US3057996A - Method and apparatus for operating an analytical mass spectrometer with a getter-ion pump - Google Patents

Method and apparatus for operating an analytical mass spectrometer with a getter-ion pump Download PDF

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Publication number
US3057996A
US3057996A US59901A US5990160A US3057996A US 3057996 A US3057996 A US 3057996A US 59901 A US59901 A US 59901A US 5990160 A US5990160 A US 5990160A US 3057996 A US3057996 A US 3057996A
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United States
Prior art keywords
pump
source
ion pump
valve
mass spectrometer
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Expired - Lifetime
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US59901A
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English (en)
Inventor
Ernest W Boyer
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ConocoPhillips Co
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Continental Oil Co
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Publication date
Priority to BE622048D priority Critical patent/BE622048A/xx
Application filed by Continental Oil Co filed Critical Continental Oil Co
Priority to US59901A priority patent/US3057996A/en
Priority to GB33354/61A priority patent/GB991902A/en
Priority to FR874785A priority patent/FR1305659A/fr
Application granted granted Critical
Publication of US3057996A publication Critical patent/US3057996A/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J41/00—Discharge tubes for measuring pressure of introduced gas or for detecting presence of gas; Discharge tubes for evacuation by diffusion of ions
    • H01J41/12—Discharge tubes for evacuating by diffusion of ions, e.g. ion pumps, getter ion pumps
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J49/00—Particle spectrometers or separator tubes
    • H01J49/02—Details
    • H01J49/24—Vacuum systems, e.g. maintaining desired pressures

