WO2010090957A2

WO2010090957A2 - Electrospray ionization utilizing auxiliary gas

Info

Publication number: WO2010090957A2
Application number: PCT/US2010/022652
Authority: WO
Inventors: Mingda Wang; Joseph S. Saba
Original assignee: Varian Inc
Current assignee: Varian Inc
Priority date: 2009-02-03
Filing date: 2010-01-29
Publication date: 2010-08-12
Anticipated expiration: 2011-08-03
Also published as: WO2010090957A3

Abstract

An electrospray ionization device includes a sample conduit providing a sample flow path in a sample flow direction; a first gas conduit surrounding the sample conduit and having an annular outlet; a support structure surrounding the sample conduit; a housing surrounding the sample conduit and includes a first end at the support structure and an axially opposite open second end; and a second gas conduit. The first gas conduit provides a first gas flow path in the sample flow direction. The second gas conduit has a second gas inlet and a second gas outlet in open communication with the housing and provides a second gas flow path from the second gas outlet into the housing that is in the sample flow direction, surrounds the sample conduit and is constrained in a radial direction by the housing.

Description

ELECTROSPRAY IONIZATION UTILIZING AUXILIARY GAS

PRIORITY CLAIM

[0001] This application claims priority from U.S. Provisional Patent Application Serial No. 61/149,597, filed February 3, 2009, titled "ELECTROSPRAY ION SOURCE WITH HEATED AUXILIARY VORTEX GAS".

FIELD OF THE INVENTION

[0002] The present invention relates generally to the ionization of molecules, which finds use for example in fields of analytical chemistry such as mass spectrometry (MS). More particularly, the invention relates to improving heat transfer to droplets discharged from an electrospray ionization (ESI) device.

BACKGROUND OF THE INVENTION [0003] Figure 1 is a partially cross-sectional view of an example of a part of a mass spectrometry (MS) system 100 that includes a known atmospheric pressure ionization (API) interface 102. Generally, the API interface 102 receives a liquid sample, ionizes it, and transmits it to a mass analyzer (not shown) in a manner familiar to persons skilled in the art. The API interface 102 is advantageous because in addition to performing the required ionization, it provides an interface between the ambient or pressurized environment in which the liquid sample originates and the vacuum environment in which mass analyzers and their associated ion detectors process ions effectively.

[0004] An electrospray ionization (ESI) device 104 extends into an ionization chamber 106. The ESI device 104 includes a sample conduit 108 and a nebulizing gas conduit 110 extending from a support structure 112. The sample conduit 108 is typically provided in the form of a capillary tube, also termed an electrospray needle. A liquid sample flows through the sample conduit 108 along a sample conduit axis 114 to an open sample conduit tip 116. While the liquid sample flows through the sample conduit 108, a voltage potential is applied between sample conduit 108 (typically at or near the sample conduit tip 116) and an appropriately positioned counter-electrode, such as a conductive surface in the ionization chamber 106. The electric field established by this voltage potential induces charge accumulation at the surface of the liquid sample at the sample conduit tip 116. Consequently, the liquid sample is discharged from the sample conduit tip 116 in a sample flow direction 118 as a spray or stream of charged droplets, or electrospray. Nebulizing gas (e.g., nitrogen) flows through the nebulizing gas conduit 110 to a nebulizing gas outlet typically located at or near the sample conduit tip 116. The nebulizing gas assists in nebulizing the liquid sample such that the electrospray is formed as a fine mist.

[0005] Figure 2 is a cross-sectional view of an example of the region of the ESI device 104 at the sample conduit tip 116. In this example, the nebulizing gas conduit 110 is coaxial to the sample gas conduit 108 and terminates at a nebulizing gas outlet 212 located a short axial distance before the sample conduit tip 116. The nebulizing gas conduit 110 thus has an annular cross-section surrounding the sample gas conduit 108, and the nebulizing gas flows along a cylindrical-shaped path sharing the same axis as the sample conduit axis 114.

