited to: a microprocessor, a digital-to-analog converter (DAC) and an analog-to-digital converter (ADC) for controlling the mass spectrometer; an analog stage of detector 140 (FIG. 1A); electron sources and electrodes for the electron sources (e.g., filament 102, cathode 810, control electrode 820, and anode 830 in fig. 8 and 9); ion pump 120 (fig. 1A); ion optics 300 (fig. 3); and electrodes of the ion source 104, such as the repeller 304 (fig. 3 and 6A). Suitable voltages include digital logic voltages (e.g., +3.3V, +5V) and potentials of about 100V to about 5kV for the ion pump 120, the electron source, the ion optics 300, and the ion source 104. The mass spectrometer may also include a filter and a regulator to compensate for or correct for fluctuations in the input voltage from the external power supply.

The mass spectrometer may also include one switching circuit 150 for each component and electrode or multiple switching circuits 150 that generate voltages for multiple sets of components and electrodes. For example, it may comprise an isolated +3.3V/1W dc/dc converter supplying digital logic. Digital logic includes a microprocessor and analog input/output (I/O) modules such as DACs and ADCs for controlling the mass spectrometer. The digital side of the ADC of the detector also operates from the digital logic supply. The ground side of the logic supply is connected to system ground at a single point.

The mass spectrometer may also include an isolated + -5V/1W dc/dc converter followed by a pair of linear regulators that provide a + -2.5 VDC supply for the analog stage of the detector. The supply is heavily filtered and lightly loaded, which provides the supply current for the analog half of a pair of op-amp and detector ADCs. This supplied "ground" is connected to the system "ground" just at the detector electrodes to reduce noise.

The mass spectrometer may also include an isolated +3.3VDC/3W dc/dc converter that provides a supply voltage to the filament, which nominally absorbs 2.4V/500 mA. The "ground" of this supply is connected to the filament bias supply, which in turn is 70V below the ion source supply.

The mass spectrometer may also include an isolated +3.3VDC supply, whose "ground" is biased to the trap potential, which supplies the supply voltage for the ADC that measures the trap current of the mass spectrometer. The mass spectrometer may also include an isolated +5.0VDC supply, whose "ground" is biased to the ion source potential, which provides a supply voltage for an operational amplifier that drives the repeller electrode 304 (fig. 3). The mass spectrometer may also include an isolated 3kV/3W dc/dc converter that provides an anode voltage to the on-board ion pump 120.

6.2 ion optics driver

Five high voltage ratio dc/dc converters (switching circuits) provide electrostatic element potentials. A proportional dc/dc converter generates an output voltage that is linearly proportional to the input voltage of the converter and is useful when a range of output voltages is desired. The input voltages of the dc/dc converters are supplied by an operational amplifier configured such that a portion of the output voltage of each dc/dc converter is fed back to each operational amplifier, which stabilizes the output. The reference of each operational amplifier is provided by a DAC from a digital controller or from a potentiometer for a potential that can be calibrated at one time and that can remain unchanged during operation.

These dc/dc converters (switching circuits) supply potentials for the ion source, electrostatic lenses of the ion source, traps, and biases for the filament. The outputs of all these converters are systematically "ground" by a reference value. While it may be easier to tie these outputs together appropriately (e.g., referencing the trap supply to the ion source supply, rather than to "ground"), the output isolation rating of each of these dc/dc converters is insufficient to do so.

6.3 electrometer

The electrometer connected to the faraday cup electrode is a sensitive transconductance amplifier connected to an analog-to-digital converter, such as the "national semiconductor" LMP7721 operational amplifier in a transconductance configuration with a gain of 5e 10. Parallel to the feedback path is a 5pF silver mica capacitor; the capacitor reduces the gain of the amplifier at high frequencies, thereby reducing high frequency noise present at the amplifier output.

Due to the high gain of the electrometer, leakage currents can cause drift in the electrometer output. To help reduce this drift, a guard ring surrounds the connection connecting the input pin of the potentiometer, one end of the feedback resistor and capacitor, and the electrodes of the faraday cup. The guard ring is driven by a second operational amplifier in unity gain voltage mode (such as LMP7715 of "national semiconductor"), the input of which is derived from the in-phase and nominally grounded input of the electrometer (and slightly offset due to the bias current). The output of the transconductance amplifier is directly digitized by an ADC (e.g., ADS 128124 bit ADC of texas instruments).

The entire electrometer circuit was mounted on an analyzer PCB within a pocket (pocket) cut into mass analyzer electrodes. Together with the copper on the two PCBs, the electrode acts to enclose the electrometer within a faraday cage. The proximity of the electrometer to the faraday cup detector electrode reduces the chance of noise interfering with the signal.

6.4 degassing Heater

The printed circuit board in the vacuum chamber is expected to carry a considerable gas load. A network of distributed resistors is then added to the printed circuit board to ensure that the board temperature can rise high enough to help remove the gases absorbed and adsorbed by the PCB. A plurality of 1W resistors operated by the main +12VDC supply are strategically located and gated by P-channel FETs as on/off or PWM heating control.

6.5 digital controller

Figure 19 is a block diagram of a digital controller 1900 of a mass spectrometer, the digital controller 1900 being built near a processor 1902 (e.g., a 32-bit ARM Cortex-M3 microprocessor (STM32F103CBT6) manufactured by ST microelectronics). The processor 1902 is powered by a power supply (switching circuitry) 150 and is coupled to a Radio Frequency (RF) communication module 1920, the RF communication module 1920 acting as a wireless communication interface for relaying data and instructions between the interior and exterior of the vacuum chamber. The controller 1900 also includes DACs 1904a-1904c (collectively referred to as DACs 1904), ADCs 1906a-1906c (collectively referred to as ADCs 1906), and Field Effect Transistors (FETs) 1908a-1908c (collectively referred to as FETs 1908) coupled to the processor 1902 via a common Serial Peripheral Interface (SPI) bus 1910 on the microcontroller 1900. The entire controller 1900 may be contained within a vacuum chamber defined by the vacuum chamber of the mass spectrometer. For example, the controller 1900 may be mounted or coupled to the electronics board 1120 shown in fig. 11.

