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US3342993A - Time-of-flight mass spectrometer having an accelerating tube with a continuous resistive coating - Google Patents

Time-of-flight mass spectrometer having an accelerating tube with a continuous resistive coating Download PDF

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Publication number
US3342993A
US3342993A US397814A US39781464A US3342993A US 3342993 A US3342993 A US 3342993A US 397814 A US397814 A US 397814A US 39781464 A US39781464 A US 39781464A US 3342993 A US3342993 A US 3342993A
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United States
Prior art keywords
field
region
ions
time
axis
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Expired - Lifetime
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US397814A
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English (en)
Inventor
Gerald J O'halloran
Lowell D Ferguson
Hayden M Smith
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Bendix Corp
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Bendix Corp
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Publication date
Application filed by Bendix Corp filed Critical Bendix Corp
Priority to US397814A priority Critical patent/US3342993A/en
Priority to DE19651598069 priority patent/DE1598069B1/de
Priority to GB39385/65A priority patent/GB1056957A/en
Application granted granted Critical
Publication of US3342993A publication Critical patent/US3342993A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J49/00—Particle spectrometers or separator tubes
    • H01J49/02—Details
    • H01J49/06—Electron- or ion-optical arrangements
    • H01J49/067—Ion lenses, apertures, skimmers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J49/00—Particle spectrometers or separator tubes
    • H01J49/26—Mass spectrometers or separator tubes
    • H01J49/34—Dynamic spectrometers
    • H01J49/40—Time-of-flight spectrometers

