US 3886357 A
A multiple ion beam type double focusing mass spectrometer designed to control ion beams from a plurality of ion sources so as to form a single beam. The single ion beam is introduced into an electric field while the accelerating voltages or electric field intensity is varied stepwise so that by means of the energy dispersion effect of said electric field, the respective ion beams accelerated at different accelerating voltages are repeatedly and sequentially introduced into a magnetic field. At the output side of the magnetic detector, an ion detector detects said repeatedly and sequentially introduced ion beams and converts them into time shared signals.
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Description (OCR text may contain errors)
United States Patent Naito 1 May 27, 1975  MULTIPLE [ON BEAM TYPE DOUBLE 3,689,764 9/1972 Green et al. 250/296 F C S MASS SPECTROMETER 3,796,872 3/1974 Merren 250/285 [75} Inventor: Motohiro Naito, Akishima, Japan Primary Examiner james Lawrence  Assignee: Nihon Denshi Kabushiki Kaisha, Assistant Examiner-B. C. Anderson Tokyo, Japan Attorney, Agent, or FirmWebb, Burden, Robinson 8L  Filed: Dec. 18, 1973 Webb 1 1 pp 425,923 [57 ABSTRACT A multiple ion beam type double focusing mass spec-  Foreign Application Priority Data trometer designed to control ion beams from a plural- Dec. 18, 1972 Japan 47-12694? Juices as form a Single beam The gle ion beam is introduced into an electric field while  CL 5 250/283; 250/296 the accelerating voltages or electric field intensity is 511 1m. (1. n01 j 391/34 varied Stepwise so that by means of the energy disper-  Field of Search U 33 285, 295 296, sion effect of said electric field, the respective ion 250/297, 299 beams accelerated at different accelerating voltages are repeatedly and sequentially introduced into a mag-  References Cited netic field. At the output side of the magnetic detec- UNITED STATES PATENTS tor, an ion detector detects said repeatedly and se- 2 45 7,1960 B b k t l 50/296 quentially introduced ion beams and converts them ru a ere a 3,233,099 2/1966 Berry er al 250/296 mm mm Shared Slgnals' 3,475.604 10/1969 Noda et a1. 250/295 10 Claims, 5 Drawing Figures ncrazxnrme v 9 VOL T465 .7
PM/ER SOURCE 8 516N741, I
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\ 1 25 Gin/ERA ml! 23 10 1M Mum sol/kc: .s'ouRcz .3001? c: i sue/v41.
[ji T- a PROCEJJ'OR l u 11 3 i r l canRrcr/we M I P0: AMPLIFIER 22 l Gin Emma I 1 PATENTED MAY 2 7 ms SHEET (Sec) 6 king l MULTIPLE ION BEAM TYPE DOUBLE FOCUSING MASS SPECTROMETER BACKGROUND OF THE INVENTION This invention relates to a mass spectrometer and more particularly to a multiple ion beam double focusing mass spectrometer for analyzing a plurality of ion beams in a single mass spectrometer unit so as to obtain time shared signals.
Conventional multiple ion beam type mass spectrometers are usually provided with deflection plates for forming periodic ion beams. The periodic ion beams are directed to the mass spectrometer proper and detected as time shared multiple signals. Finally, the multiple signals are separated by a signal processing device to obtain a plurality of mass spectra.
With such an apparatus, since the ion beams emitted by the ion source are required to be either completely on or off, deflection pulses having very high potentials must be applied to achieve sufficient deflection. These deflection pulses, since they subject the ion beams to high energy dispersion, impair the resolution of the mass spectrometer considerably. Also, as the energy range of the ions passing through the normally very narrow indicent slit of the apparatus is limited, the flow rate of the ion beams directed through the mass spectrometer is consequently decreased and this again lowers the sensitivity of the apparatus. There is also a difference in the degree of deflection of the ion beam emitted from the respective ion sources. As a result, the dispersion, aberration and intensity of the individual ion beams emitted from the ion sources differ from each other which adversely affects the analyzing precision of the apparatus. The resolution is further impaired as the ion beams processed and already proceeding in particular directions are subjected to unfavorable deflection owing to the effects of the rise and fall time of the deflection pulses which produce transient variations in the electric field. Even ifa deflection is produced in the longitudinal direction of the slit, assuming that a troidal electric field is being applied, a negative effect on the resolution would be virtually unavoidable.