Definitions

  • This application describes the method for connecting an ion pump with an analytical mass spectrometer.
  • a more detailed description of the novel hardware used to connect the ion pump tothe analytical mass spectrometer is contained in an application entitled Method and Apparatus for Connecting a Getter-Ion Pump to an Analytical Mass Spectrometer by ErnestW. Boyer, Harrell T. Ford, and Ernest E. McKelvey, filed concurrently with this application and assigned to the same assignee.
  • the diflusion pump Since the development of the analytical mass spectrometer the diflusion pump has been the source for obtaining the high vacuum required for its proper operation. While the diffusion pump has been more than adequate in obtaining a satisfactory vacuum for the proper performance of the spectrometer, the industry has been plagued with the length of time that the pump requires to obtain an adequate vacuum, especially with condensable light hydrocarbon. Maximum or minimum nitrogen levels in the cold traps fail to solvethe problem. Even when a programmed nitrogen level was used, the solution was far from satisfactory. The problem is further compounded by a compound such as ethane which is condensed to a volatile liquid under trap conditions and is in equilibrium with cold trap and source region. Under these conditions, it causes a variable background which cannot be eliminated by simply subtracting the background as measured before recording a sample spectrum.
  • a compound such as ethane which is condensed to a volatile liquid under trap conditions and is in equilibrium with cold trap and source region. Under these conditions, it causes a variable background which cannot be eliminated by simply subtracting the background
  • the ion pump permits the elimination of the troublesome cold trap and thus permits direct coupling between the ion pump and source.
  • the application of an ion pump to a mass spectrometer is not new; however, the use was limited solely to a spectrometer which was analyzing simple systems. Since the ion pump is species selective, thatis, will pump one entity faster than another, it was determined to be impossible to apply the pump to an analytical mass spectrometer that obviously requires the pumping of widely different compounds. The molecules having differentsizes and atomic structures would be operated on bythe eleetronicstream of the pump differently. The pumping rate would, of course, be determined by notonly the molecular size, that is, how large an area the molecule presented.
  • the ion pump creates new problems since it is species selective in its pumping rate. Thus, the ion pump will pump various entities at a different rate, thereby upsetting the ratio of the entities at the sourceand resulting in errors in the analysis of the mixtures under test.
  • the ion pump has a further difficulty in that. if the entire system requires venting for any reason, such as maintenance on the source, the system must be opened to the atmosphere. When the system is again evacuated, the ion pump, is roughed to approximately 20 microns; when this pressure is reached, .the power supply to the ion pump is energized. The nature of the pump is such that at operation at these pressures (about microns), the pump heats up.
  • Entities as used in this specification, shall mean any particles or combination of particles (molecules, atoms, etc.) in a charged or uncharged state.
  • an object of this invention todisclose a method for connecting an ion pump to an analytical mass spectrometer in a manner that will eliminate the species selectiveness of the ion pump.
  • This invention primarily features an analytical mass spectrometer which has .a source geometry which controls the conductance of the system sufficientlyso that the ion pump will not operate upon the source in a species selective manner.
  • the source conductance is controlled by increasing the resistance to the flow of gases from the leak to the pump by inserting bafiles or other obstruction means near the..leak and. between the leak and the pump.
  • the bafiles are preferably mounted in the source.
  • FIG. 1 is apartial sectional drawing of-the hardware used to couple the ion pump to the spectrometer source;
  • FIG. 2 is a graph showing the improvement of the exhaust ratefor a condensable lighthydrocarbonj
  • FIG. 3 is a graph showing the comparison inthe species selectivity between the differential pump .andthe 'io'n pump for two radically different molecules; i
  • FIG. 4 is a graphshowing the improvement in the exhaust rate of the ion pump underthe diffusion-pump using radically different hydrocarbon as best sampled.
  • FIG. 5 illustrates other diaphragms used to restrict flow of entities.
  • an ion pump 10 is shown con nected' to an analytical mass spectrometer sourcefll through air-tight hardware which comprises a cylindrical tube 12 which has a flange 13 adapted to mate with an output flange 14 of the ion'pump. Flanges 13 and 14 are held together by any suitable means such as a plurality of bolts 15.
  • a high vacuum valve 16 is connected to the end of cylindrical tube 12 opposite flange 13 by any suitable means such as shoulder'17.
  • High vacuum valve 16 may be any suitable valve capable of maintaining an air-tight seal during operation in either a closed or open position.
  • valve 16 The type of valve 16 used is coinmonly available and briefly incorporates a valve seat 18, a valve head 19 adapted to seal the end of cylinder 12 when the valve head and seat are mated.
  • a Itlireaded valve stem 20 passes through valve end 21 and has one end rotatably attached to valve head 19v and the other end rigidly attached to a suitable handle or nob 2i.
  • a bellows 23 is sealably attached to the top of the valve and,to the periphery of the valve head.
  • valve 16 The output 24 of valve 16 isconnected to a cylindrical portion 25.
  • Portion 25 includes a pair of pipes 26 and 27, respectively, attached to its periphery.
  • the first input 26 is connected to a vacuum gauge measuring means 28 and the second input 27 is connected to a valve 29.
  • the output of cylindrical portion is connected through a cylindrical portion 30 to spectrometer source 11.
  • cylindrical portion 30 is here shown to contain a labyrinth comprising a plurality of battles 31 supported within cylindrical portion 30 by any suitable means.
  • a second valve 32 Also connected to cylindrical portion 12 is a second valve 32 which is shown to be a valve similar to valve 16 and, therefore, will not be described.
  • valve 32 permits rapid evacuation of the chamber Within cylindrical tube 12; however, it is obvious that other types of valves may be used for either valve 32 or valve 16 providing they are sufiiciently air-tight during their operation in either the open or closed position.
  • a pipe 33 Connected to the outlet of valve 32 is a pipe 33 which is connected to the exhaust exit 34 of a mechanical pump 35.
  • a pipe 36 is connected between the outlet of valve 29 and exhaust exit 34 of mechanical pump 35.
  • a valve 37 is connected between pipe 36 and the air to permit venting of the spectrometer source in the event that Work must be done on the unit when the mechanical pump is connected.
  • Mechanical pump and pipe 36 may be disconnected by including a disconnect 38 and 39, thereby freeing the pump for other uses in the laboratory.
  • Annular rings 42 and diaphragm 43 are rigidly attached within cylindrical tube 12 and aid in the elimination of secondary emission entities.
  • valve 16 With valve 16 in an open position ion pump 10 evacuates cylindrical tube 12, cylinder portions 25 and 30, and spectrometer source 11; both valves 32 and 29 under normal operation are operated in a closed position thereby preventing the entry of air into the evacuated system.
  • a plurality of bafiles or diaphragms 31 Inserted within tube portion 30 is shown a plurality of bafiles or diaphragms 31. These bafiles show one method of increasing the source conductance so that the pump can not pump each species in the analytical spectrometer source at a different rate. Other methods of controlling the source conductance are possible, as for example, a plurality of right-angle bends.
  • FIG. 5 illustrates other forms of restriction such as a slit or a plurality of holes 61 which may be used to impede the flow of gases from the leak to the pump 10.