[0006] Referring back to figure 1, the MS system 100 further includes an interface capillary 120 that fluidly interconnects the ionization chamber 106 to a downstream mass analyzer (not shown). The sample conduit tip 116 of the ESI device 104 may be generally aimed toward a sampling orifice 122 of the interface capillary 120. Typically, the liquid sample is supplied to the ESI device 104 in the form of a matrix consisting of the molecules to be investigated (analytes) and one or more solvents, and possibly other non-analytical components. The electrospray formed at the sample conduit tip 116 is directed toward the sampling orifice 122. As the electrospray droplets flow between the sample conduit tip 116 and the interface capillary 120 they undergo a desolvation (or ion evaporation) process. As the solvent contained in the droplets evaporates the droplets become smaller, and they may rupture and divide into even smaller droplets as a result of repelling coulombic forces approaching the cohesion forces of the droplets. Eventually, analyte ions deborb from the surfaces of the droplets and a gaseous, ion-enriched stream enters the interface capillary 120. The electrospray ions and some of the droplets are drawn into the sampling orifice 122 and flow through the interface capillary 120 under the influence of the pressure differential between the ionization chamber 106 (at or around atmospheric pressure) and the very low pressure and vacuum stages of the downstream mass analyzing portion of the MS system 100. A heater (not shown) may be provided to assist in evaporating the droplets while they flow through the interface capillary 120. Additionally or alternatively, drying gas 124 (e.g., nitrogen) may be supplied from a conduit 126 and caused to flow in a counter-flow or cross-flow relation to the electrospray as the electrospray flows to the sampling orifice 122. The drying gas may assist in desolvating the charged droplets and in deflecting uncharged droplets away from the sampling orifice 122.

[0007] Despite the use of a drying gas, a curtain gas or the like, or a heater in thermal contact with the interface capillary 120 leading into the mass analyzer, there remains an ongoing need for improving the analytical quality of electrospray and consequently the performance of a mass spectrometer. Specific areas of improvement include enhancing or increasing the evaporation of liquid in the electrospray, the desolvation of cluster ions in the electrospray, the efficiency with which gas-phase ions are formed from the electrospray, and the separation of ions from liquid droplets and matrix background. Improvements in one or more of these areas would result in increasing the ion signal provided to the mass analyzer, lowering chemical background in the ion signal, and/or decreasing contamination of the mass analyzer with non-analytical components.

SUMMARY OF THE INVENTION

[0008] To address the foregoing problems, in whole or in part, and/or other problems that may have been observed by persons skilled in the art, the present disclosure provides methods, processes, systems, apparatus, instruments, and/or devices, as described by way of example in implementations set forth below.

[0009] According to one implementation, an electrospray ionization device includes a sample conduit, a first gas conduit, a support structure, a housing, and a second gas conduit. The sample conduit includes a sample conduit tip and provides a liquid sample flow path in a sample flow direction. The first gas conduit surrounds the sample conduit and includes an annular first gas outlet. The first gas conduit provides a first gas flow path in the sample flow direction. The support structure surrounds the sample conduit. The housing surrounds the sample conduit and includes a first end at the support structure and an axially opposite open second end. The second gas conduit includes a second gas inlet and a second gas outlet in open communication with the housing. The second gas conduit is configured to provide a second gas flow path from the second gas outlet into the housing that is in the sample flow direction, surrounds the sample conduit and is constrained in a radial direction by the housing. [0010] According to another implementation, a method is provided for forming gas phase ions from a liquid sample. The liquid sample is flowed through a sample conduit to a sample conduit tip. An electric field is applied at the sample conduit tip in an ionization chamber surrounding the sample conduit tip, wherein the liquid sample flows from the sample conduit tip into the ionization chamber as a stream of electrically charged droplets. A first gas is flowed around the sample conduit tip in the direction of the droplet stream to nebulize the droplets. A second gas is flowed in the direction of the droplet stream along a second gas path running between the sample conduit and a housing located in the ionization chamber and surrounding the sample conduit, wherein the second gas transfers heat to the droplets to promote evaporation of liquid and formation of gas phase ions.