In one exemplary controller 1900, there are three DACs 1904a-1904c (e.g., AD5662 DACs), and these three DACs 1904a-1904c are used to set the ion source supply and the potentials on the two electrostatic lenses. There are two ADCs 1906a and 1906b (e.g., AD7680ADC), which two ADCs 1906a and 1906b are used to measure the filament drive current as well as the sink current. Both ADCs 1906a and 1906b operate on a supply biased at a high voltage; the SPI bus for these devices is isolated from the logic level bus by an opto-isolator, such as the ACSL-6410 bidirectional (3/1 channel) opto-isolator of Avago (Avago) technology. Another ADC1906 c is coupled to the electrometer.

DAC 1904 and ADC1906 are connected to SPI bus 1910 of the microprocessor. Each DAC 1904 and ADC1906 has its own dedicated microprocessor GPIO pin for addressing. In addition, several GPIO lines are introduced into the electrometer ADC for other functions (e.g., data preparation, reset). A port extender/LED driver 1912 (e.g., MAX 6696 port extender/LED driver by american Integrated Products) is also connected to the SPI bus 1910 for user feedback and to the three RGB LEDs 1914.

The pin connected to the hardware timer on the microprocessor 1902 serves as the gate drive for the P-channel FET1908a connected to the filament. The filament is driven in a pulse width modulated manner to achieve maximum efficiency. The switching frequency is 100kHz, but can be changed if disturbances are detected during operation.

Other pins on the processor are used to control other peripherals. The degas heater and several power supplies including most of the high voltage supply and the filament are gated by large P-channel FETs (e.g., FETs 1908b and 1908 c). FET1908 is driven by the microprocessor pin so that the filament and high voltage supply can be turned off to save power when the mass spectrometer is not in use.

A pair of pins is used to control and monitor the ion pump. One pin enables the ion pump so that the controller can operate at atmospheric pressure without ion pump arcing. The other pin is used as an analog input to an on-board 12-bit ADC of the microprocessor to monitor the terminal voltage supplied by the ion pump.

Two pins connected to a hardware USART transceiver in the microprocessor are the means of mass spectrometer communication with the outside world. These pins pass through the wall of the vacuum chamber (but may optically transfer data if the vacuum enclosure is made of glass).

In this example, three Serial Wire Programming (SWP) pins specific to Cortex-M3 also pass through the vacuum enclosure, so that the microprocessor's code can be reconfigured without the need to vent the vacuum chamber.

6.6 control software

In one example, control software for a mass spectrometer is written in the computer C language and compiled for the mass spectrometer using an IAR system embedded Workbench (IAR system embedded Workbench) IDE and a compiler for the Cortex-M3 core. The main run loop is a finite state machine that controls the basic operations required to generate a mass spectrum. During each cycle period, the mass spectrometer reads all available data representing the state of the external variable and then runs code that depends on the state of the instrument. One of the LEDs is delegated the task of flashing the color according to the state of the machine. The speed of flashing is controlled by the main run loop, which provides visual feedback that the code has not been locked. The following sections describe the states in more detail.

6.7 Start

At start-up, the mass spectrometer checks the status of all peripherals attached to the bus. Most of the peripherals, ADCs and individual power supplies can be checked by interpreting the data they provide. Any fault in the self-test causes the mass spectrometer to enter a fault mode.

6.8 Standby

In standby mode, the microprocessor shuts down all peripherals except (optionally) the ion pump and the degas heater. In this minimum power mode, the system may absorb less than 1W.

6.9 Idle

In the idle mode, the microprocessor ties the high voltage supply and the filament supply together. The filament is operated at a reduced voltage to increase its lifetime. In this mode, the microprocessor is able to ensure that the high voltage supply is working properly and that the filament is not burned. During transition to idle mode, the filament slowly warms up to reduce thermal shock. The filament warm-up time may be about 0.5 s.

6.10 Sweep (Sweep)

In the sweep mode, the microprocessor actively drives the electrodes and measures the ion current. The ion source is supplied up to a minimum voltage (approximately 150V) that can be realized by hardware and swept at about 20V/s to about 800V. The electrostatic lens voltage is also constantly changed to properly focus the ion beam at each ion source potential.

The electrometer current is sent out of the serial port to a laptop or other computing device connected to the mass spectrometer. Data can be collected by a simple terminal program; when a quality scan is run, the data is output as multi-column text that can be captured on a laptop and opened as a data file (e.g., comma separated variables (. CSV) file) in a data analysis program.

The mass spectrometer is controlled by a serial terminal interface accessed via a computer. The terminal program on the mass spectrometer allows commands to be sent and interpreted, mostly for debugging purposes, but also for controlling the state of the machine. The command "mode" with arguments specifying the new state allows the user to switch between the modes of operation as detailed above. Commands "filament", "repeller", "ion box", "lens 1", and "lens 2" with arguments such as floating point numbers or on/off (e.g., "filament off", "ion box 500.0") allow the user to directly control the electrodes in the vacuum chamber. Since the microprocessor cannot know when these features should be enabled or disabled, the other commands "degas", "ion pump" allow the user to remotely turn these peripherals on or off.

7.0 testing

The mass spectrometer was subjected to full testing of the fitting as well as the complete system.

