US2650306A

US2650306A - Mass spectrometer

Info

Publication number: US2650306A
Application number: US28163A
Authority: US
Inventors: Charles F Robinson
Original assignee: Consolidated Engineering Co Inc
Current assignee: Consolidated Engineering Co Inc
Priority date: 1948-05-20
Filing date: 1948-05-20
Publication date: 1953-08-25
Anticipated expiration: 1970-08-25

Description

Aug.- 25,. 1953 c. F, RoBlNsoN y 2,650,305

MASS SPECTROMETER Filed May 20. 1948 5 Sheets-Sheet l /ON/ZA T/ON CHAMBER E VACUAT/NG SYNCMQONOUS 5r ppgp yCHARLES EROB/NSON oma/E f la E swt/ TCH BY Aug. z5, 1953 V Filed May 20. 1948 C. F.` ROBINSON MASS SPECTROMETER RECORD/NG AT S/NGLE ACCELERAT/NG VOLTAGE FOR PEA/f A RECORD/NG ACROSS SMALL RANGE OF ACCELERAT/NG VOL TAGE FOR PEA/fk MAGN/ATUOE MAGN/TUDE THEORET/CAL PEAK AT ACCELERAT/NG VOLTAGE RECORD A' RECORD A" .47 VOL 7465 X T/ME /N SECONDJ` T/ME /N SECONOS F/O. 4A.

ThEORET/CAL PEAK B AT ACCELE/PAT/NG BREAKOFF T/ME /N SECO/VDS l'lME /N .SECONDS ,4r VOL TAGE Y INVENTOR. CHARL Es ROBINSON Aug. 25, 1953 c.;F. ROBINSON MASS SPECTROMETER Filed May 20. 1948 VArrow/vw Patented Aug. 25, 1953 UNITED STATES PATENT OFFICE MASS SPECTROMETER `Charles F. lltobinsm.,` Pasadena,` Calif., assignor to Consolidated Engineering Corporation, Pasadena, Calif., a corporation of California Application May 20, 1948, Serial No. 28,163

20 Claims. l

This invention relates to mass .spectrometry and more particularly to. an integra1 computing system for a mass spectrometer and especially for a continuous monitor mass spectrometer.`

A mass spectrometer is` an analytical apparatus which functions to. sortand measure ions. Ordinarily, it includes an ionization chamber in which molecules of the sample tope analyzed are bombarded by a stream of electrons and thereby converted into ions. The ions thus formed are propelled by so-called propelling or accelerating electrodes into andl through an analyzer chamber. During passage through the analyzer chamber, the ions are subjected to a transverse electric or magnetic. eld or both to` separate; `thel` @coording to-their :passato-.charge ratios. into a plurality of divcrging ion beams, each beam being com posed of ions of thesame specific mass and differm ing from the ions in theother beams. The diversins beams are successively focused, by adjustment of the` accelerating potential applied to theA accelerating clectrodesjon and discharged atv an `ion collector. The current produced 'cy each beam as it, strikes the ion collector is indicative of the amount of ions in the` beam and thus a measure of the partial pressure. of the molecules (from which the ionswcre derived) in the sample beine analyzed- In another type ci mess spectrometer the Several ion beams are oeueed on the Collector by variation f. the field iorees in. the analyzer Chember. ln this typ@ Qi` instrument the focusing is independent of the velectv of the ieri-S propelled into the analyzer chamber and thus of the accelerating potential. The present invention is applicable to both types of 1mass spectrometers.

In conventional practice the current produced by ion discharge at the ion collector is amplified in either an A. C. or D. C. amplier. The current magnitude is recorded as a continuous curve in a suitable recorder. The peaks in the record corresponding to the ions of differing specilic mass are referred to as mass peaks.

An important industrial application of mass spectrometry is, in the continuous monitoring' or` control of industrial processes. In this type of analysis a gas stream, as for example a plant A feed stream or an ellluent stream, is continuously or intermittently sampled. The composition l thereof with respect to one or` more, lout` generally less than all, of the components is determined on a substantially continuous basis. The continuity of analysis isof course a function of the frequency of sampling and, becomes continuous When a continuous sample stream is` introduced into the, mass r spectrometer. Continuous sample leaks have l change.