[0011] Other devices, apparatus, systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS [0012] The invention can be better understood by referring to the following figures. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the figures, like reference numerals designate corresponding parts throughout the different views.

[0013] Figure 1 is a partially cross-sectional view of an example of a part of a mass spectrometry (MS) system that includes a known atmospheric pressure ionization (API) interface.

[0014] Figure 2 is a cross-sectional view of an example of a capillary tip region of a known electrospray ionization (ESI) device.

[0015] Figure 3 is cross-sectional view of an example of an ESI device according to an implementation of the present disclosure. [0016] Figure 4 is cross-sectional view of another example of an ESI device according to an implementation of the present disclosure.

[0017] Figure 5 is cross-sectional view of another example of an ESI device according to an implementation of the present disclosure.

[0018] Figure 6 is cross-sectional view of another example of an ESI device according to an implementation of the present disclosure. [0019] Figure 7 is cross-sectional view of another example of an ESI device according to an implementation of the present disclosure.

[0020] Figure 8 is cross-sectional view of another example of an ESI device according to an implementation of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

[0021] The present disclosure describes various implementations of an ESI device configured to provide a first gas and a second gas. The first gas may function as a nebulizing gas in the known manner described above. The second gas functions as an auxiliary or supplemental gas that interacts with the electrospray. Like the first gas, the second gas may be any chemically inert gas such as, for example, nitrogen. The ESI device is configured to introduce the second gas into the ionization chamber in a manner that promotes (assists, enhances, quickens, improves, increases, etc.) the evaporation of liquid in the electrospray, the desolvation of cluster ions in the electrospray, the efficiency with which gas-phase ions are formed from the electrospray, and the separation of ions from liquid droplets and matrix background. In particular, the ESI device promotes fast evaporation of droplets near its electrospray tip where the high-strength electrical field is located. These actions may be promoted by flowing the second gas along paths configured as described below, and by transferring heat from the second gas to the electrospray. To enhance the transfer of heat energy, the second gas may be heated to a temperature ranging, for example, from room temperature to 600⁰C depending on such factors as the velocity of the liquid sample flow and the characteristics of the analyte and the solvent. The second gas flows into the ionization chamber along a second flow path configured to substantially prolong the time of contact between the sample droplets, the first gas and the second gas, thereby optimizing heat transfer from the second gas to the sample droplets. In some implementations, the flow of second gas may be configured to create turbulence. The addition of the second gas results in increasing the ion signal provided to the mass analyzer, lowering chemical background in the ion signal, and decreasing contamination of the mass analyzer with non-analytical components.