7.1 Power and control System

All power supplies are energized and tested with respect to a nominal voltage. Particular attention will be given to the ± 2.5V analog electrometer supply because the noise figure of this supply directly affects the electrometer noise floor through the CMRR of the electrometer operational amplifier.

The control software was tested by verifying that the mass spectrometer was able to run for several days in all modes without crashing. Then, each operation mode is checked with respect to power consumption. Table 1 (below) shows the power consumption at 12VDC for each mode of operation. Note that in each mode of operation, the instrument absorbs less power than any other existing miniature mass spectrometer. The ion pump absorbs 3W, but this amount of power is not very sufficient to maintain the pump.

Table 1: mass spectrometer supply current in different modes of operation

7.2 Electron Beam

The operation of the electron beam is the first diagnostic procedure of the mass spectrometer. Operation is generally characterized by well current. The trap current is a fraction of the electron current emitted from the filament, passing completely through the ionization region, and collected at the trap electrode. The well current should be directly proportional to the filament brightness, which itself is a strongly non-linear function of the filament power. Above a certain power level, the well current starts to rise rapidly and the filament life decreases.

Filament strength as a function of filament voltage V is proportional to V ^ (3.4) and filament life is proportional to V ^ -16, which gives a strong motivation not to overdrive the filament. The filament used in this mass spectrometer was the filament of a standard PR-2 tungsten flash lamp bulb. Such bulbs are rated for a 15 hour life at 2.4V and 0.5A. Operating at a reduced voltage will increase its lifetime. For example, at 2.3V, the filament will retain 86% of its brightness, doubling its lifetime to 30 hours.

The well currents were measured at two different filament voltages and are summarized in table 2.

Table 2: well current as a function of filament voltage

The trap current may vary somewhat greatly during different experiments, dropping to 25 μ Α during some tests even at an operating voltage of 2.4V, which may cause the exact orientation of the filament with respect to the ionization region to change due to the fact that the mass spectrometer is frequently disassembled and reassembled.

7.3 degassing Heater

Fig. 20 is a diagram of a outgassing heater 2000 formed by a network of resistive heaters 2002 connected to a mass spectrometer base plate 2004, such as substrate 190 (fig. 1A) or electronics plate 1120 (fig. 11). The heater 2000 can be used to remove at least some of the gas absorbed and adsorbed on the plates by increasing the temperature of the plates. Turning on heater 2000 involves driving an electric current through resistive heater 2002, which in turn causes resistive heater 2002 and plate 2002 to heat up. As the plate 2002 heats up, it releases the absorbed and adsorbed gas that is pumped out of the vacuum chamber by the ion pump 120 (fig. 1A), a separate turbo pump attached to the vacuum chamber, or both. When the heater is operating normally, it should be possible to turn the heater on under vacuum, see the chamber pressure rising with the expelled gas, and then see the pressure dropping to a level below the initial level when the heater is turned off again.

FIG. 21 is a graph of pressure versus time for experiments run to test a degas heater. The mass spectrometer was mounted in a vacuum enclosure and evacuated. When the chamber pressure stabilized, the heater was turned on and then turned off again after approximately three hours. Note that a relatively slow initial drop in chamber pressure is followed by a rise in chamber pressure when the heater is turned on. The gas is driven out, the chamber pressure begins to drop, and then the heater is turned off at this time. At this point, the power electronics are activated, which generate their own heat and drive the gases out of the electronics board. Later, these two cycles could be performed simultaneously, but they currently generate too much heat to operate simultaneously without damage.

Fig. 22 shows infrared images of the analyzer board at different time intervals after the heater was turned on. The mass analyzer plate was placed under a thermal imaging camera (e.g., a FLIR thermography a40 camera) and transient thermal behavior was observed for ten minutes (600 s). The temperature rise was moderate in absolute value in this series of frames and the experiment was performed in air. In vacuum, there is no convection cooling the surface and the temperature rise should be substantially faster, but the heat will flow in the pattern observed here.

7.4 lens linearization

Fig. 23 shows the relative calibration of each lens driver. Although an attempt is made to ensure that the feedback control loop wrapped around each of the lens drivers is accurate, there is some degradation between the lens command and the lens voltage. Thus, the ion source potential and the two electrostatic lenses are calibrated. The calibration curve is linearized and programmed into the code of the mass spectrometer controller to ensure that the correct voltage is output to the lens. Since the lens drivers have been given the premise that they are constructed using the same hardware, they differ by several volts, although they are similar. This may seem less important, but the potential energy surfaces described above represent how some of these voltages should be carefully aligned; improperly tuned lenses can severely limit or block the ion beam, causing the signal to cancel.

7.5 ion Pump

The small, co-produced ion pump was tested on its own after the system had been pumped to 2.6e-6Pa [2.0e-8 Torr ]. The ion pump was started at 2.6e-4Pa [2.0e-6 Torr ] and operated in conjunction with the turbo pump of the vacuum chamber until the pressure reached 2.6e-6Pa, at which time the valve interposed between the turbo pump and the chamber was closed.

Figures 24 and 25 are graphs of vacuum chamber pressure, pump voltage, and ion current during the commissioning process. First, the mini-ion pump is heated to drive out the absorbed gas and operated in conjunction with a second high vacuum pump until the ion pump is ready to carry a gas load. This commissioning process takes approximately 15 hours without the use of the on-board heater of the mass spectrometer.

Fig. 26 includes photographs of ion pumps disassembled after a commissioning test. A titanium cathode plate was recessed in the center of each pump cell and the anode was plated with sputtered titanium.

7.6 Mass Spectrometry

For the mass spectrometer of the present invention, the spectra may be expressed as a change in ion beam current with ion source potential. Although the microprocessor may be programmed to output ion current versus mass to charge ratio, for this example, mapping between ion source potential and m/z is performed at the time of data post-processing. Alternatively, the mass spectrometer of the present invention can measure high voltage bias parameters (e.g., filament current, trap current).