  • the amount of resistance imposed by the battles must exceed a minimum amount which is sufiicient to prevent the pump from operating on the entities in the system relatively, and by a maximum amount determined by the pressure of the source.
  • the minimum resistance can be determined by placing, under test, two dilterent compositions such as methane and butane or hydrogen and helium, in a predetermined blend and scanning the source composition over a period of time. A decrease in the ratio of the compound from the original mixture would indicate that the resistance was too low and that additional resistance was required.
  • the method for determining if an excess resistance has been inserted in the line is to monitor a sensitive peak contributed to by more than one compound in a mixture and establishing that this peak does not increase with increased time of flow through the leak. In actual practice it is best to keep the resistance of the line to a level as near the minimum as possible, since the greater the resistance the longer the pump-out time required.
  • valve 16 When for some reason the source must be shut down and the system vented, valve 16 is closed. This will permit continuous operation of pump 10, and will maintain cylindrical tube :12 in a highly evacuated state, thereby greatly reducing the time required to pump-down the system when the work on the source is completed. If mechanical pump 35 is connected in the manner shown in the drawing, that is, pipe 36 is connected to valve 29, valve 37 must be opened in order to let air into the system. Once the work is completed, valve 37 is closed and the mechanical pump energized.
  • Valve 16 while operating as a valve, also presents a unique feature not apparent.
  • the analytical mass spectrometer has been used to test samples of hydrocarbon and ion pump 10 has been used for a period of time
  • hydrocarbon molecules will become imbedded in the titanium surface on the inside of ion pump 10. If for some reason, as previously explained, the ion pump is disconnected or cylindrical tube 12 is filled with air, these molecules must then be evacuated when the pump is again re-energized.
  • the pump is initially started, the elevated temperatures which develop cause a release of entities previously pumped which may migrate up cylindrical tube 12 and back to source 11. This emission of migratory molecules if permitted to reach source 11 would obviously introduce errors during analysis.
  • cylindrical tube 12 may be bent at right angles and thereby result in the grounding or de fleeting of the charged or uncharged entities, the end result being, of course, to prevent the stray entities from migrating back to the spectrometer source and causing an interference in analysis,
  • annular ring 42 and diaphragm .43 are shown in cylindrical portion 12, they may be eliminated if valve 16 provides sufficient isolation for the sample under test. If valve 16 is eliminated, rings 42 and diaphragm 43 would be necessary to eliminate the secondary emission entities.
  • FIG. 4 illustrates the exhaust rate for .two radically different hydrocarbons.
  • the graph clearly illustrates that in both cases the ionpump with the modified source geometry exhausted the methane and butane at a much more rapid rate than did the diffusion pump and associated cold trap. Assuming that when a peak height of 5 divisions was reached that the analytical spectrometer was ready for use, a waiting period of less than lminute was all that was 'requiredto sufiiciently exhaustboth the methane and butane using the ion pump While a period of approximately 1% to 2 minutes was required for the diffusion pump.
  • Shownin the following chart is a plurality of compounds and their corresponding exhaust rate.
  • the ethane therefore would contrrbute to a variable back- In each case the most sensrtlve peak was selected in ground which could not be eliminated by simple subtraction of the background as measured before recording the sample spectrum.
  • FIG. 2 shows the problem of exhausting ethane with the usual diffusion pump. After a period of six minutes it can be seen that there were still at least divisions peak height of M/e28 remaining and 9 divisions peak height of M e30 remaining when a diffusion pump and cold trap were used. However, with the electronic or ion pump at the end of 6 minutes, a negligible number of divisions were read for both M/e28 and M e30 which indicated that sufficient ethane had been removed to give satisfactory operation with the ion pump. Since the usual time required to sufficiently evacuate the ethane was 30 minutes, a reduction from 30 minutes to 1 minute resulted in a substantial reduction in operating time.
  • FIG. 3 illustrates the complete lack of differential pumping when using the ion pump and the modified source.
  • Two radically difierent molecules were selected, namely, hydrogen and helium. The selection was for the purpose of determining whether the pumping rate would be different for molecules having radically different sizes and different charges.
  • a differential pumping effect would be evident by a change in slope between the plot of the hydrogen and helium molecules for either the diffusion pump or the electronic ion pump. Again using the peak height and a 50/50 mixture of the hydrogen and helium molecules, the graph clearly shows that the curves for the ion pump are substantially parallel order to provide more accurate information.
  • the first portion of the table tabulates the pump-out time for saturates, aromatics, cyclics, ketones, and alcohols which were selected as a representative sample of miscellaneous organic compounds to illustrate the times required to evacuate the system under normal analytical mass spectrometer temperatures of C.
  • the second portion of the table illustrates the pump-out time for a high temperature analytical mass spectrometer (350 C. inlet system). A plurality of heavy olefins, saturates, aromatics, and alcohols were selected. In the second portion of the chart it is obvious that a longer pump-out time is required; however, a portion of the extended time is a result of the fact that the mass spectrometer under use was sample side limited.
  • the method of exhausting the sample side was slower than the method of exhausting the source and thus a certain amount of pressure backed into the source side resulting in a longer pump-out time.
  • the limitations on the sample side were necessitated by the high temperature modifications.
  • an improvement on the high temperature pump-out system (valve sizes, etc.) of the analytical mass spectrometer would result in a much more rapid pump-out time for the heavy organic compounds.
  • an improvement comprising, interposing an obstruction in the proximity of said source whereby said source conductance is increased thereby rendering said pump non-species selective.
  • said obstruction comprises a plurality of diaphragms having openings therethrough whereby said gases are caused to change direction and velocity.
  • a device as described in claim 1 wherein said ohstruction comprises a diaphragm having a plurality of small openings therethrough.
  • An analytical mass spectrometer comprising in combination a source having an output, an ion pump having an output, means connecting the output of said ion pump to the output of said source, and obstruction means interposed within said connecting means between said pump and said source, said obstruction means adapted to control said source conductance.
  • An analytical mass spectrometer comprising in combination an analytical mass spectrometer source having an output, an ion pump having an output, and a pipe connected between said ion pump output and said spectrometer source output, said source additionally comprising means mounted therein which is adapted to control the conductance of said source by an amount sufficient to make said ion pump substantially non-species selective.
  • a mass spectrometer having a source, a selective pumping ion pump, and hardware connecting said pump to said spectrometer source, an improvement comprising, interposing an obstruction in the proximity of said source whereby said source conductance is controlled thereby rendering said pump non-species selective.

