US3602709A

US3602709A - Mass analyzer including magnetic field control means

Info

Publication number: US3602709A
Application number: US713232A
Authority: US
Inventors: Charles W Hull
Original assignee: Bell and Howell Co
Current assignee: Bell and Howell Co
Priority date: 1968-03-14
Filing date: 1968-03-14
Publication date: 1971-08-31
Anticipated expiration: 1988-08-31

Abstract

An electronic mass analyzer. The analyzer comprises an electrical discharge source of charged particles, a peak selector system that controls the analyzer magnetic field and an electronic collecting system. Charged particle beams from the source are brought into register at an electronic collector by the peak selector without reference to the beams being detected. The addition of suitable control circuitry adapts the analyzer to programmed operation.

Description

United States Patent [72] inventor Charles W. Hull Sierra Mldre, Calif. [211 App]. No. 7 13,232 [22] Filed Mar. 14, 1968 [45] Patented Aug. 31, 1971 [73] Assignee Bell & Howell Company Chicago, Ill.

[54] MASS ANALYZER INCLUDING MAGNETIC FIELD CONTROL MEANS 17 Claims, 5 Drawing Figs.

[52] US. 250/4l.9 ME, 313/230 [51] int. (I 1101] 39/34 [50] Field 01 Search 250/41.9 S, 41.9 SB, 41.9 SA, 41.9 SE, 41.9 R; 313/23, 236

[56] References Cited UNITED STATES PATENTS 2,659,821 11/1953 Hipple 250/41 .9

3,270,773 9/1966 Brunnee 250/4 1 .9 S

3,337,737 8/1967 Eberhardt 250/207 3,405,263 10/1968 Waniess et al. 250/41.9 lSE 3,416,073 12/1968 Gutow 250/41.93

OTHER REFERENCES Physical Review, Vol. 55, May 15, 1939, Allen, Pgs. 996 to Primary Examiner-James W. Lawrence Assistant Examiner-A. L. Birch Attorney-Christie, Parker and Hale COLL E C 7'04 654 M ON/ TOE wrssa en 10 2 AND awmevm BEAN MON! TOR Mil-K 64647119 PATENTEI] was] ISII SHEET 1 BF 3 PATENTED M1831 l97l SHEET 2 BF 3 MASS ANALYZER INCLUDING MAGNETIC FIELD CONTROL MEANS BACKGROUND OF THE INVENTION This invention relates to mass analyzers and in particular to electrical discharge source instruments operated on an electronic basis without the use of photoplates as detectors.

In general, because of the spread of energies and the angular diversity of charged particles produced by an electrical discharge source also known as a vacuum breakdown source,

such as described in Advances in Mass Spectrometry, Vol. III, Ed. W. L. Mead, page 109 (Institute of Petroleum, 1966), it has been found that double-focusing mass analyzers are most suitable for use with such sources in order to successfully resolve and analyze the elements in a solid sample, In typical double-focusing mass analyzers a radiofrequency spark source for the production of charged particles is arranged preceding the entrance end of an electric analyzing sector. Interposed between the source and the electric sector is one or more accelerating electrodes for propelling charged particles generated by the spark source into the electric sector where the particles are resolved for their velocity diversity. The particles emerge from the electric sector and enter a magnetic sector and are deflected into beams such that they assume characteristic radii of curvature depending upon the mass of the various particles in the sample. Subsequent to deflection under the influence of the magnetic field the particles are caused to impinge on a photographic plate which is removed from the analyzer subsequent to the analysis and developed. After development the photoplate and the information recorded thereon is analyzed to determine qualitative and quantitative information about the samples under analysis based on the relative spacing and intensity of the indicia on the developed plate.

Such an analyzer is characterized by a relatively long operating time in order to obtain a meaningful indication at the photographic detector. This is due to the necessity of exposing the photoplate detector to the charged particle or ion beam for substantial periods of time to permit a sufficient number of charged particles to register on the plate to produce visible indications upon development. In addition to the length of its cycle operating time this type of analyzer has an inherent maximum sensitivity which cannot be increased.

Heretofore analysis with this type of instrument has been done in approximately the following manner. A simple to be analyzed is placed in a prepared analyzer and an analysis run. Subsequent to completion of the analysis the photographic detector is examined and compared to the data on previously developed plates for samples of known composition. Knowing the operating parameters of the analyzer and comparing the plates having known and unknown data, the operator can determine the identity of the elements in the unknown sample and, to some extent, the quantities present of the identified elements. Heretofore no solids-analyzing instrument has been available which can be readily adjusted to examine a sample for the presence of one or two elements of interest and which embodies the further capability of accurately measuring quantitative information about the element under consideration.