A number of mass sweep tests were run on the miniature mass spectrometer. Between tests, a number of optimizations are made based on the resulting data. The optimization is typically minimal and includes adjusting variable geometry mass analyzer slits and electrometer hardware (e.g., feedback resistors, capacitors) and modifying software to optimize filament power, electrostatic lens potential, and ion source voltage sweep speed and range.

Fig. 27 shows a mass spectrum collected from an exemplary compact mass spectrometer. The large central peak may be nitrogen, while the peak on the right side of the figure is water. Oxygen may appear as a peak protruding from the left shoulder of the nitrogen peak; this example mass spectrometer does not have sufficient resolution to separate masses that are 4AMU apart. This spectrum shows that a digital controller has been used to adjust one of the electrodes to cut (chop) the ion beam.

Figure 28 is a mass spectrum captured by another version of the mass spectrometer highlighting the prominent peaks. The data have been corrected for the inverse relationship between acceleration potential and mass/charge ratio. Note the peak at 29m/z, which is likely an isotope of nitrogen, 15N14N, which is present in air at 0.36% abundance relative to 14N 14N.

One interesting feature observed is that even if the electrostatic lens is disabled (e.g., the lens is programmed not to change the ion beam), the mass spectrometer operates despite having a lower signal-to-noise ratio. This result was used to characterize the effect of the electrostatic lens.

Fig. 29 is a pair of spectra, one operating with the lens off and the other operating with the lens on. The lens gives a nearly tenfold increase in signal strength without increasing the noise floor. This is extremely valuable in mass spectrometers and shows how a much stronger signal can be produced for capturing and analyzing a larger fraction of the generated ions. Initially adjust the lens by hand; the ion source is set to a potential with a known ion species and then the lens is adjusted to obtain the maximum signal. Several ions were conditioned and the resulting curves were fitted with linear interpolations.

Fig. 30 is a mass spectrum of air showing the effect of the variable geometry slit. The salient features of this comparison are visible at the bottom of the peak, although several other factors, including the overall gain of the system, have changed. The peaks of m/z 27 and 26 are both visible in the red curve given with the narrower slit, while they are not visible at all in the blue curve given with the wider slit.

FIG. 31 is a graph showing a property spectrometer capable of detecting new species entering the inlet. Fig. 31 is a test of the detectability of the mass spectrometer. Nitrous oxide (N)₂O) was injected into the inlet and a mass spectral sweep was run. Control runs show the standard spectrum in blue; water, nitrogen, oxygen. The run containing nitrous oxide showed several new peaks. N is a radical of₂O is very clearly shown at m/z 44 and another species (fragmented ion NO) is revealed between oxygen and nitrogen at m/z 30.

FIG. 32 is a series of spectra generated using a gate as a tuning source. The grid (control electrode) of the ion source is used to remove the background drift or 1/f noise of the electrometer. The blue curve is the baseline curve, which is generated when the grid is biased such that the electron beam is truncated. The red curve is the signal curve, which is generated when the ion beam is enabled. The green curve is the subtraction of the two and is the signal with the baseline biased and drift removed.

These figures illustrate the mass spectrometer of the present invention with a resolution that is adequate for many tasks including, but not limited to, use as a medical tool, environmental tool, or industrial tool. In at least one instance, experimental results indicate that the mass spectrometer is sufficiently sensitive to detect species that constitute less than 0.5% of the incoming sample gas, and has a mass resolution of 1 AMU. As indicated on the graph in fig. 28, the noise floor is quite low, below 10 fA. Deconvolution with an appropriate function may produce an even narrower spectrum.

8.0 conclusion

While various embodiments of the invention have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the functions and/or obtaining the results and/or advantages described herein, and each of the above-described variations and/or modifications is deemed to be within the scope of the embodiments of the invention described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the teachings of the present invention is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the foregoing embodiments are provided merely as examples and that, within the scope of the appended claims and equivalents thereto, embodiments of the invention may be practiced otherwise than as specifically described or claimed. The presently disclosed embodiments of the invention are directed to each individual feature, system, article, material, tool and/or method described herein. Moreover, any combination of two or more such features, systems, articles, materials, tools, and/or methods, if such features, systems, articles, materials, tools, and/or methods are not mutually inconsistent, is included within the scope of the present disclosure.

The above-described embodiments may be implemented in any of numerous ways. For example, the embodiments may be implemented using hardware, software, or a combination of hardware and software. When implemented in software, the software code can run on any suitable processor or group of processors, whether arranged on a single computer or distributed among multiple computers.

Further, it should be appreciated that a computer may be embodied in any of a variety of forms, such as a rack-mounted computer, a desktop computer, a portable computer, or a tablet computer. Further, a computer may be embedded in a device not normally considered a computer, but having suitable processing capabilities, such devices including Personal Digital Assistants (PDAs), smart phones, or any other suitable portable or fixed electronic device.

In addition, a computer may have one or more input devices. In addition to this, these devices can be used to present a user interface. Examples of output devices that can be used to provide a user interface include printers or display screens for visual presentation of output and speakers or other sound generating devices for audible presentation of output. Examples of input devices that can be used for a user interface include keyboards, and pointing devices, such as mice, touch pads, and digitizing tablets. As another example, a computer may receive input information through speech recognition or in other audible format.

Such computers may be interconnected by one or more networks IN any suitable form, including as local area networks or wide area networks, such as an enterprise network and an Intelligent Network (IN) or the Internet. Such networks may be based on any suitable technology and may operate according to any suitable protocol, and may include wireless networks, wired networks, or fiber optic networks.