(Cl. Z50-41.9)

been developed for this purpose and form no part ofthe present inventio Generally in `this type of operation there is a certain previously selected composition.. which represents an optimum for the speciiic process involved.; a mixture having such a composition may be referred to as a standard sample although it is not necessary for the purpose: of this invention `that suchsamples exist in fact. Itis important to detect deviations from thesta-ndard as quickly as possible so as to correct the process variables which are responsible for the variation in compositionA conventional mass spectrometer Whichis subject to zero shifts or overall sensitivity fluctuations. adds these inherent variables to the monitoring operation which may mask or accentuate changes in composition of the sample stream itself.

I have now provided a so-called integral or internal computing circuit by means of which themess pea-ksbeiue monitored may be seperate- 1y attenuated This separa-te attenuation `.filaires it possible to upset the nature-1 abundance ratios of the `masses merely by separate adjustment of the attenuation.` Thus strong peaks may be attenuated sufficiently to bring `all of the peaks somewhere near the middle of the record scale l and all of the` peaks may be so adjusted that they will all be equal when the mass spectrometer analyzes a sample having the standard composition. Y

If the peak heights for the components being monitored are established at equality, that equality is preserved independently of zero shifts or overall sensitivity changes in the mass spectrometer and is upset only by an actual pattern Thus anydeviation of the several peaks from equality Wil1 .be a reliable indication of a change of the relative abundance of the particular mass or maSSes in the sample. JAdditionally the magnitude of the change Will be evidenced by the relative deviation of the `peak from equality i and may be easily interpolated into devi-ations in sample composition by proportionate` calculation.

The mass spectrometer of the invention may include` a conventional ionization chamber with `an associatedelectron gun` and `accelerating electrodes, `an analyzer chamber having a collector electrode in the path of the ions dscharsed'from the ionizationchamber, means for indicating or recording the current striking the electrode` which may include an amplifier for increasing the colvoutput currents responsive to the proportion of one or more constituents in a sample undergoing analysis will be subject to zero drift and overall sensitivity changes which will impair its use for continuous monitoring. The present computing or attenuating circuit provides means for automatically eliminating Vthe effects of such zero v shifts or overall sensitivity change on such continuous analyses.

In essence, the circuit of the invention com Y prises a plurality of separate 'output channels for the current developed at the collector by separate ion masses successively focused on the collector. Each output channel includes separate means for attenuating the voltage carried in that channel and all of the output channels are separately connected to a single sensing meansV for successively sensing the separate attenuated voltages applied thereto from the plurality of output channels.

The term sensing means as employed herein contemplates recording, indicating, or signalling means adapted either to sense the successive mass peaks as such or to differentially sense only variations between the mass peaks.

Additionally in a preferred embodiment of the invention the circuit includes a source of constant voltage connected across a plurality of parallel coupled potentiometers which function to successively supply differing potentials to the accelerating electrodes or to the analyzer field depending on which is Vused for focusing. To simplify the description the standard voltage is referred to as focusing voltage and the potentials set up on the severalpotentiometers as focusing potentials. Automatic means coupled to' the last mentioned potentiometers andthe separate attenuating means serve to simultaneously shift the output channel in which the output voltage Vis channeled at a given time interval :simultaneously with a shift in focusing potentiaL Y Conveniently for recording purposes a given focusing potential is applied to the accelerating electrodes or field for a period of several seconds and similarly Vthe output voltage `from the ion collector is' applied to a given output channel, corresponding to the particular applied focusing potential for a like period.

In one embodiment of the invention the means for simultaneously shifting the energized output channel and applied focusing potential comprises a stepper switch, coupled if desired through suitable relays to the focusing potentiometers and to the several output channels. The stepper switch may be manually operated but is more Y conveniently automatically operated by a motor driven cam or other means familiar in the art. Y Alternatively the several focusing potentiometers may be coupled to one level of a multi-level Vstepper switch andthe several output channels may be vconnected to another level of the same stepper switch, the various levels of the stepper 1 switch operatingV in unison to synchronize the :i shift .in focusing potential and corresponding output channels.

The number of components of the sample which it is desired to analyze will determine the number of output channels to be included in the circuit of the invention. The number of potentiometers associated -with the source of standard voltage and adapted to supply the focusing potentials will be similarly determined. Thus the circuit includes one output channel and one focusing potentiometer for each mass peak of the sample to be analyzed, and may include any number desired, the number of mass peaks and the number of chemicallyrdistinct components being, in general, different.