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  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Other Investigation Or Analysis Of Materials By Electrical Means (AREA)
US59901A 1960-10-03 1960-10-03 Method and apparatus for operating an analytical mass spectrometer with a getter-ion pump Expired - Lifetime US3057996A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
BE622048D BE622048A (US07714131-20100511-C00038.png) 1960-10-03
US59901A US3057996A (en) 1960-10-03 1960-10-03 Method and apparatus for operating an analytical mass spectrometer with a getter-ion pump
GB33354/61A GB991902A (en) 1960-10-03 1961-09-18 Method and apparatus for operating an analytical mass spectrometer with a getter-ion pump
FR874785A FR1305659A (fr) 1960-10-03 1961-10-02 Procédé et appareil pour le fonctionnement d'un spectromètre de masse analyseur en combinaison avec une pompe à ions

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US59901A US3057996A (en) 1960-10-03 1960-10-03 Method and apparatus for operating an analytical mass spectrometer with a getter-ion pump

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3761708A (en) * 1971-10-08 1973-09-25 Us Interior Electron suppressor grid for a mass spectrometer
US4195224A (en) * 1977-10-04 1980-03-25 Organisation Europeenne De Recherches Gas leakage detection apparatus
US4492110A (en) * 1983-06-01 1985-01-08 Martin Marietta Corporation Ultra sensitive noble gas leak detector
US4534204A (en) * 1983-06-01 1985-08-13 Martin Marietta Corporation Calibration method for ultra sensitive noble gas leak detector
US6498344B1 (en) * 1999-10-01 2002-12-24 Siemens Energy & Automation, Inc. Triode ion pump

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2769912A (en) * 1954-04-12 1956-11-06 Phillips Petroleum Co Shut-off valve
US2880323A (en) * 1955-06-03 1959-03-31 Phillips Petroleum Co Diffusion pump and mass spectrometer
US2967012A (en) * 1957-04-15 1961-01-03 High Voltage Engineering Corp Getter-ion pump

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2769912A (en) * 1954-04-12 1956-11-06 Phillips Petroleum Co Shut-off valve
US2880323A (en) * 1955-06-03 1959-03-31 Phillips Petroleum Co Diffusion pump and mass spectrometer
US2967012A (en) * 1957-04-15 1961-01-03 High Voltage Engineering Corp Getter-ion pump

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3761708A (en) * 1971-10-08 1973-09-25 Us Interior Electron suppressor grid for a mass spectrometer
US4195224A (en) * 1977-10-04 1980-03-25 Organisation Europeenne De Recherches Gas leakage detection apparatus
US4492110A (en) * 1983-06-01 1985-01-08 Martin Marietta Corporation Ultra sensitive noble gas leak detector
US4534204A (en) * 1983-06-01 1985-08-13 Martin Marietta Corporation Calibration method for ultra sensitive noble gas leak detector
US6498344B1 (en) * 1999-10-01 2002-12-24 Siemens Energy & Automation, Inc. Triode ion pump

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GB991902A (en) 1965-05-12
BE622048A (US07714131-20100511-C00038.png)

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