[0022] Figure 3 is cross-sectional view of an example of an ESI device 300 according to an implementation of the present disclosure. The ESI device 300 includes a liquid sample conduit 304 and a coaxial first gas conduit 308 running through and extending from a surrounding support structure 312. The support structure 312 may be constructed from thermally and electrically insulating materials to minimize leakage of electrical current and heating of the liquid sample conduit 304. The sample conduit 304 provides a liquid sample flow path in a sample flow direction 316 along the axis of the sample conduit 304 to an open sample conduit tip 318. The first gas conduit 308 provides a first gas flow path of annular cross-section and co-directional with the sample flow. The first gas may serve as a nebulizing gas. The ESI device 300 produces an electrospray 320, or stream of electrically charged droplets, in the manner described above. The electrospray 320, while divergent to some degree, generally flows in the sample flow direction 316 collinear with the axis of the sample conduit 304. [0023] In the present example, the ESI device 300 includes an annular chamber 324 (e.g., a manifold, plenum, etc.) surrounding the liquid sample conduit 304 and the first gas conduit 308. A second gas supply conduit 328 is mounted at the support structure 312 in fluid communication with the annular chamber 324. The ESI device 300 also includes a housing 332 surrounding the liquid sample conduit 304 and the first gas conduit 308. The housing 332 includes a first end 334 attached to the support structure 312 in any suitable manner, and an opposing second end 336 located at an axial distance from the first end 334. The housing 332 may be cylindrical as in the illustrated example or may have any other suitable shape. The housing 332 may be constructed from a chemically inert material such as, for example, quartz. The ESI device 300 further includes a second gas conduit 340 located at a radial distance from the liquid sample conduit 304 and the first gas conduit 308. In the present context, "radial" refers to any direction orthogonal to the longitudinal axis of the sample conduit 304. The second gas conduit 340 extends for some axial distance from the annular chamber 324 to the interior of the housing 332. The second gas conduit 340 includes a second gas conduit inlet 342 communicating with the annular chamber 324 and a second gas conduit outlet 344 communicating with the interior of the housing 332. An inner wall 348 of the housing 332 defines its interior and is located at a radial distance from the liquid sample conduit 304 and the first gas conduit 308. The housing interior extends for an axial distance from the second gas conduit outlet 344 to the second end 336 of the housing 332. The ESI device 300 thus provides a second gas flow path from the supply conduit 328, through the annular chamber 324, through the second gas conduit 340, through the housing 332, and out from the open second end 336 of the housing 332 and into the ionization chamber 106 (figure 1). It will be noted that the housing 332 is a component of the ESI device 300 and thus is physically distinct from the surrounding ionization chamber 106. Accordingly, the housing 332 is disposed within the ionization chamber 106.

[0024] In some implementations such as illustrated in figure 3, the second gas conduit 340 may be located between a portion of the support structure 312 and a portion of the housing 332. The second gas conduit 340 may be a physically distinct structure such as a tube or a chamber, or may be a channel formed in the support structure 312 and/or the housing 332. In the illustrated example, the second gas conduit 340 is formed between a flat surface of the housing 332 and a groove, depression or recess formed in a portion of the support structure 312. The second gas conduit 340 and its outlet 344 may have any configuration suitable for providing a second gas flow path 352 into the housing 332 that runs in the sample flow direction 316 (and the direction of the charged droplet stream 320) and surrounds the sample conduit 304 while being constrained by the inner wall 348 of the housing 332. In the example specifically illustrated in figure 3, the second gas conduit 340 is helical (or spiral), and thus the flow path of the second gas through this conduit 340 is likewise helical. Hence, the second gas conduit 340 (and the resulting flow path therethrough) runs along the axial direction at a radial distance from a central axis (the sample conduit axis in the present example) while turning about the central axis, at a desired helical pitch and for a desired number of turns. The second gas conduit 340 is fashioned in the illustrated example by forming a helical groove in a surface of the support structure 312. The second gas conduit outlet 344 is located and oriented so as to continue the helical path provided by the second gas conduit 344. Hence, the second gas enters the housing interior along a flow vector tangential to the sample flow axis, and travels along a helical flow path 352 toward the open second end 336 of the housing 332. The second gas conduit outlet 344 may be located at any desired radial distance between the sample conduit 304 and the inner wall 348 of the housing 332. In the illustrated example, the second gas conduit outlet 344 is located at (or near) the inner wall 348. Moreover, the second gas conduit outlet 344 may be located at any desired axial distance from the sample conduit tip 318 as necessary for developing the helical gas flow 352 in the housing 332 that eventually interacts with the electrospray 320.

[0025] In the presently described implementation, the flow 352 of second gas from the second gas conduit 340 into the housing 332 may be considered as being a vortex or cyclone flow. From the perspective of any transverse plane through the housing 332 (perpendicular to the sample conduit axis), the helical flow path 352 (or at least its cross-section in the transverse plane) may be considered as being circular or annular. Yet the helical flow path 352 runs in the same resultant direction 316 as the liquid sample flow path and the flow path of the electrospray 320, in that all of these flow paths run generally from the ESI device 300 toward the ionization region outside the open second end 336 of the housing 332 of the ESI device 300. The inner wall 348 of the housing 332 reduces the dispersion of the second gas flow path 352 away from the ionization region, and also reduces the diffusion of the ion beam (being formed from the electrospray 320), and thus increases the ion signal intensity.