SUMMARY OF THE INVENTION The purpose of this invention is to provide an innovative multiple ion beam type double focusing mass spectrometer for analyzing a plurality of ion beams using only a single instrument while at the same time being able to obtain time shared or spliced multiple signals.
Briefly, according to this invention, ion beams from separate ion beam sources are directed along a common line to the electrostatic analyzer of a double focusing mass spectrometer. Each ion source is provided with an accelerating field controlled by an accelerating voltage source. Ion beam pulses from at least one of the plurality of beams are intermittently passed from the electrostatic analyzer to the magnetic analyzer because the power supply for the accelerating voltage of that ion source and/or the power supply for the electrostatic analyzer are controlled to vary the ratio of the accelerating voltage and the electric field of the electrostatic analyzer such that the ions from that ion source have the range of energies to pass through the electrostatic analyzer and the slit in the baffle following the electrostatic analyzer only during spaced periodic intervals.
According to one embodiment, ion beam pulses from each of the plurality of ion beam sources are sequentially passed to the magnetic analyzer ad seriatim. In this embodiment, the ratio of accelerating voltage for each ion source and the electrostatic field of the electrostatic analyzer are adjusted such that only the ions from one source at a time have the range of energies enabling them to pass through the electrostatic analyzer and the slit in the baffle following the electrostatic analyzer.
In another embodiment of this invention, the respective accelerating voltages supplied to a plurality of ion sources are sequentially varied so that each accelerating voltage is periodically returned to a reference level for a given pulse duration. The ion beams emitted from the ion sources are accelerated according to the accelerating voltage aligned along a common path, to pass through the entry slit of the electrostatic analyzer. The intensity of the electric field of the electrostatic analyzer is fixed at a level whereby only beams accelerated by the reference accelerating voltage can travel the common path and in repeated sequence, be guided into the focusing magnetic field of the magnetic analyzer. The ion beams are detected and amplified by an electron multiplier. They provide a time shared or spliced multiple signal in the detector corresponding to the beam passed through the electrostatic analyzer. The electric field of the electrostatic analyzer has a further purpose to correct ion energy aberrations for any of the individual ion beams. In a specific embodiment of this invention, an apparatus is designed so that the ion beams emitted from a plurality of ion sources are each accelerated by voltages of differing values and directed into a common path. The ion beams in this case, are guided into the electric field of the electrostatic analyzer which corrects the energy aberrations of the ions. The intensity of the electric field is varied in a repeated sequence so that only one ion beam accelerated by its particular accelerating voltage is directed into the focusing magnetic field at one time. As a result, time shared multiple signals are detected in the detector.
In yet another embodiment of this invention an apparatus is designed to fix any one of the accelerating volt ages supplied to the plurality of ion sources at a reference level and vary the remaining voltage or voltage impulses selecting the pulse width and phase to produce a repeated sequence wherein the varied accelerating voltages are at the reference level. Simultaneously, the intensity of the electric field is accurately fixed at a level corresponding to the reference accelerating voltage that passes into the magnetic analyzer. The ion beam from the ion source to which the fixed accelerating voltage is supplied is continuously introduced into the focusing magnetic field and the ion beam or beams from the ion source to which the varied accelerating voltage is supplied are introduced into the focusing magnetic field either intermittently or in repeated sequence. Time shared multiple signals superimposed on the signals resulting from the ion beams accelerated by the fixed accelerating voltage are obtained in the detector.
A preferred feature applicable to an apparatus based on any of the previously described three embodiments includes a signal generator for initiating ion production and for determining the ion production period, repitition frequency and phase of the ion source. That is to say, in the apparatus where the accelerating voltage is varied. the ion producing period, repetition frequency and phase are determined so that the ion beams cannot be guided to the detector during the rise and fall time of the accelerating voltage. In the case where the intensity of the electric field of the electrostatic analyzer is varied, the ion producing period, repitition frequency and phase are determined by the generator so that the ion beams cannot be guided to the detector during the rise and fall time of the electric field intensity.