Definitions

  • the known type of time-offlight mass spectrometer comprises an ion source and a collector disposed at opposite ends of an evacuated fieldfree drift tube.
  • ions are formed, usually by electron bombardment, which are periodically pulsed out of the source by, source grids toward the collector by either one or .several electric fields established between appropriately spaced grids. Since the velocity of the ions in the field-free drift tube region is a function of the ratio of their charge q to their mass m, ion separation occurs corresponding to q/m, the amount of separation depending strongly on the length of the tube.
  • unit ionization source current is eifectively reduced. Reso-. lution is impaired because the field-free drift tube length is effectively shortened to insure that a sufiicient number.
  • ions may be transported from the ionization source region to the collector of a time-of-flight mass spectrometer with substantially greater efiiciency than heretofore attained.
  • spectrometer sensitivity is greatly enhanced.
  • the lens comprises an electric two-dimensional field region having a symmetry about an axis of rotation. It is formed by passing a current along the entire surface of a cylindrical envelope whose resistivity varies in a manner to produce a potential distribution upon its axis which is parabolic.
  • Such a lens as utilized to form the new timeof-fli'ght mass spectrometer, is a converging lens for positive ions, and is characterized by having a radial force component which is independent of axial or longitudinal position, and which is proportional to the radius or off axis position throughout the lens region.
  • the radial field, E is a central field which constrains the ions toward the central axis of the field while the axial field E accelerates the ions in the longitudinal axial direction.
  • ions in their transit through the lens region describe substantially simple harmonic motion about the central axis of the region as they are accelerated toward the collector.
  • the importance of the radial field is readily appreciated as it is this component which prevents the ions from striking the Walls of the lens region and becoming lost thereby.
  • the radial field is independent of longitudinal position and proportional to radius throughout the lens region, all ions of the same charge to mass ratio having the same axial velocity will arrive simultaneously at the collector.
  • an object of this invention to provide a new time-'of-fiight mass spectrometer in which the ion transport characteristic of known time-of-fiight mass spectrometers is improved.
  • FIGURE 1 is a sectional view comprising a time-offlight mass spectrometer in accordance with the invention
  • FIGURE 2 is an enlarged view of the electrostatic focusing field element of FIGURE 1;
  • FIGURE 3 illustrates the continuity of the axial parabolicpotential profile of the focusing field element shown in FIGURES 1 and 2;
  • FIGURE 4 illustrates the continuity of the axial potential gradient of the focusing field element of FIGURES l and 2.
  • envelope 9 in envelope 9 is shown an ion source region 10 positioned between a grounded backing plate 12 and an ion accelerating grid 14, which is spaced a distance S plus or minus a distance AS/2 from the aperture 16 of the grid.
  • Region 10 designates the region of ion formation typically accomplished by passing an electron beam 11 from a cathode 13 through a gas to be analyzed introduced into the region 10.
  • a power supply 15 is shown supplying a heater current which may be 2.5 to 3 amps to the cathode 13.
  • Cathode 13 has a negative potential bias supplied by source 15 to provide the ionizing electrons with energy sufficient to ionize the gas in region 10. This potential may include 1 to -l volts, depending on the gas to be ionized.
  • a tubular electrode lens element 20 of length L Disposed between grid 14 and ion collector 18 is a tubular electrode lens element 20 of length L which is cylindrically symmetric about the central axis 40 and has.
  • Element 20 is characterized by having a continuous resistive surface 52 and is shown having two lead wires 26 and 28, one at each end of the element through which a constant potential V which may be 12Q0 volts, and V which may be -3600 volts applied from the power supply 30.
  • housing 34 Connected to the lenes element 20 is housing 34 which is of an electrically conductive material, for example stainless steel, shown having a length D. Housing 34 shares a common lead 28 with element 20 at one end of the housing and at the opposite end lead wire 32 is shown, both leads 28, 32 having the same potential V of -3600 volts from power supply 30.
  • a potential distribution having predetermined characteristics is thus produced along the resistive coating 52 of electrode 20 forming an electrostatic focusing field therein of specific lens focal properties. However, a field free region is formed within housing 34 since there is no potential drop across the length D' of the housing.
  • a voltage pulse U which may be 1200 volts
  • the heterogeneous group of ion masses formed in region are accelerated a distance S to aperture 16 of grid 14, each ion acquiring substantially the same kinetic energy but differing in exit velocity through aperture 16 in proportion to the square root of its charge to mass ratio, the heavier ions having lower velocities and therefore becoming separated from the lighter ions.
  • discrete ion bunches of different charge to mass ratios pass through aperture 16 and either drift or accelerate, depending on the specific U and V potentials through aperture 22 into the electrostatic focusing field of lens element 20.
  • the ions are subjected to a focusing field wherein a radial electric field component directs them toward the central axis 40 at the same time an axial electric field component accelerates them longitudinally along the central axis 40 toward the field terminating grid 24.
  • ions entering the focusing field region of element 20 are restrained from straying to the walls and becoming absorbed therein such that substantially all of the incoming ions are focused into a relatively narrow beam of spatially separated ion masses which exit through grid 24 and drift a length D, where mass separation is enhanced, to the collectorlS as'shown by the two typical trajectories 39 and 41. If only ions of the same charge are present,
  • the lightest group reaches the collector 18 first followed by groups of successively heavier mass.
  • the performance of the new mass spectrometer may be illustrated with reference to its resolving power.
  • a convenient measure of resolution is the largest mass m, for which adjacent masses are essentially completely separated. If all the ions formed in region 10 were formed at an infinitesimal point spaced from the accelerating grid 14 with the same initial velocity vector, the flight time from the source to the collector 18 would be the same for all ions having the same charge to mass ratio, and the spectrometer resolution would be limited only by the detecting apparatus 42.
  • the over-all resolving power of the spectrometer depends on its ability to reduce ion flight time spread through the instrument caused by the ever present initial space and initial kinetic energy distributions.
  • space resolution refers to ions formed at different distances about the S distance and is shown in FIGURE 1 occurring in a deviation of AS/ 2.
  • Energy resolution refers to ions formed within region 10 having velocity vectors both parallel and non-parallel to the spectrometer axis 40 immediately before the time they are pulsed out of region 10.
  • the overall resolution of the spectrometer is determined by the respective space and energy resolutions which are in turn complex functions of the pulsed potential U,,; the ratio of the potentials V /V and VO/UO; nd the distance parameteres S d, L and D.
  • the spectrometer space and energy resolution capabilities are respectively 650 and 443 atomic mass units for ions formed at room temperature.
  • FIGURE 2 an enlarged view of the lens element 20 of FIGURE 1 is shown.
  • the orientation of the electric field is illustrated 'by' the coordinate axes r', z,
  • the specific focusing field for-med within lens element 20 is one characterized by being rotationally symmetric about the axis 40 and having anaxial potential distribution along its length which is parabolic as shown in FIGURE 3.
  • Rotationally' symmetric means that any point a distance r fromthe longitudinal axis 40 and in a plane transverse to the axis 40 has exactly the same field vector as every other point in that'plane a'distance r from the axis 40.
  • the resistance per unit length p of material 52 must continuously increase along the length of the lens element 20 from aperture 22 to grid 24 so that the potential gradient dV/dz (the potential drop per unit length), increases along the resistive material 52 in proportion to the axial displacement from aperture 22' as hereinafter explained in connection with FIGURE 4.
  • One method which may be used to obtain a continuously increasing resistance is shown in FIG- URE 2 where material 52 is gradually decreasing in thickness in an axial direction from aperture 22 to grid 24 and satisfies the equation where K is a constant.
  • the conical conductive surface 58 of electrode 54 preserves the field geometry at the ion entrance aperture 22 of FIGURE 2 because it forms an angle a of 54 44 with axis 40 which is also the asymptotic equipotential boundary of the hyperboloidal equipotential surfaces 56.
  • Grid 24 at the opposite end of element 20 serves the purpose of providing an abrupt discontinuity of the field region.
  • FIGURE 3 as hereinbefore discussed, the axial potential distribution of the electric field formed within element 20 of FIGURE 2 is shown.
  • the important feature shown in FIGURE 3 is that the parabolic potential distribution is continuous along the entire axis of the field.
  • the highest point of the parabola corresponds to the entrance aperture plane 22 of FIGURE 2 and the lowest point corresponds to the exit grid plane 24.
  • FIGURE 4 The continuity of the electric field within element 20 of FIGURE 2 is further illustrated in FIGURE 4.
  • the potential gradient dV/ dz is shown increasing in an axial direction proportional to axial displacement and, as in FIGURE 3, represents the potential gradient along the axis of rotation 40 of the lens element 20 of FIGURE 2.
  • a mass spectrometer comprising an ion source
  • means for accelerating the ions from said source in a specified direction means for providing a rotationally symmetric field region having an entrance and exit means disposed to receive and discharge the accelerated ions,
  • said field region having an axial potential distribution in the form of a parabola with the highest value and lowest value of the parabola corresponding respectively with said field entrance and exit means.
  • said field region having a radial field which varies in proportion to the distance from the axis of the region but which is constant along the axis,
  • a mass spectrometer as set forth in claim 1 with said means for providing an electric field region comprising a continuous resistive electrode bounding said field region,
  • a mass spectrometer comprising an ion source
  • said field region having an axis disposed between said source and said collector means
  • said field region having an axially descending parabolic potential distribution with the highest value and the lowest value of the parabolic curve corresponding respectively with the source end of said region of acceleration on said axis and the collector end of said region of acceleration on said axis, whereby the accelerated ions are caused to converge as they approach the collector end of said region of acceleration,
  • said rotationally symmetric electric field having a radial field which varies in proportion to the distance from the axis of the acceleration region but which is uniform in the axial direction
  • said electric field providing a focusing action on ions entering said region of acceleration which ions after a single journey through said accelerating region are subsequently collected by said collector means