The various methods or processes outlined herein may be coded as software that is executable on one or more processors that employ any one of a variety of operating systems or platforms. Further, such software may be written using any of a number of suitable programming languages and/or programming or scripting tools, and may also be compiled as executable machine language code or intermediate code that runs on a framework or virtual machine.

In this regard, the concepts of the present invention may be embodied as a computer readable storage medium (or multiple computer readable storage media) encoded with one or more programs, such as a computer memory, one or more pieces of software, optical disks, magnetic tapes, flash memories, circuit configurations in field programmable gate arrays or other semiconductor devices, or other non-transitory or tangible computer storage media, that perform methods that implement the embodiments of the invention discussed above when the one or more programs are run on one or more computers or other processors. The computer readable medium or media can be transportable, such that the program or programs stored thereon can be loaded onto one or more different computers or other processors to implement various aspects of the present invention as discussed above.

The terms "program" or "software" are used herein in a generic sense to refer to any type of computer code or set of computer-executable instructions that can be employed to program a computer or other processor to implement various aspects of the embodiments discussed above. Furthermore, it should be appreciated that according to one aspect, one or more computer programs that when executed perform methods of the present invention need not reside on a single computer or processor, but may be distributed in a modular fashion amongst a number of different computers and processors to implement various aspects of the present invention.

Computer-executable instructions may take many forms, such as program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Typically, the functionality of the program modules may be combined or distributed as desired in various embodiments.

In addition, the data structures may be stored in any suitable form on a computer readable medium. To simplify the illustration, the data structure may be shown as having fields associated with the location of the data structure. Such relationships may likewise be obtained by allocating storage space for the fields with locations in the computer-readable medium that convey relationships between the fields. However, any suitable mechanism may be used to establish relationships between information in fields of a data structure, including through the use of pointers, tags, or other mechanisms that establish relationships between data elements.

Furthermore, the concepts of the invention may be embodied as one or more methods, examples of which have been provided. The actions performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts concurrently, although shown as sequential acts in the illustrative embodiments.

All definitions defined and used herein should be understood to assemble dictionary definitions, definitions in documents incorporated by reference, and/or the ordinary meaning of the defined terms.

The indefinite articles "a" and "an" as used herein in the specification and in the claims are to be understood as meaning "at least one" unless expressly stated to the contrary.

The phrase "and/or" as used herein in the specification and in the claims should be understood to mean "either or both" of the elements so combined, i.e., elements that are present in combination in some cases and in isolation in other cases. Multiple elements listed with "and/or" should be interpreted in the same manner, i.e., "one or more" of the elements so combined. There may optionally be additional elements other than the elements specifically identified by the "and/or" phrase, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, when a reference to "a and/or B" is used in conjunction with an open language such as "comprising," the reference to "a and/or B" can refer, in one embodiment, to only a (optionally including elements other than B), in another embodiment, to only B (optionally including elements other than a), in yet another embodiment to both a and B (optionally including other elements), and so forth.

As used herein in the specification and claims, "or" is to be understood as having the same meaning as "and/or" as defined above. For example, when "or" and/or "separates items in a list," or "and/or" should be interpreted as being inclusive, i.e., including at least one of the plurality of elements or the series of elements, but also including more than one element, and optionally including additional unlisted items. Only items explicitly specified to the contrary, such as "only one of …" or "exactly one of …", or "consisting of …" when used in the claims, will be referred to as including a plurality or exactly one of the series of elements. In general, the term "or", as used herein, when preceded by an exclusive term such as "or … … (either)", "one of …", "only one of …", or "exactly one of …", should be construed to mean only an exclusive choice (i.e., "one or the other, but not both"). "consisting essentially of …" which, when used in the claims, shall have the ordinary meaning used in the patent law field.

The phrase "at least one of," as used herein in the specification and in the claims, in reference to a series of one or more elements, should be understood to mean at least one element selected from any one or more of the series of elements, but not necessarily including at least one of each element specifically listed in the series of elements and not excluding any combinations of elements in the series of elements. The definition also allows that optionally there may be elements other than the specifically identified elements in the series of elements to which the phrase "at least one" refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, "at least one of a and B" (or, equivalently, "at least one of a or B" or, equivalently "at least one of a and/or B") can: in one embodiment, to at least one, optionally including more than one, a, with no B present (and optionally including elements other than B); in another embodiment, to at least one B, optionally including more than one B, with no a present (and optionally including elements other than a); in yet another embodiment, to at least one a and at least one B, optionally including more than one a, and optionally including more than one B (and optionally including other elements); and so on.

In the claims, as well as in the specification above, all transitional phrases such as "comprising," "including," "carrying," "having," "containing," "involving," "holding," "covering," and the like are to be understood to be open-ended, i.e., to mean including but not limited to. The transitional phrases "consisting of …" and "consisting essentially of …" should be closed or semi-closed transitional phrases, respectively, as mentioned in section 2111.03 of the U.S. patent office patent examination program manual.

Claims (56)

1. A mass spectrometer, comprising:

(A) vacuum envelope defining a support 10^-5A vacuum chamber of mm Hg or less;

(B) an electrode disposed in the vacuum chamber and configured to be charged to an electrode potential to control acceleration of charged particles propagating through the vacuum chamber;

(C) a switching circuit arranged in the vacuum chamber to switch an input voltage from a power source outside the vacuum chamber so as to provide the electrode potential to the electrode;

(D) a feedthrough having a dielectric strength of less than or equal to 36V to provide an electrical connection between the conversion circuit and the power source;

(E) control electronics disposed in the vacuum chamber and operably coupled to the switching circuit to vary the electrode potential; and

(F) a heater operably coupled to the control electronics and in thermal communication with at least one component within the vacuum chamber to heat the at least one component in response to a signal from the control electronics so as to drive gas out of the at least one component,

wherein the control electronics comprise at least one digital-to-analog converter for setting the electrode potential of the electrodes.