The invention will be more clearly understood byl reference to the following detailed description of the several embodiments thereof as taken in conjunction with the accompanying drawing in which:

Fig. 1 is a diagrammatic illustration of the conventional mass spectrometer;

Fig. 2 is a circuit diagram of the computing circuit of the invention as applied to the mass spectrometer of Fig. 1;

Fig. 2A is a partial circuit diagram showing a modification in the circuit of Fig. 2; Y

Figs. 3 and 3A show a typical record as'obtained from a circuitV such as that shownrin Fig. 2A, showing the results of fluctuations in the voltage of the focusingvoltageisource;

Figs. 4 and 4A show a typical record as obtained from a circuit such as that shown in Fig. 2, showing the results of fluctuations in the voltage of the focusing voltage source.

Fig. 5 is a circuit diagram illustrating various modifications which may be incorporated in the circuit of Fig. 2 for the accomplishment of the Y Y objects of the invention.

In the drawings the invention is shown in association with a mass spectrometer of the type wherein the ion beams are focused byY varying the potential applied to the accelerating elec-Y trodes. As pointed out above and as will be apparent from the following description, the invention is equally adapted to incorporation in a mass spectrometer wherein the ion beams are focusedV by variation in the applied field forces.

Referring to Fig. 1, it will be observed that it shows a mass spectrometer having an ioni-V zation chamber Il, an analyzer tube I2, and an ion collector I3 disposed within an envelope I4 which is-kept at low pressures during the operation of the instrument.

The spectrometer is provided with a pumping system or envelope exhaust line l5, which may be connected with a mercury diffusion pump, molecular pump, or any appropriate evacuating system not shown.' The analyzer tube l2 may be provided with ports i8, by means of whichV the ionization chamber and the analyzer tube are evacuated through the envelope I4. Alternatively the envelope may be omitted by making the analyzer tube i2 gas-tight and attaching the pumps to it by means which are well known. An inlet line 2l provides means for introducing a sample to be analyzed either continuously o r S1' being many' modifications' thereof', equally ap# plicable to this invention; y

As above' described, the `i"onspropelle l` from the: ionization chamberare formed in the` analyzer tube into diverging beams of ions of ai given specinc mass. These diverging' ion beams are successivcly focused on the on collector I3 by varying. the potential applied to theacce'lerating elec`` trodes. The ion collector I3 is linked"r with the amplication and computing circuit (Fig. 2') by a lead s`ealed through the` Wall of the envelope I4:. The lead" 20` may connect the collector il? to' an amplifier 22 or' alternatively the lead' 2U may be connected' directly to the computing circuitif the ion current at collector I3 is ofsuch magnitude as not to require furtheramplieation as in the embodiment of Fig. 5.

Referring now'A to. Fig. 2i whichi shows one" em-` bodiment of the' computing circuitiin accordance With the invention',` it"\".rill"b'e observedthat a pluralityof `adjustahle tap potentiometers P4; PF, aI'dP'G` are' c'onlleclcolin` parallel tothe 'ampliflei'" `2`2`; One side. of each of the pot'ehtiometers is connected to a' sensorI 2li; andI4 adjustabletaps :52h, and 2'1 f' the potelticmeters' F4, P5", Aand Grespectively are. each connected to' one pole of one. ofA a plurality' of: douhle pole relays R1', R2, and respectively; l

rllhree adjustable "tap potentioriieters' Pl, P2, P31. are connected" iii parallel across an accelerating voltage source the adjustable taps 3 32; and 33 of me respective potentiometer-s P l; Pzgana Pt, each being eminentes te me other poleof one ofthe douhle pole relaysRl, R2, and R3 respectively. One side` of the' accelerating voltage. source is.` connected through a rheostat 3'6 to.. the. accelerating electrodes (see Fig. l) in the: mass spectrometer ionization chamber il; One pole.A of each ofthe relays. RI, Rlland R3`- is, connectedtothe sensoru 24',` 'thejother pole of eachof therelays being connected to the mass .spectrometer ionization chamber Il?, In this manner eachof the potentiometers lflql,"` and P6 is connected` to the sensor and" each of the potentiometers Pl',4 E2) andP`3` is connected" to thefionization chamber through the relay" A stepper switch 3l. is connected in seriesbe'e' tween an electrical supply line 3E one of: eachl of. the relay coils 394'0" and" 4l which are connectedto terminals 39A, liQA'Qan'd lflA respectively of the stepperV switch. The other.

side ofleach. of the` relayrcoils is connected to thefotherA side 42 Aof the electrcalsupply line.