In all the above-described embodiments, an electron multiplying tube or Faraday cage may be employed as a detector. The magnetic field is swept to determine the mass to charge ratio of the ions being studied.
It is also possible to design a multiple ion beam mass spectrometer according to this invention, in which the magnetic field is locked and the accelerating voltage and electric field, which are mutually related, are swept. Since the accelerating voltage or the electric field is varied by pulses at set intervals, circuit construction becomes rather complicated. Should the apparatus be designed so that the sweeping signal and pulse are superimposed. however, the operation becomes far more practical.
For a better understanding of the advantages of this invention, reference should be made to the following detailed description based on the accompanying drawmgs.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a block diagram of one embodiment of the invention;
FIG. 2 shows a block diagram of another embodiment of the invention;
FIG. 3 shows waveforms for explaining the invention; and,
FIGS. 4 and 5 shows the waveforms obtained at the respective detector outputs according to the various embodiments of this invention.
DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, ion sources 1 and 2 generate ion beams which are aligned along a common path. Alignment of the beams is caused by deflection electrodes 3 and 4 to which a constant voltage is applied from power source 5. These deflection electrodes can be dispensed with if accurate superimposing of the ion beams is feasible by tilting the ion sources slightly relative to each other. A correcting electrode 6 eliminates high order aberration caused by a slight difference in incident angles of the ion beams emitted from the ion sources and is an essential component when high resolution mass spectra are required. The correcting electrode requires only a small square wave pulse for its effective operation. A control pulse generator 8 produces a square wave output which is applied to an accelerating voltage power source 9 and a correcting pulse generator 10. By superimposing mutually phase-reversed square waves from the control pulse generator 8 on the zero level voltage V produced by the accelerating voltage power source 9, accelerating voltages as shown in FIGS. 30 and b are applied to the ion sources 1 and 2. Since the accelerating voltage V,, is sufficiently larger than the amplitude A V of the square wave, the energy variation A E of the ion beams caused by A V becomes comparatively small. The correcting pulse from the correcting pulse generator 10 is synchronized with the control pulse from the control pulse generator 8 and the relative phases of the accelerating voltages are determined so that the ion beams corresponding to the period when the accelerating voltages are at V are properly corrected. The image at the collector side is focused on the main object slit in baffle 11. A second slit in baffle 12 limits the ion beam divergence angle and functions in the same way as the iris of an optical system. The electric field 13 of the double focusing mass spectrometer is basically provided to limit the energy aberration caused by ion beam dispersion and to obtain mass spectra of high resolution. It is designed in conjunction with the focusing magnetic field 14 so as to satisfy the more exacting requirements of the spectroscopes double focusing technique. In the double focusing technique, the parameters of the electrostatic analyzer and the magnetic analyzer are designed to focus ions having the same mass to charge ratio but somewhat different ini tial velocities and directions.
Ion beams emitted from the ion sources 1 and 2 are alternately accelerated by accelerating voltages V and V A V and superimposed so as to form a single ion beam which is introduced into the electric field 13 energized by a power source 15. The electric field 13 separates each ion beam accelerated by V, and A V V utilizing the dispersion effect. A third baffle having a slit for limiting the dispersion velocity of the ion beams is designed to allow only ions of a fixed energy range AE out of the total of ions dispersed throughout the electric field 13, to pass. Generally, each ion has a particular energy variation Ac when ionized. Since AE is larger than Ae by a sufficient amount, and the range of energy variations AE due to variations of the accelerating voltage AV is larger than the sum of AB and Ae, only ion beams which are accelerated when the accelerating voltage is V pass through the slit l6 and are guided towards the magnetic field l4. Said ion beams are then focused by said magnetic field 14 so as to impinge on the center of a terminal slit in baffle 18, thereby passing through to a detector 19 such as a Faraday cage where they are detected. The magnetic field 14 is swept by varying the voltage of the magnetic field power source 20 so as to make electrical detection possible of ions of different mass to charge ratios. The detected signal, which is a time shared multiple pulse having a square waveform, after being detected by the detector 19 and amplified by an amplifier 22, is passed to a signal processor 23. The detected signal whose amplitude and base line vary and which carries two items of information as shown by the solid line in FIG. 4, is synchronized and separated by a control pulse from the control pulse generator 8. Each mass spectrum is then coded and recorded for example in the memory of the signal processor 23.