[0026] The second gas flow path 352 runs along the axial direction at a radial distance from a central axis (second gas axis) while, in the case of the illustrated helical flow, also turning about the central axis. Whether or not the second gas flow path 352 is helical, the flow path 352 is geometrically or mathematically defined relative to this central axis. In the example illustrated in figure 3, the second gas flow path 352 is generally symmetrical about the sample conduit axis (corresponding to the sample flow direction 316), and thus the axis of the second gas flow path 352 may be considered as being the same (or collinear with) the sample conduit axis. Alternatively, the second gas flow path 352 may be parallel to, but offset at a radial distance from, the sample conduit axis. In another alternative, the axis of the second gas flow path 352 and the sample conduit axis are not parallel, which for example may be accomplished by appropriately modifying the second gas conduit exit 344 or the inner wall 348 of the housing 332. [0027] In some implementations as shown in figure 3, the sample conduit tip 318 may be located entirely within the housing 332. That is, the axial distance of the sample conduit tip 318 from some reference plane 356, for example at the axial position of the second gas conduit outlet 344, may be less than the axial distance of the second end 336 of the housing 332 from the same reference plane 356. Alternatively, the sample conduit 304 may extend beyond the second end 336, i.e., the axial distance of the sample conduit tip 318 from the reference plane 356 may be greater than the axial distance of the second end 336 of the housing 332 from the reference plane 356. As a further alternative, the respective axial positions of the sample conduit tip 318 and the second end 336 may be the same. These variations are illustrated in figure 3 by a plane 358 corresponding to the axial position of the sample conduit tip 318 and arrow 360 corresponding to the axial position of the second end 336 relative to that of the sample conduit tip 318. By way of example, the relative position of the second end 336 of the housing 332 to the plane 358 of the sample conduit tip 318 may range from -50 mm to +100 mm. In other words, the second end 336 may be positioned anywhere from 50 mm short of the sample conduit tip 318 (in which case the sample conduit tip 318 is outside the housing 332) to 100 mm beyond the sample conduit tip 318 (in which case the sample conduit tip 318 is inside the housing 332). In another example, the second end 336 is located relative to the sample conduit tip 318 in the range from -20 mm to +50 mm. In another example, the range is from -10 mm to +25 mm. In yet another example, the range is from -5 mm to +15 mm. The range from -5 mm to +15 mm is expected to be preferred in many applications, although it will be understood that none of these ranges is intended to limit the broad teachings of the present disclosure. [0028] As noted above, the second gas stream may be heated. For many applications, the second gas stream preferably is heated to provide a desired amount and rate of heat transfer to the electrospray 320. In the example illustrated in figure 3, a heater 364 (or heating element) is positioned in thermal communication with the second gas supply conduit 328 at some point upstream of the internal chamber 324 and the internal second gas conduit 340 that feeds the housing 332. Any suitable type of heater 364 may be provided. Figure 3 also shows an alternative in which a heater 366 is provided in or integrated with the support structure 312 at a location adjacent to the second gas conduit 340. As a further alternative, a heater (not shown) may be located directly in the second gas conduit 340.