The stepper switch 3l an'd'tl'ie rheostat 36 are operated synchronously `either "manually or" by a The synchronous drive is motor driven. cam. represeluted by the dotted'line 4. Inoperation the switch arm 31A of the stepper switch.A is stepped at predetermined intervals which Ineed not be the same and is' connected `successivelyl with the Contact points I39A, 40A, and `IWA' energizing the respective coils` 39,402 and 4"l ofthe relays Rl, R2,"and"R3";" Wlierrthe" relay Rlis energized the potentiometer Plfis" con nected'to the: accelerating electrodes in vtheioni- `zal-ion` chamber impressing anv accelerating volt` age thereondetermined by thesetting of the adjustable tap` 3l. A't the same `time'the poten#- tiometer"P4"' is connectedto` thefsensor 24 and as the' ion beam' of",` a spe-cinc mass determined by, the. applied accelerating'voltage is'` discharged at" the ionn collector' `{"3, stheresultant` current 4is amplified mthsampuner-"zzf attenuated-in me potentiometer P4 to:arrext'ent'dependent` upon the setting" of" the 'adjustabletap' 2'5`, and tsensed' in-` the se'riso'r24. S*uccessivelyA` the stepper" "cli" 31 `actuates the relays 4Q and* 41| connecting the potentiometers P2 and P3-tothe ionization chant-v ber and me potentiometers P5 and Pe to' tile sensor` Thus as different potentials are iin pressed on the accelerating electrodes" of the mass spectrometer by successive connection thereof with' the potentomters PI, P2 andl P3, theV ions of masses corresponding to uthese potentials` and focused onf the collector I3` responsive to the varying accelerating potentials are separately1 at-r tenuated by means ofthe p'otentiometers1554,- and P6 prior t`0` sensing in the sen'sbAI" 24. AS mentioned above the sensor 24" may lbe a cone tinuous recorder, ai meter, a differential signalling device or the like. Selection of the typeof sensing device toemploy Willy be governed by eachapplication of the instrument.

Whenmonitoring a plant process in which it is desired to control the proportions of compo|`J nents A, B, and C', for example, theN adjustable taps 3|, 31 and 33 `ofthe potentiom'eters Pl, P2, and P3 respectivelyare set so as to separately focus the ions `of components A, B, andA C' ori the collector; The potentiometersPl, P2, and" P3, are successively connected to the accelerate' ing" electrodes by revolution `of the switch" arm 31A of the stepper switch 31; By proper" setting ofthe adjustable'taps 25,26 and 2K1 vof' the respective potentiometers P4, P5, and P5 the mass peaks of each ofthe components A, B, and C may be equalized withrespect to` thesensor 24. Although components"A,.B`, and C may be and usually are present in the sample stream in differing proportions,th`e recorded"mass peaks for each may be made equal. n If the potentiometers P4', P4, and PB are' setso that the mass peaks of the several `corr'iponents Will be equal, any deviation from. equality will indicate a change in the abundance ratioof the components A, B, and C4 in the sample stream. Such indication Will" beindependent of zero shift or of; overall change in sensitivity the spectrometer, neither of which `factors will disturb the equality established betweenthema-ssA peaks."`

InFig. 2A a portion of the circuitV of Fig. 2

including the accelerating voltage supply' and the' potentiometers P'I, P2 and P3 is shown as it might' befincludedin the circuit of Fig. 2.` i The dife' ferentiating feature of that portion of the'cir` cuit shown in Fig. 2A is the elimination of the rheostat 36. The difference in results arising fromthe use' of a circuit including that portion shown in Fig. 2A and a circuit shown in Fig. 2'; is illustrated in Figs. 3; 3A, 4' and 4A. llilrnploying an accelerating" voltagel supply circuit as shown in Fig. 2A the constancy of the voltage supply `is highly critical. The elect of small uctuation in the supply voltage: is illustra-ted diagrammatically inFigs. 3"and` 3A which show" a typical record. Referring to these gures; the dotted line trace" 5lllis^indicative of a theoretical would appear if the outputlvoltage ofl the ion collector wasrecordedfrombeginning to end of the peak. The solid curve 5i (Fig:` 3l) illustrates' the type of curve obtained with axed acceleratJ ing voltage X which representsA the` standard voltage as applied from the" voltage source through potentiometer P i, for example;