SUMMARY OF THE INVENTION The present invention provides a mass analyzer capable of accomplishing the tasks described immediately above and provides, in addition, a mass spectrometer readily adaptable to automatic operation. The invention comprises a source of charged particles to be analyzed. A magnetic field analyzing sector is located in the path of the particles from the source for separating particles from the source according to their respective masses. A collector is provided at the exit end of the magnetic field sector for receiving particles of a predetermined mass and means for controlling the magnetic field of the sector is provided to bring particles of the predetermined mass into register at the collector. Electrical circuit means is connected to the collector for providing data regarding the particles collected at the collector.

The present invention provides a new method of developing qualitative and quantitative data in the field of electrical discharge charged particle spectra analyses, eliminating -or reducing some of the inefficiencies and time consumption inherent in the photoplate method of analysis. The method of this invention can be performed faster than the photoplate method and offers the additional advantage that when an analysis is complete the data is immediately available and in quantitative form. This means that the cost per analysis is greatly reduced, making an instrument operated according to the method a more attractive general analytic tool. The method of the invention will be referred to herein as an electronic method of analyzing electrical discharge source spectra or simply as an electronic method of mass spectra detection.

The electronic method is characterized by increased sensitivity in comparison to the sensitivities previously available with double-focussing instruments. Significantly lower ion currents are needed in the electronic version in order to detect a given concentration of an element, e.g., one part per billion, in comparison to photoplate detection. Such increased sensitivity also means that a given element can be detected more rapidly with the electronic method. By virtue of the increased sensitivity an electrical discharge source instrument can now be more fully utilized in such applications as trace analysis. The electronic method of the present invention also makes an electrical discharge source analyzer directly adaptable to automatic operation. Equipping an automatic or programmed analyzer with a multiple sample holder and a clean, ion pumped source housing enhances the value of the instrument as an analytic tool by now making a number of materials research problems more practical.

BRIEF DESCRIPTION OF THE DRAWINGS These and other advantages of the present invention will be better understood by reference to the following FIGS. wherein:

FIG. 1 is a schematic illustration of an analyzer according to the present invention;

FIG. 2 is a sectional view of a charged particle source for use with the apparatus of the present invention;

FIG. 3 is a sectional view of a magnetic field analyzing sector for use with an analyzer according to the present invention;

FIG. 4 is an electric schematic diagram illustrating one form of control of the magnetic field of a magnetic field analyzing sector of a mass analyzer; and

FIG. 5 is an electrical schematic view of a magnetic field control element utilizing a Hall effect device.

An embodiment of the present invention is illustrated in FIG. 1. In that FIG. an electrical discharge source 10 of ions is disposed adjacent the entrance end of an electric analyzing sector 12 of a double-focusing instrument 8. Source 10 includes a pair of spark electrodes 15 composed of a material to be analyzed. The electrodes are connected to a power source 17 which provides the electrical energy for sparking the electrodes and creating a supply of charged particles. In the embodiment of FIG. 1 the power source is typically a radiofrequency oscillator. Other electrical discharge types of sources are also contemplated for use with the present invention, the other types including those of the high voltage pulse type and the high current are type. In the former a charged particle creating electric arc is initiated by a high voltage pulse, while in the latter an arc is initiated by vibrating the electrodes so that they alternately touch and arc.

Charged particles created by a discharge in source 10 are accelerated by electrode 22 and enter electric analyzing sector 12. Sector 12 in turn is arranged to direct particles emerging therefrom into a magnetic analyzing sector 14. Upon exit from sector 14 transmitted ions are caused to impinge on a collector 16.

As will be discussed in more detail in connection with FIG. 2, a supply 18 of a gas having a simple spectrum is connected to source for providing a supply of reference particles for calibrating and aligning the instrument prior to operation of the main electric discharge source. Charged particles emerging from sector 12 pass a total-beam-monitoring electrode 24 before entering sector 14. Located within the magnetic field generated within sector 14 is a device 26 for controlling thestrength of the magnetic field to thereby control the mass of the particle directed through an exit aperture 28 from sector 14 and thence to collector 16. A preferred embodiment of the collector is an electron multiplier, the output of which is fed to collector beam monitor, integrator, and signal comparator 30 where the fraction of the charged particle beam detected at collector 16 is compared to the total charged particle beam entering the magnetic sector as detected by electrode 24 and as indicated by a total beam monitor integrator 32.