2. A mass spectrometer, comprising:

(A) vacuum envelope defining a support 10^-5A vacuum chamber of mm Hg or less;

(B) an electrode disposed in the vacuum chamber and configured to be charged to an electrode potential to control acceleration of charged particles propagating through the vacuum chamber;

(C) a switching circuit arranged in the vacuum chamber to switch an input voltage from a power source outside the vacuum chamber so as to provide the electrode potential to the electrode;

(D) a feedthrough having a dielectric strength of less than or equal to 36V to provide an electrical connection between the conversion circuit and the power source;

(E) control electronics disposed in the vacuum chamber and operably coupled to the switching circuit to vary the electrode potential; and

(F) a heater operably coupled to the control electronics and in thermal communication with at least one component within the vacuum chamber to heat the at least one component in response to a signal from the control electronics so as to drive gas out of the at least one component,

wherein the heater comprises a network of resistive heating elements arranged on a substrate.

3. A mass spectrometer, comprising:

(A) vacuum envelope defining a support 10^-5A vacuum chamber of mm Hg or less;

(B) an electrode disposed in the vacuum chamber and configured to be charged to an electrode potential to control acceleration of charged particles propagating through the vacuum chamber;

(C) a switching circuit arranged in the vacuum chamber to switch an input voltage from a power source outside the vacuum chamber so as to provide the electrode potential to the electrode;

(D) a feedthrough having a dielectric strength of less than or equal to 36V to provide an electrical connection between the conversion circuit and the power source;

(E) control electronics disposed in the vacuum chamber and operably coupled to the switching circuit to vary the electrode potential;

(F) a heater operably coupled to the control electronics and in thermal communication with at least one component within the vacuum chamber to heat the at least one component in response to a signal from the control electronics so as to drive gas out of the at least one component; and

(G) an ion pump disposed within the vacuum chamber to pump the gas out of the vacuum chamber in order to maintain the 10^-5A vacuum of mm Hg or less.

4. A mass spectrometer, comprising:

(A) vacuum envelope defining a support 10^-5A vacuum chamber of mm Hg or less;

(B) an electrode disposed in the vacuum chamber and configured to be charged to an electrode potential to control acceleration of charged particles propagating through the vacuum chamber;

(C) a switching circuit arranged in the vacuum chamber to switch an input voltage from a power source outside the vacuum chamber so as to provide the electrode potential to the electrode;

(D) a feedthrough having a dielectric strength of less than or equal to 36V to provide an electrical connection between the conversion circuit and the power source;

(E) control electronics disposed in the vacuum chamber and operably coupled to the switching circuit to vary the electrode potential;

(F) a heater operably coupled to the control electronics and in thermal communication with at least one component within the vacuum chamber to heat the at least one component in response to a signal from the control electronics so as to drive gas out of the at least one component; and

(G) a wireless communication interface operably coupled to the control electronics to relay data and instructions between an interior of the vacuum chamber and an exterior of the vacuum chamber.

5. A mass spectrometer, comprising:

(A) a vacuum enclosure defining a vacuum chamber;

(B) a magnet located in a yoke defining at least one gap, the magnet for generating a magnetic field having a first strength in a first region within the at least one gap and a second strength in a second region within the at least one gap;

(C) an ion pump positioned in the first region within the at least one gap to maintain a vacuum pressure of the vacuum chamber;

(D) a mass analyzer positioned in the second region within the at least one gap to determine a mass of ionized analyte particles propagating through the vacuum chamber;

(E) a control electrode disposed in the vacuum chamber to control acceleration of electrons ionizing the analyte particles;

(F) a switching circuit arranged in the vacuum chamber to provide a switched voltage to the ion pump, the control electrode and/or the mass analyser;

(G) control electronics disposed in the vacuum chamber and operably coupled to the switching circuit to vary a potential of the control electrode; and

(H) a heater operably coupled to the control electronics and in thermal communication with at least one component within the vacuum chamber to heat the at least one component in response to a signal from the control electronics so as to drive gas out of the at least one component,

wherein the control electronics comprise at least one digital-to-analog converter for setting the electrode potential of the electrodes.

6. A mass spectrometer, comprising:

(A) a vacuum enclosure defining a vacuum chamber;

(B) a magnet located in a yoke defining at least one gap, the magnet for generating a magnetic field having a first strength in a first region within the at least one gap and a second strength in a second region within the at least one gap;

(C) an ion pump positioned in the first region within the at least one gap to maintain a vacuum pressure of the vacuum chamber;

(D) a mass analyzer positioned in the second region within the at least one gap to determine a mass of ionized analyte particles propagating through the vacuum chamber;

(E) a control electrode disposed in the vacuum chamber to control acceleration of electrons ionizing the analyte particles;

(F) a switching circuit arranged in the vacuum chamber to provide a switched voltage to the ion pump, the control electrode and/or the mass analyser;

(G) control electronics disposed in the vacuum chamber and operably coupled to the switching circuit to vary a potential of the control electrode; and

(H) a heater operably coupled to the control electronics and in thermal communication with at least one component within the vacuum chamber to heat the at least one component in response to a signal from the control electronics so as to drive gas out of the at least one component,

wherein the heater comprises a network of resistive heating elements arranged on a substrate.