Now if ,theVoltagellsourceliluctuatesf so? that' thefactualgaccelerating voltage isv slightly "different from*` the voltage X, as forlexamplevthe voltage (Fig. 3A) the` component "A lvvil'lvgive 7 acurve 52 peaked reduction in peak height has been due to fluctuation 'in accelerating voltage.

.Figsf iV and 4A illustrate the type of record obtainedusing thercircuitV of Fig. 2 including the rheostat 36. Referring again to Fig. 2 the'rheostatand the stepper switch 31 are synchronized so .thatV at each setting of the switch arm 31A the arm 36Aof therheostat 36 will make oneV complete revolution so' as to vary theresistance in series over the complete range of the rheostat. This in effect gives a small variation in accelerating voltage on either sideV of the fixed value established by the voltage source 30 and the respective potentiometers Pl, P2, and P3. The effect of this small variation in accelerating voltage isillustrated in Figs. i and 4A. The theoretical curve 50 for component A is again shown. The Vcurve 5|A (Fig. 4) villustrates the type of record obtained when the accelerating voltage varies" an equal amount on either side of the constant voltage as established by the voltage source and the potentiometer PI, for example. By reason of this voltage variation', Ythe top of the peak 5IA is curved in conformity with the theoretical peak 5i).V This is to be compared with the changes slowly and continuously through a small interval during the time that a given mass peak is being recorded, it being immaterial whether,

this slow change is brought about by a variable resistor, a condenser discharge, or other means which will occur to those familiar with the art.

Modifications may be made in the attenuating or computing circuit without changing the function or effectiveness thereof. Several such modifications are illustratedY in the circuit diagram of Fig. 5. Referring to Fig. 5, it is seen that the amplifier 22 may b'e eliminated in which case a series of amplifiers AI, A2, and A3 are connected in parallel across the collector and ground. l

The amplifiers Al, A2, and A3 replace the'potentiometers P4, P5,` and P6 of the circuit of Fig. 2 and serve the same function.V ThusV the voltage developed at the ion collector by successive mass peaks are separately and successively ampliiied in amplifiers Al A2, and A3 which may be adjusted or established so that the recorded peaks of the several specific masses are equal or bear Vsome other desired relationship to each top of the peaki in Fig. 3, which is flat by reason of the fact that the accelerating voltage Y Y is fixed at a singleV value.

`In Fig. 4A it is assumed that the, voltage source has .fiuctuated so vthat the voltage delivered to the" accelerating electrodes is Yrinstead of X and accordingly therecording trace extends ,on

. either side of the voltageY equidistant with respect toy time. It is' immediately apparent by examination of a record such as that shown in Fig. '4Aithat the voltage source is in' error mas-VV Y much as the trace lhas `not peaked prior to the break'offpoint. If the increment between the voltages X and Y isrsuiiiciently small that the curve obtainable across accelerating voltage Y forfexample, does actually reachtlie peak and begin its downward travel, thecorrect readings will be obtained even though Ythe voltage source has fluctuated. However, if the increment between voltages X and Y is suiiiciently great Vthat the recorded trace does not peak before the break .off'poinh the fact of an error in source voltage is immediatelyapparent.V In the circuit ofFig. 2,' the rheostat serves to permit visual observation of Vfiuctuatio'ns inV the voltage and does not leave theroperator to a guess as to the reason for changes in peak height. Y

l Thus the inclusion of a rheostat in the ac.

Vvoltage fiuctuation` so that any changes in the recordrnay Ibe properly attributed thereto. It

other. i The amplified output from the amplifiers Al, A2, and A3 is connected to a sensor 60 through one level Sl of a multi-level stepper switch 62. An accelerating voltage source 64 is connected across a series of parallel coupled potentiometers PI, P2, and P3, the adjustable taps 65, 66 and 61 of which are connected through a second level S2 of the stepper switch 62 to the accelerating electrodes (not shown) in 'the mass spectrometer ionization chamber ll. By synchronizing rota'- tion of the

switch arms

62A, 62B, ofthe two levels of the stepper switch 62, a separate output channelis linked to the sensor for each accelerating potential applied to the accelerating electrodes through the potentiometers Pl, P2, and P3.