Another embodiment of the invention will now be described referring still to FIG. I. The control pulse generator 8 supplies a control pulse having the same phase and waveform as the square wave shown in FIG. 3a to a signal generator 25 thereby initiating ion pro duction. Said signal generator supplies ion producing signals alternately during a period T to the ion sources 1 and 2. Ions are produced only during the period T, which is delayed relative to the rise and fall time of the control pulse by 6T and thus only occur within the period T/2 of the particular control pulse. Since no ions are produced at the rise and fall time of the accelerating voltages a and b, unfavorable deflection of the ion beams in the vicinity of the electric field 13, due to the transient accelerating voltage variations, is avoided. The processing of the ion beams is the same as described above.
FIG. 2 illustrates another embodiment of the invention. In the figure, the accelerating voltage power source 9 (the labelling in FIG. 2 corresponds with that in FIG. 1) applies accelerating voltages of differing levels to the ion beam sources 1 and 2, so that each ion beam source emits ions at different energy level. Each ion beam is deflected by the deflection electrodes 3 and 4 so as to converge them into a single beam which enters the electric field 13. The control pulse generator 8 supplies square wave control pulses to the electric field power source and the signal processor 23. By so doing, the electric field power source 15 supplies controlled voltages to the electrodes producing the electric field with the result that the field intensity, which is in synchonism with the energy of the ion beams emitted from the respective ion sources, is repeatedly and sequentially changed in accordance with the rise and fall time of said control pulses. The electric field 13 focuses the ions, corrects the aberration caused by the differences in the energy levels of the ions, and separates the multiple ion beams produced by the dispersion effect. The pulsed ion beams from the respective ion sources selectively pass through the dispersion limiting slit and are guided into the magnetic field 14 which is swept by the magnetic field power source 20. The magnetic field 14 also functions so as to focus the ion beams. The ion beams are then detected by the detector 19 and appear as the signal shown by the solid line in FIG. 4. This detected signal is separated in the signal processor in accordance with the control pulse from the control pulse generator 8 and recorded in the memory according to the mass spectrum of the particular ion beam.
In another embodiment of the invention, a control pulse from the control pulse generator 8 is applied to the signal generator 25 which controls ion production. Ions are produced only during the period T suitably delayed in relation to the rise and fall time of the control pulse by BT, and only occur within the period T/Z of the respective control pulse.
With the embodiment shown in FIG. 1, it is possible to create the accelerating voltage waveform supplied to each ion source independently in synchronization with the control pulse. In FIGS. 3a and b, the rise and fall times of the accelerating voltages coincide with each other. However, it is possible to design an apparatus in which said rise and fall times are timed so that as one accelerating voltage is rising, the other is falling with an appropriate delay and vice versa. In this case, although the multiple signal shown in FIG. 4 can be obtained in the detector, each plotted signal becomes a time shared pulse which returns to the base line.
It is also possible to design an apparatus in which one accelerating voltage is continually fixed at a specific value while the remaining accelerating voltages are varied. FIG. 5 shows the resultant detected signal obtained by such an apparatus. In this case, since one component of the signal is time shared and the other is the sum of both components, it is necessary to subtract the signal component from the added signal. Processing of the signal components is performed by the signal processor. If it is necessary to vary the flow rate of the ion beams from the individual ion sources, the desired effeet can be obtained by changing the time ratio during which the ion beams are guided to the magnetic field.
In a typical application of this invention, a standard sample such as parafluorokerosene is introduced at one ion source and the sample to be examined is introduced at the other ion source. Since the masscharge ratio of the standard sample is normally less than 800, regularly ordered spectra with a correctly known mass number can be obtained at every l2 to 14 mass numbers. If, however, the sample to be examined has a mass-charge ratio of more than 800, it will be impossible to verify the mass spectra by comparing said sample with a standard sample. In this case, the sample to be examined is introduced at the first ion source together with a standard sample, the combined samples are ionized and the resulting ion beams are accelerated by V At the same time, a standard sample only is introduced at the second ion source and is ionized and the resulting ion beams are accelerated by an accelerating voltage V larger in value than V Thus, the intensity of the elec tric field is converted alternately in accord with V and V at intervals sufficiently smaller than any one peak width. Superimposed spectra of both samples can be obtained in the detector where the mass spectrum from the second ion source appears in the position of greater mass. In this case, there is a correlation MN, M V between the mass numbers M and M which are accelerated by V, and V; respectively and arrive simultaneously at the collector. Now suppose V KV then the value for K can be obtained by comparing the known mass peak of the standard sample from the first ion source with the known mass peak of the standard sample from the second ion source so that the high mass peak of the sample being examined can be positively determined.