7. A mass spectrometer, comprising:

(A) a vacuum enclosure defining a vacuum chamber;

(B) a magnet located in a yoke defining at least one gap, the magnet for generating a magnetic field having a first strength in a first region within the at least one gap and a second strength in a second region within the at least one gap;

(C) an ion pump positioned in the first region within the at least one gap to maintain a vacuum pressure of the vacuum chamber;

(D) a mass analyzer positioned in the second region within the at least one gap to determine a mass of ionized analyte particles propagating through the vacuum chamber;

(E) a control electrode disposed in the vacuum chamber to control acceleration of electrons ionizing the analyte particles;

(F) a switching circuit arranged in the vacuum chamber to provide a switched voltage to the ion pump, the control electrode and/or the mass analyser;

(G) control electronics disposed in the vacuum chamber and operably coupled to the switching circuit to vary a potential of the control electrode;

(H) a heater operably coupled to the control electronics and in thermal communication with at least one component within the vacuum chamber to heat the at least one component in response to a signal from the control electronics so as to drive gas out of the at least one component; and

(I) a wireless communication interface operably coupled to the control electronics to relay data and instructions between an interior of the vacuum chamber and an exterior of the vacuum chamber.

8. A mass spectrometer, comprising:

a vacuum enclosure defining a vacuum chamber maintained within10^-5A pressure of mm Hg or less;

an electrode disposed in the vacuum chamber and configured to be charged to an electrode potential to control acceleration of charged particles propagating through the vacuum chamber;

a digital controller disposed in the vacuum chamber and in electrical communication with the electrode to control the electrode potential at the electrode; and

a heater in thermal communication with at least one component within the vacuum chamber to heat the at least one component to drive gas out of the at least one component.

9. The mass spectrometer of claim 8,

the electrodes include gate electrodes to control the flow of electrons; and is

The digital controller is configured to modulate the electrode potential at the gate electrode.

10. The mass spectrometer of claim 9, further comprising:

signal processing electronics operably coupled to the digital controller to process a digital controller signal for modulating the electrode potential at the gate electrode so as to improve the signal-to-noise ratio of the mass spectrometer.

11. The mass spectrometer of claim 10, wherein the signal processing electronics are configured to process the digital controller signal using a synchronous detection signal processing technique and/or a stochastic system identification signal processing technique.

12. The mass spectrometer of claim 8, further comprising:

a communication module disposed in the vacuum chamber and operably coupled to the digital controller to relay data and/or instructions between the digital controller and at least one electronic component located outside the vacuum chamber.

13. The mass spectrometer of claim 12, wherein the communication module comprises a wireless communication interface configured to send and/or receive data and/or instructions via at least one wireless communication channel.

14. The mass spectrometer of claim 12, wherein the communication module is configured to relay the data and/or instructions via at least one data line fed through at least one wall of the vacuum enclosure.

15. The mass spectrometer of claim 8, wherein:

the electrodes comprise electrostatic lens electrodes configured to focus a stream of ionized particulates; and is

The digital controller is configured to control the electrode potential of the electrostatic lens electrode.

16. The mass spectrometer of claim 15, wherein the electrostatic lens electrode focuses the stream of ionized particulates onto at least one aperture to limit diffusion of the stream of ionized particulates.

17. The mass spectrometer of claim 16, wherein the at least one aperture is defined by at least one member formed by a housing of a mass analyzer.

18. The mass spectrometer of claim 17, wherein the at least one member comprises a flexure to vary a width of the at least one aperture.

19. The mass spectrometer of claim 8, wherein the heater comprises a network of resistive heating elements arranged on a substrate.

20. A method for mass spectrometry analysis, the method comprising:

(A) maintained 10 within a vacuum chamber defined by a vacuum enclosure^-5A pressure of mm Hg or less;

(B) charging an electrode disposed within the vacuum chamber to an electrode potential so as to control acceleration of charged particles propagating through the vacuum chamber;

(C) controlling the electrode potential at the electrode via a digital controller disposed in the vacuum chamber and in electrical communication with the electrode; and

(D) heating at least one component within the vacuum chamber to drive gas out of the at least one component.

21. The method of claim 20, wherein:

(B) comprising charging a gate electrode configured to control a flow of electrons; and is

(C) Comprising modulating the electrode potential at the gate electrode.

22. The method of claim 21, further comprising:

(E) processing a digital controller signal for modulating the electrode potential at the gate electrode so as to improve the signal-to-noise ratio of the mass spectrometer.

23. The method of claim 22, wherein (E) comprises processing the digital controller signal using a synchronous detection signal processing technique and/or a stochastic system identification signal processing technique.

24. The method of claim 20, further comprising:

(F) relaying data and/or instructions between the vacuum chamber and outside of the vacuum chamber via a communication module coupled to the digital controller.

25. The method of claim 24, wherein (F) comprises relaying data and/or instructions with a wireless communication interface configured to transmit and/or receive data and/or instructions via at least one wireless communication channel.

26. The method of claim 24, wherein (F) comprises relaying data and/or instructions via at least one data line fed through at least one wall of the vacuum enclosure.

27. The method of claim 20, wherein:

(B) comprising charging an electrostatic lens electrode to focus a stream of ionized particles; and is

(C) Comprising controlling an electrode potential of the electrostatic lens electrode.

28. The method of claim 27, further comprising:

focusing the stream of ionized particles onto at least one aperture to limit diffusion of the stream of ionized particles.

29. The method of claim 28, wherein the at least one aperture is defined by a housing of a mass analyzer.

30. The method of claim 29, further comprising varying a width of the at least one aperture.

31. The method of claim 20, wherein heating the at least one component comprises heating the at least one component with a heater comprising a network of resistive heating elements arranged on a substrate.