Thus, at an Vaccelerating potential determined.V by the setting of the tap 65 of the'potentiometerV Again, a rheostat 'l0 is connected in series with the accelerating voltage source and is driven synchronously with the stepper switch B2 so that with each setting of the stepper switch arms the rheostat arm 10A will complete a revolution.

and A3 may be connected in parallel across either` a mass spectrometer amplifier orrthe mass spectrometer ion collector. Similarly any number of accelerating potential determining Vpotentiometers may be connected in parallel across asource of constant voltage. In this way the circuits may be altered by the addition of Vsupplementary attenuating devices and `accelerating potential determining potentiometers so as to provide an l internal computing circuit adapted to sense and 'I'he essential feature of the invention is that the natural abundance ratios of the mass peaks to i fbe monitored may be upset in a controllable way and it is immaterial whether all the peaks are amplified by different amounts, all attenuated by different amounts, or some attenuated and others concurrently amplied.

For purposes of eliminating the effects of zero drift and overall sensitivity change the circuits of Fig. 2 or 2A are to `be preferred over that ofl Fig. 5. Since most of the zero drift and sensi- :tivity change encountered in mass spectrometer operation is attributable to the amplification system, it is apparent why the circuit of Fig. 5 will be susceptible to these errors. However, in applications where these `factors are of little or no importance, the `circuit of Fig. 5 is acceptable.

I claim:

l. In a mass spectrometer havingan ionization chamber, an analyzer, an ion collector, means .for ionizing molecules in the ionization chamber and electrically energized means to establish a :field in the .analyzer `adapted `to focus ions of .diiering `specific mass on the ion collector responsive to variations in the magnitude o1 the .electrical impulses applied thereto, the improve- .,ment which comprises a source of constant voltage, means for supplying different voltages from the source to said electrically energized means, `a plurality of `output channels adapted to carry .the separate output voltages developed at the collector responsive to discharge of ions of diftering specific mass at the collector, separate means .in each output channel or changing the magnitude of the voltage carried in that channel, andsensing means for sensing the output voltages of each channel.

2. In a mass spectrometer having an ionization chamber, an analyzer, an ion collector,

means for ionizing molecules in the ionization chamber, and accelerating electrodes for propelling ions from the ionization chamber to the collector, the 4improvement which comprises a source of constant voltage, means associated with the source of constant voltage for `impressing successively diierent potentials on the accelerating electrodes from the source of constant voltage, a plurality of output channels adapted to carry output voltages from the collector, separate means in each output channel for changing the magnitude of the voltage carriedin that channel, sensing 1means Jfor sensing the output voltages of each channel, and means for selecting a separate one of said output channels for each of said different potentials applied to the accelerating electrodes.

3. In a mass spectrometer having an 4ionization chamber, an analyzer, an ion collector, means lfor ionizing molecules in the ionization chamber, and accelerating electrodes for propelling ions from Vthe ionization ychamber to the collector, the improvement which comprises a source of voltage, a plurality of adjustable tap potentiometers connected in parallel across the source and to ,the `'accelerating electrodes for impressing successively different potentials on the accelerating electrodes., a plurality of output Vchannels adapted to carry output voltages from the collector, separate means in each output channel lfor changing the `magnitude of the voltage carried in that channel, sensing means for sensing the output voltage of each channel, and selecting means for selecting a separate one `of .said

output channels foreach of said .different potentials applied to the accelerating electrodes.

4. Apparatus according to claim 3 wherein the selecting means comprises a `plurality .of double pole relays alternately energizable through a stepper switch, a separate one of the relays being connected in series between` each of said output channels `and .the sensing means, and .between each of said potentiometers and the accelerating electrodes.

5. Apparatus Vaccording to claim 3 wherein the selecting. means comprises a multi-level stepper switch, one level thereof being connected between the sensing -means and output channels so that each of the output channels is connected to `a separate terminal .of the switch, `a second level .of the switch being connected between .the accelerating electrodes` and the potentiometers so that each potentiometer is connected .to a separate terminal of the switch.