As described above, in this invention, it is possible to deal with multiple ion beams from a plurality of ion sources and channel them into a single ion beam. Further, it is possible to obtain mass spectra relevent to specific ion beams emitted from individual ion sources by using a single mass spectrometer making possible a wide range of applications such as the measurement of mass spectra of the same sample with different source; measurement of the sample by comparing it with a standard sample; simultaneous measurement of different samples and many others.
1. In a double focusing mass spectrometer comprising an electrostatic analyzer with adjustable power supply, a magnetic analyzer with adjustable power supply, at least one baffle with an aperture therein between said electrostatic and magnetic analyzers, an ion detector and a plurality of ion sources,
the improvement comprising means for guiding the plurality of ion beams emitted from said sources along a common path in a single ion beam to the electrostatic analyzer,
individually adjustable power supplies for each ion source, adjusting circuit means associated with at least one of the adjustable power supplies for adjusting the ratio of the ion source accelerating voltages and the electric field strength of the electrostatic analyzer, said adjusting circuit means including a control pulse generator for directing the adjusting circuit means for some period of time to pass more than one ion beam to the magnetic analyzer but for that period to pass no more than one ion beam from a given source continually to the magnetic analyzer and to pass the ion beam from at least one source intermittently to the magnetic analyzer. means associated with at least one of the adjustable power supplies for sweeping the ratio of the energy of the ion beams passing the electrostatic analyzer and the magnetic field strength of the magnetic analyzer such that the detector detects time shared multiple signals indicative of the mass to charge ratios of ions comprising the ion beams passed to the magnetic analyzer.
2. The improvement set forth in claim 1 wherein said adjusting circuit means adjusts the ratio of the each ion source accelerating voltage and the electrostatic field ad seriatim such that ion beams from each ion source pass in pulses to the magnetic analyzer ad seriatim.
3. The improvement according to claim 2, wherein adjusting circuit means comprising means for intermittently bringing the accelerating voltage of at least one power source to a reference voltage, said reference voltage being in the correct ratio with the strength of the electrostatic field to pass the ion beam to the magnetic analyzer.
4. The improvement according to claim 3 comprising a signal generator for determining the ion forming period, repitition frequency and phase thereof so that the ion beams do not pass through the electric field during the rise and fall times of the accelerating voltages.
5. The improvement according to claim 2 wherein said adjusting circuit means comprises means for fixing said ion source accelerating voltages at mutually different levels and for adjusting the intensity of the electric field in a repeated sequence so that the ion beams accelerated by said accelerating voltages are introduced into the magnetic field ad seriatim.
6. The improvement according to claim 5 comprising a signal generator for determining the ion forming period, repitition frequency and phase so that the ion beams do not pass through the electric field while the intensity of said electric field is being varied.
7. The improvement set forth in claim I wherein said adjusting circuit means adjusts the ratios of each ion source voltage and the electric field to permit the ion beam from one ion source to be continously passed to the magnetic analyzer and the ion beams from at least another ion source to pass in pulses to the magnetic analyzer.
8. The improvement according to claim 7 wherein the adjusting circuit means comprises means for bolding one ion source accelerating voltage at a reference voltage and the strength of the electric field to pass ions accelerated through the reference voltage and adjusting the accelerating voltages of at least another ion source to the reference voltage.
9. The improvement according to claim 8 comprising a signal generator for generating signals for determining the ion forming period of said ion sources, the repitition frequency, and phase thereof relating to said adjusting circuit so that the ion beams do not pass through the electric field during the rise and fall times of the accelerating voltages.
10. The improvement set forth in claim 1 comprising a signal processing circuit in synchronism with said adjusting circuit means for recovering signals indicative of the mass spectra of the ion beam from each ion SOUI'C8.