[0029] Figure 4 is cross-sectional view of another example of an ESI device 400 according to an implementation of the present disclosure. The ESI device 400 in this example includes a heater 468 located directly in the second gas conduit 340. As an example, the heater 468 may be a resistive wire formed from any suitable electrically conductive yet sufficiently resistive material. In implementations where the second gas conduit 340 is helical, the heater wire may likewise be helical as shown in figure 4. [0030] Figure 5 is cross-sectional view of another example of an ESI device 500 according to an implementation of the present disclosure. In this example, the second gas flow path 352 has a central axis 570 that is parallel with, but offset by a radial distance from, the sample conduit axis 516. In the illustrated example, the parallel but offset relation is accomplished by offsetting the position of the sample conduit 304 relative to the interior of the housing 332, but flowing the second gas symmetrically relative to the axis of the housing 332 as in the case of figures 3 and 4. [0031] Figure 6 is cross-sectional view of another example of an ESI device 600 according to an implementation of the present disclosure. In this example, a second gas conduit 640 is provided in the form of a plurality of passages 672 formed through the wall of the housing 332 and axially spaced from each other along the length of the housing 332. The passages 672 may all communicate with an upstream gas supply manifold (not shown) located outside the housing 332. The passages 672 may be oriented so as to introduce the second gas tangentially into the housing 332. The resulting helical or vortex gas flow path 352 may be similar to that described above in conjunction with figures 3-5.

[0032] Figure 7 is cross-sectional view of another example of an ESI device 700 according to an implementation of the present disclosure. In this example, a non-helical second gas conduit 740 is provided. As in the above-described implementations, the second gas conduit 740 is located at a radial distance from the liquid sample conduit 304 and the first gas conduit 308 and extends for some axial distance from the annular chamber 324 to the interior of the housing 332. The second gas conduit 740 also includes a second gas conduit inlet 742 communicating with the annular chamber 324 and a second gas conduit outlet 744 communicating with the interior of the housing 332. As in other implementations, the second gas conduit 740 may be located between a portion of the support structure 312 and a portion of the housing 332, and may be a physically distinct structure or formed entirely or partially by a feature of the support structure 312 and/or the housing 332. Unlike the above-described implementations, however, in figure 7 the second gas conduit 740 is provided in the form of an annular gap (or cylinder) coaxially surrounding the liquid sample conduit 304 and the first gas conduit 308. The annular gap may, for example, be formed between a portion of the support structure 312 and a portion of the housing 332 (or between two portions of the support structure 312). Like in the above-described implementations, the second gas conduit 740 and its outlet 744 are configured for providing a second gas flow path 752 into the housing 332 that runs in the sample flow direction 316 and surrounds the sample conduit 304 while being constrained by the inner wall 348 of the housing 332. In the present example, the resulting second gas flow path 752 into the housing 332 is annular or cylindrical about the liquid sample conduit 304 and the first gas conduit 308. That is, the second gas conduit 740 (and the resulting flow path) runs along the axial direction at a radial distance from a central axis (the sample conduit axis in the present example), but without turning about the central axis as in the above-described helical cases. [0033] The flow 752 of second gas from the second gas conduit 740 into the housing 332 may be considered as being an annular or cylindrical flow. Like in the case of the helical flow path 352 shown in figures 4-6, from the perspective of any transverse plane through the housing 332 the second gas flow 752 (or at least its cross-section) path illustrated in figure 7 may be considered as being circular or annular and as running in the same resultant direction 316 as the liquid sample flow path and the flow path of the electrospray. In other words, in either the case of the helical flow path 352 and the annular flow path 752, the second gas flow includes an annular component surrounding the sample conduit 304. The inner wall 348 of the housing 332 again reduces the dispersion of the second gas flow path 752 away from the ionization region, and also reduces the diffusion of the ion beam and thus increases the ion signal intensity. The second gas flow path 752 runs along the axial direction at a radial distance from a central axis. In the example illustrated in figure 7, the second gas flow path 752 is generally symmetrical about the sample conduit axis, and thus the axis of the second gas flow path 752 may be considered as being the same (or collinear with) the sample conduit axis. Alternatively, the second gas flow path 752 may be parallel to, but offset at a radial distance from, the sample conduit axis, as for example in the case of figure 5. In another alternative, the axis of the second gas flow path 752 and the sample conduit axis are not parallel. As an example, the second gas conduit outlet 744 or the inner wall 348 of the housing 332 may be configured to cause flow directions of at least part of the second gas flow path 752 to not be parallel with the sample flow direction 316.