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Other Investigation Or Analysis Of Materials By Electrical Means (AREA)
  • Electron Tubes For Measurement (AREA)
US397814A 1964-09-21 1964-09-21 Time-of-flight mass spectrometer having an accelerating tube with a continuous resistive coating Expired - Lifetime US3342993A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
US397814A US3342993A (en) 1964-09-21 1964-09-21 Time-of-flight mass spectrometer having an accelerating tube with a continuous resistive coating
DE19651598069 DE1598069B1 (de) 1964-09-21 1965-08-21 Flugzeit-Massenspektrometer
GB39385/65A GB1056957A (en) 1964-09-21 1965-09-15 Mass spectrometer

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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3621242A (en) * 1969-12-31 1971-11-16 Bendix Corp Dynamic field time-of-flight mass spectrometer
US4714891A (en) * 1985-09-23 1987-12-22 Granville-Phillips Company Method and apparatus for improving the safety and extending the range of ionization gauge systems
US5097125A (en) * 1986-06-04 1992-03-17 Arch Development Corporation Photo ion spectrometer
EP1580548A1 (de) 2004-03-24 2005-09-28 Burle Technologies, Inc. Ionenmobilitätsspektrometer
WO2014194172A3 (en) * 2013-05-31 2015-02-26 Perkinelmer Health Sciences, Inc. Time of flight tubes and methods of using them
WO2015173616A1 (en) * 2014-05-12 2015-11-19 Shimadzu Corporation Mass analyser
US9355831B2 (en) 2013-06-03 2016-05-31 Perkinelmer Health Sciences, Inc. Ion guide or filters with selected gas conductance
US9355832B2 (en) 2013-05-30 2016-05-31 Perkinelmer Health Sciences, Inc. Reflectrons and methods of producing and using them
US9368334B2 (en) 2013-06-02 2016-06-14 Perkinelmer Health Sciences, Inc. Collision cells and methods of using them