32. A mass spectrometer, comprising:

a vacuum enclosure defining a vacuum chamber;

an inlet in fluid communication with the vacuum chamber to allow introduction of a gaseous sample into the vacuum chamber for mass spectrometry;

an electron source disposed within the vacuum chamber to generate electrons that ionize particles of the gaseous sample so as to form ions;

a gate electrode disposed within the vacuum chamber and configured to be charged to a gate electrode potential to control acceleration of the electrons that ionize particles of the gaseous sample;

an electrostatic lens system disposed within the vacuum chamber and comprising:

an electrostatic lens electrode configured to be charged to an electrostatic lens electrode potential to focus the ions into an ion beam;

at least one aperture defined by a mass spectrometer assembly to focus the ion beam;

at least one flexure integral with the mass spectrometer assembly to vary a width of the at least one aperture;

a digital controller disposed within the vacuum chamber and in electrical communication with the gate electrode and/or the electrostatic lens electrode to control and/or modulate the gate electrode potential and/or control the electrostatic lens electrode potential; and

a heater in thermal communication with at least one component within the vacuum chamber to heat the at least one component to drive gas out of the at least one component.

33. A mass spectrometer, comprising:

a vacuum enclosure defining a vacuum chamber;

an electrode disposed within the vacuum chamber and configured to be charged to an electrode potential to control acceleration of charged particles propagating through the vacuum chamber;

a controller disposed within the vacuum chamber and in electrical communication with the electrode to modulate the electrode potential at the electrode; and

a processor operably coupled to the controller to process a digital controller signal for modulating the electrode potential so as to improve a signal-to-noise ratio of the mass spectrometer.

34. The mass spectrometer of claim 33, wherein the electrode comprises a gate electrode.

35. The mass spectrometer of claim 33, wherein the charged particles are ions.

36. The mass spectrometer of claim 33, wherein the charged particles are electrons.

37. The mass spectrometer of claim 36, further comprising:

an electron source disposed within the vacuum chamber to provide the electrons;

a cathode for repelling the electrons; and

an anode disposed opposite the electrode, remote from the electron source, to accelerate the electrons toward analyte particles to be analyzed.

38. The mass spectrometer of claim 36, further comprising:

a switching circuit disposed within the vacuum chamber to provide:

(i) an anode potential of 100V to 5kV for the anode; and

(ii) a cathode potential for the cathode of 70V below the anode potential, and

wherein the electrode potential is between 0V and 140V below the anode potential.

39. The mass spectrometer of claim 33, wherein the processor is configured to perform at least one of synchronous detection and stochastic system identification.

40. The mass spectrometer of claim 33, wherein the processor is configured to perform calibration in accordance with the digital controller signal used to modulate the electrode potential.

41. The mass spectrometer of claim 33, wherein the controller comprises:

at least one digital-to-analog converter for setting the electrode potential.

42. The mass spectrometer of claim 33, wherein the controller comprises:

a Radio Frequency (RF) communication module disposed within the vacuum chamber and operably coupled to the processor to relay data and/or instructions between the interior and exterior of the vacuum enclosure.

43. A method of operating a mass spectrometer, the method comprising:

is provided to be evacuated to 10^-5A vacuum chamber at a pressure of mm Hg or less;

charging an electrode within the vacuum chamber to an electrode potential;

modulating the electrode potential so as to control acceleration of charged particles within the vacuum chamber; and

processing a digital controller signal for modulating the electrode potential to improve the signal-to-noise ratio of the mass spectrometer.

44. The method of claim 43, wherein modulating the electrode potential comprises generating the digital controller signal with a controller disposed within the vacuum chamber.

45. The method of claim 43, wherein modulating the electrode potential comprises applying the electrode potential to a gate electrode.

46. The method of claim 43, wherein modulating the electrode potential comprises setting the electrode potential with at least one digital-to-analog converter disposed within the vacuum chamber.

47. The method of claim 43, wherein the charged particles are ions.

48. The method of claim 43, wherein the charged particles are electrons.

49. The method of claim 48, further comprising:

providing said electrons using an electron source;

accelerating the electrons towards the analyte particles; and

detecting the analyte particles.

50. The method of claim 48, wherein modulating the electrode potential comprises:

generating a voltage with a conversion circuit disposed within the vacuum chamber; and

applying the voltage to the electrode.

51. The method of claim 43, wherein processing the digital controller signal includes performing at least one of synchronous detection and random system identification.

52. The method of claim 43, further comprising:

relaying data and/or instructions between the interior and exterior of the vacuum enclosure with a radio frequency communication module disposed within the vacuum chamber.

53. The method of claim 43, further comprising:

calibrating the mass spectrometer in accordance with the digital controller signal for modulating the electrode potential.

54. A mass spectrometer, comprising:

a vacuum enclosure defining a vacuum chamber;

a magnet located in the yoke, the magnet for generating a magnetic field having a first strength in a first region and a second strength in a second region;

an ion pump disposed in the first region to maintain a vacuum pressure of the vacuum chamber;

a mass analyzer disposed in the second region to determine a mass of ionized analyte particles propagating through the vacuum chamber;

a control electrode disposed in the vacuum chamber to control acceleration of electrons ionizing the analyte particles;

a switching circuit arranged in the vacuum chamber to provide a switched voltage to the ion pump, the control electrode and/or the mass analyser;

control electronics disposed in the vacuum chamber and operably coupled to the switching circuit to modulate a potential of the control electrode; and

signal processing electronics disposed within the vacuum chamber and configured to be powered by the conversion circuitry to process a signal provided by the mass analyzer.

55. A mass spectrometer of claim 54, wherein the magnets in the yoke are configured such that the first strength is 0.1 Tesla and the second strength is 0.7 Tesla when the magnetic field is generated.

56. The mass spectrometer of claim 54, in which the conversion circuit is configured to provide a converted voltage from an input voltage, the converted voltage having a first value of 100V to 5kV, the input voltage having a second value of 1V to 36V.