[0034] In the implementation illustrated in figure 7, the axial location of the sample conduit tip 318 relative to that of the second end 336 of the housing 332 may be positioned before, at, or beyond the second end 336 as described above. As also described above, the second gas stream may be heated by a heating element provided at any desired location internal or external to the ESI device 700.

[0035] In other implementations, the helical second gas conduit 340 of figure 3, 4 or 5 or the annular second gas conduit 740 of figure 7 may be provided as a plurality of individual conduits that include respective inlets communicating with the annular chamber 324 and outlets communicating with the housing 332. In the case of helical second gas conduits 340, these may resemble a multi-start thread. In the case of non-helical second gas conduits 740, these may be provided as a plurality of circumferentially spaced through-bores or channels instead of a single, contiguous annular gap. [0036] Figure 8 is cross-sectional view of another example of an ESI device 800 according to an implementation of the present disclosure. As in other implementations, the ESI device 800 includes a housing 832 of sufficient axial length for bounding a helical or non-helical second gas flow path (not shown). In the present implementation, the housing 832 includes a tapered section 776. In the implementations described in conjunction with figures 3-7, at least that portion of the housing 832 defining the interior surrounding the sample conduit 304 has a constant inside diameter — for example, the inside diameter may be constant over the axial length from the second gas conduit outlet 344 to the second end 336 of the housing 732. However, in the implementation of figure 8, the inside diameter is reduced from a maximum value at the beginning of the tapered section 776 to a minimum value at the second end 336 of the housing 732. The cross-sectional flow area bounded by the tapered section 776 is consequently reduced. The second gas flow path through the housing 732 thus becomes more concentrated or focused toward the sample conduit axis as the second gas flows toward the sample conduit tip 318. This configuration may further facilitate the transfer of thermal energy from the second gas to the electrospray.

[0037] The presently disclosed ESI devices, including those illustrated in figures 3-8, may be utilized in any application entailing the conversion of a liquid sample into gas-phase ions. As an example, implementations taught in the present disclosure include an API interface that includes any of the presently disclosed ESI devices, and an MS system that includes any of the presently disclosed ESI devices. API interfaces and associated MS systems have been generally described in the present disclosure, including one example of an API interface 102 illustrated in figure 1. Other details of various types of API interfaces and MS systems are known to persons skilled in the art and thus need not be described further herein. The presently disclosed ESI devices may be utilized with or without a separate flow of drying gas 124 being introduced in the vicinity of the sampling orifice 122 shown in figure 1.

[0038] In general, terms such as "communicate" and "in . . . communication with" (for example, a first component "communicates with" or "is in communication with" a second component) are used herein to indicate a structural, functional, mechanical, electrical, signal, optical, magnetic, electromagnetic, ionic or fluidic relationship between two or more components or elements. As such, the fact that one component is said to communicate with a second component is not intended to exclude the possibility that additional components may be present between, and/or operatively associated or engaged with, the first and second components. [0039] It will be understood that various aspects or details of the invention may be changed without departing from the scope of the invention. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation — the invention being defined by the claims.

Claims

WHAT IS CLAIMED IS:

1. An electrospray ionization device comprising: a sample conduit comprising a sample conduit tip and providing a liquid sample flow path in a sample flow direction; a first gas conduit surrounding the sample conduit and comprising an annular first gas outlet, the first gas conduit providing a first gas flow path in the sample flow direction; a support structure surrounding the sample conduit; a housing surrounding the sample conduit and comprising a first end at the support structure and an axially opposite open second end; and a second gas conduit comprising a second gas inlet and a second gas outlet in open communication with the housing, wherein the second gas conduit is configured to provide a second gas flow path from the second gas outlet into the housing that is in the sample flow direction, surrounds the sample conduit and is constrained in a radial direction by the housing.

2. The electrospray ionization device of claim 1, wherein the second gas conduit is helical and the second gas flow path provided by the second gas conduit is helical.