6. In a `mass vspectrometer having .an ionization chamber, an analyzer., an ion collector, means for ionizing molecules in the ionization chamber, and accelerating electrodes `for .propelling ions from the ionization chamber to the vcollec- `tor, the improvement which comprises `a source of voltage, a plurality of adjustable .tap potentiometers connected in parallel across the source,

`means for successively connecting a separate `one of` said potentiometers .to the accelerating electrodes for impressing successively diierent potentials on the accelerating electrodes fora `given .time interval, a rheostat connected inseries between the source `and the potentiometers .so as to vary the voltage applied to the potentiometers from the source, means for .causing the rheostat vto vary through its full range within said time interval, a plurality of output channels adapted to carry output voltages from the collector, separate `means in `each output channel for changing the magnitude of the voltage carried in that channel, sensing means for sensing the output voltage of .each channel, and selecting means "for selecting a separate one of said output channels foreach of said different potentials applied to the accelerating electrodes.

7. In `a mass spectrometer having an ionization chamber, an analyzer, an ioncollector., means for ionizing molecules in .the ionization chamber, and accelerating `electrodes for propelling ions from the ionization chamber to the collector, the improvement which comprises a source vof constant voltage, means associated with the source of constant voltage for sequentially impressing different potentials on the accelerating electrodes, a plurality of output channels adapted to carry output voltages from the collector, an adjustable top potentiometer in each channel for attenuating .the voltage carried in that channel, sensing means for sensing the voltages attenuated by said potentiometers, and means for selecting a sepay'rate one of said .output channels for each of said `different potentials applied to the accelerating electrodes.

8. In a mass spectrometer having an ionization chamber, 'an analyzer, anion collector, means Vfor ionizing molecules in the ionization chamberandaccelerating electrodes for propelling ',tor, the improvement which comprises a source, ,ofr constant voltage, separate means associated' with the source of constant Voltage for sequen- .ions from the ionization chamber to the collectially impressing diierent potentials on the acl celerating electrodes, a plurality of output channels adapted to carry output voltages from the ing a separatelone of said output channels for each of said different potentials applied to the L accelerating electrode.

. 9. Apparatus according to claim 8 wherein the selecting means comprises a plurality of double Y connected to one pole of a separate one of said Y pole relays, each of said output channels being relays and to the sensing means through the relay, the separate means for impressing different potentials onthe accelerating electrodes being convoltage.

nected through the other pole of each of said relays to the accelerating electrodes, and a stepper switch connected in series between the coils of said relays and a separate source of energizing 10. In a mass'spectrometer having an ioniza- ,tion chamber, an analyzer, an ion collector,

means for ionizing molecules in the ionization chamber, and accelerating electrodes for propelling ions from the ionization chamber to the ',collector, the improvement which comprises a source of constant voltage, a plurality of adjust- Vable tap potentiometers connected in parallel across the source and to the accelerating electrodes for impressing diierent potentials on the accelerating electrodes, a plurality of output ,channels adapted to carry output voltages from the collector, a separate adjustable tap potentiometer in each output channel for attenuating the voltage carried in that channel, sensing means for sensing the attenuated voltages from said f, last named potentiometers, and means for selecting a separate one of said output channels for each of said diierent potentials applied to the i accelerating electrode.

11. In a mass spectrometer having an ioniza- ,tion chamber, an analyzer, an ion collector, means for ionizing molecules in the ionization chamber, and accelerating electrodes for propelling ions from the ionization chamber to the collector, the improvement which comprises a source of constant voltage, a plurality of adjustable tap potentiometers connected in parallel-across the source and to the accelerating electrodes for imthe amplifiers, and meansfor selecting a separate one of said output channels for each of said different potentials applied to the accelerating electrode.

12. In a mass spectrometer having an ioniza- VtionY chamber, an analyzer, lan ion collector,

means for ionizing molecules in the ionization chamber, and accelerating electrodes for propelling ions from the ionization chamber to the collector, the improvement which comprises means for providing voltage which varies periodically about a xed level, a plurality of adjustable tap potentiometers connected tosad voltage supplyferent potentials on the electrode for a given time Y interval, that time, interval being the same as one lperiod of variation; of the Vvoltage supplying Y means, a plurality of output channels adapted to Y carry Youtput voltages from the collector, separate means in each output channel for changing the magnitude ofthe voltage carried in that channel, sensing means for sensing the resultant voltage, and selecting means for selecting a separate one of said output channels for each of said different potentials applied to the vaccelerating electrodes.