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2739827A1 (de) * 1977-09-03 1979-03-15 Leybold Heraeus Gmbh & Co Kg Flugzeitrohr

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2570158A (en) * 1950-12-02 1951-10-02 Gen Electric Method and apparatus for separating charged particles of different mass-to-charge ratios
US2782316A (en) * 1952-06-20 1957-02-19 Cons Electrodynamics Corp Mass separation
US2971118A (en) * 1958-11-10 1961-02-07 Sylvania Electric Prod Electron discharge device
US3258591A (en) * 1961-12-22 1966-06-28 Pulse type mass spectrometer wherein ions are separated by oscillations in an electrostatic field

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE623769C (de) *
DE714010C (de) * 1935-03-19 1941-11-19 Telefunken Gmbh Elektrische Abbildungslinse aus mehreren auf verschiedenem Potential befindlichen Elektroden
GB534215A (en) * 1939-07-28 1941-03-03 Otto Klemperer Improvements in or relating to electron discharge devices
DE975107C (de) * 1953-05-15 1961-08-17 Telefunken Patent Elektrostatische Linse mit rotationssymmetrischen Elektroden, insbesondere fuer Kathodenstrahlroehren
DE1035282B (de) * 1955-09-07 1958-07-31 Dr Fritz Schneider Elektronen- bzw. ionenoptische Linsenanordnung

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2570158A (en) * 1950-12-02 1951-10-02 Gen Electric Method and apparatus for separating charged particles of different mass-to-charge ratios
US2782316A (en) * 1952-06-20 1957-02-19 Cons Electrodynamics Corp Mass separation
US2971118A (en) * 1958-11-10 1961-02-07 Sylvania Electric Prod Electron discharge device
US3258591A (en) * 1961-12-22 1966-06-28 Pulse type mass spectrometer wherein ions are separated by oscillations in an electrostatic field

Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3621242A (en) * 1969-12-31 1971-11-16 Bendix Corp Dynamic field time-of-flight mass spectrometer
US4714891A (en) * 1985-09-23 1987-12-22 Granville-Phillips Company Method and apparatus for improving the safety and extending the range of ionization gauge systems
US5097125A (en) * 1986-06-04 1992-03-17 Arch Development Corporation Photo ion spectrometer
EP1580548A1 (de) 2004-03-24 2005-09-28 Burle Technologies, Inc. Ionenmobilitätsspektrometer
US9859106B2 (en) 2013-05-30 2018-01-02 Perkinelmer Health Sciences, Inc. Reflectrons and methods of producing and using them
US9355832B2 (en) 2013-05-30 2016-05-31 Perkinelmer Health Sciences, Inc. Reflectrons and methods of producing and using them
US9384954B2 (en) 2013-05-31 2016-07-05 Perkinelmer Health Sciences, Inc. Time of flight tubes and methods of using them
WO2014194172A3 (en) * 2013-05-31 2015-02-26 Perkinelmer Health Sciences, Inc. Time of flight tubes and methods of using them
US9899202B2 (en) 2013-05-31 2018-02-20 Perkinelmer Health Sciences, Inc. Time of flight tubes and methods of using them
US9368334B2 (en) 2013-06-02 2016-06-14 Perkinelmer Health Sciences, Inc. Collision cells and methods of using them
US10103013B2 (en) 2013-06-02 2018-10-16 Perkinelmer Health Sciences, Inc. Collision cells and methods of using them
US9818592B2 (en) 2013-06-03 2017-11-14 Perkinelmer Health Sciences, Inc. Ion guide or filters with selected gas conductance
US9355831B2 (en) 2013-06-03 2016-05-31 Perkinelmer Health Sciences, Inc. Ion guide or filters with selected gas conductance
US20170084445A1 (en) * 2014-05-12 2017-03-23 Shimadzu Corporation Mass analyser
US9786485B2 (en) * 2014-05-12 2017-10-10 Shimadzu Corporation Mass analyser
WO2015173616A1 (en) * 2014-05-12 2015-11-19 Shimadzu Corporation Mass analyser

Also Published As

Publication number Publication date
GB1056957A (en) 1967-02-01
DE1598069B1 (de) 1970-09-24

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