3. The electrospray ionization device of claim 1, wherein the second gas conduit is annular and the second gas flow path provided by the second gas conduit is cylindrical.

4. The electrospray ionization device of any of claims 1-3, comprising a heater located at a position selected from the group consisting of a position adjacent to the second gas conduit, a position in the second gas conduit, and a position at a gas supply conduit upstream of the second gas conduit.

5. The electrospray ionization device of any of claims 1-4, wherein the housing comprises an inside surface and the second gas outlet is located at the inside surface.

6. The electrospray ionization device of any of claims 1-5, wherein the second end is located at an axial distance from the first end, and the axial distance of the second end is selected from the group consisting of the axial distance of the second end being less than an axial distance of the sample conduit tip from the first end, the axial distance of the second end being equal to the axial distance of the sample conduit tip from the first end, and the axial distance of the second end being greater than the axial distance of the sample conduit tip from the first end.

7. The electrospray ionization device of claim 6, wherein the axial distance of the second end relative to the axial distance of the sample conduit tip ranges from -50 mm to +100 mm.

8. The electrospray ionization device of any of claims 1-7, wherein the housing has an interior extending from the second gas outlet to the second end, and the interior has a diameter selected from the group consisting of a constant diameter, and a diameter less at the second end than at the second gas outlet.

9. The electrospray ionization device of any of claims 1-8, comprising a plurality of second gas conduits comprising a plurality of respective gas conduit inlets and gas conduit outlets.

10. The electrospray ionization device of any of claims 1-9, wherein the second gas flow path has a second gas flow axis, and the second gas flow axis has an orientation selected from the group consisting of collinear with the liquid sample flow path, parallel to and offset from the liquid sample flow path, and non-parallel to the liquid sample flow path.

11. The electrospray ionization device of any of claims 1-10, wherein the second gas flow conduit is interposed between the support structure and the housing.

12. The electrospray ionization device of claim 11, wherein at least a portion of the second gas flow conduit is bounded by a channel formed in the support structure or in the housing.

13. The electrospray ionization device of claim 1, wherein the second gas conduit is helical and the second gas flow path provided by the second gas conduit is helical, and further comprising a helical heater wire running though the second gas conduit.

14. The electrospray ionization device of any of claims 1-13, wherein the second gas conduit has a configuration selected from the group consisting of a configuration in which the second gas inlet is located at the support structure at an axial distance from the second gas outlet, and a configuration in which the second gas conduit comprises a plurality of passages through a wall of the housing.

15. A method for forming gas phase ions from a liquid sample, the method comprising: flowing the liquid sample through a sample conduit to a sample conduit tip; applying an electric field at the sample conduit tip in an ionization chamber surrounding the sample conduit tip, wherein the liquid sample flows from the sample conduit tip into the ionization chamber as a stream of electrically charged droplets; flowing a first gas around the sample conduit tip in the direction of the droplet stream to nebulize the droplets; and flowing a second gas in the direction of the droplet stream along a second gas path running between the sample conduit and a housing located in the ionization chamber and surrounding the sample conduit, wherein the second gas transfers heat to the droplets to promote evaporation of liquid and formation of gas phase ions.

16. The method of claim 15, wherein the second gas path is helical.

17. The method of claim 15, wherein the second gas path is annular.

18. The method of any of claims 15-17, comprising heating the second gas to a temperature ranging from room temperature to 600⁰C.

19. The method of any of claims 15-18, wherein the liquid sample is flowed along a sample flow axis and the second gas path flows relative to a second gas flow axis, and the second gas flow axis is selected from the group consisting of the second gas flow axis being collinear with the sample flow axis, the second gas flow axis being parallel to but offset from the sample flow axis, and the second gas flow axis being non-parallel with the sample flow axis.

20. The method of any of claims 15-19, wherein the second gas is flowed through a second gas conduit selected from the group consisting of a second gas conduit extending for an axial distance from a second gas inlet located at a support structure attached to the housing, and a second gas conduit comprising a plurality of passages through a wall of the housing.