13. A circuit for a mass spectrometer adapted to be coupled to the collector electrode ofl the mass spectrometer and comprising a plurality of output channels adapted to separately carry the Y separate output voltages developed responsive to discharge of ions 4of differing mass-to-charge ratio at the collector electrode, separate means in each output channel for adjustingthe magnitude of the voltage carriedrin that channel and sensing means for separately sensingthe voltage output of each channel. M

, 14. A circuit for a lmass spectrometer adapted to be coupled to the output of the mass spectrometer and comprising a plurality of output channels adapted to separately carry the separate output voltages developed responsive to discharge of ions of differing mass-to-charge ratio, means for feeding the different output voltages of the mass spectrometer into separate ones of said output channels, separate means in each output channel for adjusting the magnitude of the voltchamber, accelerating electrodes for propelling ions from the ionization chamber through the analyzer to the ion collector, and an amplifier for amplifying output voltages from the collector, the improvement which comprises a plurality of output channels adapted to separately carry the separate output voltages from the amplier developed responsive to discharge of ions of differ- I ing Vmass-to-charge ratio at the collector, separate means in each output channel for adjusting the magnitude of the voltage carried in that channel, and means for separately sensing the output voltage of each channel.

16. A circuit for a mass spectrometer adapted to be coupled to the outputof the mass spectrometer and comprising a plurality'of output channels adapted to separately carry the separate output voltages from the mass spectrometer, separate means associated with each output channel for adjusting the magnitude of the voltage carried in that channel, and sensing means for separately sensing the voltage-output of each channel.

17. A circuit for a mass spectrometer adapted to be coupled to the output amplifier of the mass spectrometer and comprising a plurality of output channels adapted to separately carry the separate output voltages from the output amplifier, means for feedingY the separate output voltages from the mass spectrometer amplier into separate ones of said output channels, means for adjusting the magnitude of the voltage carried in at least one of said channels, and sensing means for separately sensing the voltage output of each channel.

18. In a mass spectrometer having a collector electrode, means including accelerating electrodes for causing ions of particular mass to strike and discharge on the collector electrode. means developing an ouput voltage related to the number of ions of a given mass striking the co1- lector and means for supplying a potential to the accelerating electrodes, the combination comprising means operable to successively vary the potential applied to the accelerating electrodes whereby ions of different mass are successively focused on the collector electrode and a separate output voltage is developed for each mass, means operable to separately alter the magnitude of at least one of the output voltages, and means for sensing the several voltages including the altered voltage.

19. In a mass spectrometer having a collector electrode, means including accelerating electrodes for causing ions of particular mass to strike and discharge on the collector electrode, means for supplying a potential to the accelerating electrodes, and means developing an output voltage related to the number of ions of a given mass striking the collector electrode, the combination comprising means operable to successively vary the potential applied to the accelerating electrode by which means ions of diierent mass are successively focused on the collector electrode, means operable to establish the output voltages produced responsive to the ions of each separate mass in a predetermined relationship and means sensing the resultant voltages.

20. In a mass spectrometer having a collector electrode, means including accelerating electrodes for causing ions of particular mass to strike and discharge on the collector electrode, means for supplying a potential to the accelerating electrodes, and means developing :an output voltage related to the number of ions of a given mass striking the collector electrode, the combination comprising means operable to successively vary the potential applied to the accelerating electrodes whereby ions of diierent mass are successively focused on the collector electrode, means adjusting the output voltages produced responsive to ions of each separate mass, and means varying the output Voltage adjustment responsive to variation in the potential applied to the focusing means, and means for sensing the resultant voltages.

CHARLES F. ROBINSON.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,331,190 Hipple Oct. 5, 1943 2,370,631 Berry Mar. 6, 1945 2,380,439 Hoskins et al July 31, 1945 2,470,745 Schlesman May 17, 1949 2,476,005 Thomas July 12, 1949 OTHER REFERENCES Smith et al., Review of Scientific Instruments, February 1937, vol. 8, pp. 51-55.