Because of alignment and calibrations problems inherent in an electrical discharge source instrument it has been found useful and convenient to provide an auxiliary supply 18 of particles in addition to the primary electrical discharge source will put out a steady beam of charged particles of known mass. Such an arrangement is illustrated in FIG. 2. In that FIG. a bottle 34 of sample gas is connected by means of a valve 36 to a capillary leak 38. The leak is connected by means of valve 40 to source housing 42. Spark electrodes 15, the source of particles to be analyzed are located within housing 42 and suitable pumping means are connected to outlet 46 for evacuating housing 42. An ion gage 48 for measuring the pressure within the source is also provided. Electron-emitting filaments 49 are provided adjacent an exit slit 50 from the source. Filaments 49 have a dual function as heaters for the source housing and as sources of ionizing electron beams. The filaments generate electrons which bombard the slit 50 and the spark samples from electrodes raising the temperature of the interior of the source to the desired level. Free molecules from the gas supply 18 are also bombarded into ions in position to be accelerated out of the source and into the mass analyzer. A typical sample gas provided by supply 18 for calibrating and aligning the instrument is perfluorocyclobutane C F Such a gas is characterized by six major peaks from m/e 31 to m/e I31, a mass range common to spark sources. An electron bombardment source of the type described immediately above has also been found to give an energy spread similar to that obtained with spark source ions.

In operation the instrument is aligned, i.e., focused, by releasing a supply of sample gas from bottle 34 and energizing the ionizing electron beam in the source. With a supply of charged particles being directed into the analyzer the various sections can be aligned to bring the desired particles into registration at the collector.

At the same time, as sample ions are being directed through the instrument, it is calibrated, i.e., the relationship between the settings of the peak selector or peak finder (the apparatus used to generate the magnetic field and the device 26 used to control the magnitude of the field generated) and the mass in register at the collector is established. Where an electron multiplier is used as the collector, its gain is also calibrated using the known masses and quantities present in the sample gas.

As is well known, charged particles produced by a spark source have a wide energy spread and angular divergence and in order to obtain satisfactory resolution of the masses contained in the spark samples, the charged particles or ions emitted by such a source are normally subjected to both an electric and a magnetic analyzing field. Particle beams passed through both electric and magnetic fields are focused such that large angular and energy spreads are concentrated to a focal line. In the electric sector such as that shown in FIG. 1, a DC potential is imposed upon a curved sector subtending an arc of a predetermined length. Ions emerging from the electric analyzing sector then pass into a magnetic analyzing sector such as is shown in FIG. 3. Under the influence of the magnetic field created in sector 14 particles assume varying radii of curvature depending upon the mass of the particles entering the sector. Lighter masses have a more extreme curvature and heavier masses a more gradual curvature. Prior to entry into sector 14 proper particles entering the entrance end 52 of sector 14 pass total-beam-monitoring electrode 24. The output from electrode 24 is fed to a total beam monitor which includes an electrometer amplifier and an electronic integrator. Similar circuitry 30, including a collector beam monitor and integrator is connected to the output of the collector for purposes of integrating the signal transmitted from the collector. Because the charged particle beam from an electric discharge source fluctuates it has been found that it is necessary to com pensate for this phenomenon in order to obtain satisfactory accuracy in the analytical data obtained from the instrument. This is accomplished by combining the two time integrated signals from the total beam monitor and the collector in the signal comparator portion of circuitry 30 to yield a ratio which averages out the beam fluctuations thereby providing accurate quantitative data concerning the mass peak in registration at the collector.

A magnetic field control device 26 is located in the magnetic field of sector 14 and prior to an analysis device 26 is adjusted to set the analyzing magnetic field at a value which will bring a predetermined mass into registration at the entrance slit 56 to the collector. In one embodiment control device 26 is connected to the coil of an electromagnet (not shown) associated with magnetic sector 14 to control the current and the strength of the magnetic field in the sector. The manner in which the magnetic field is controlled will be discussed in more detail in conjunction with FIG. 4.

An electron multiplier 58 is provided as the charged particle collector for this particular apparatus. Charged particles entering slit 56 are communicated thereto by means of multiplier shield 60 comprising, for example, three

concentric tubes

55, 57, 59 shown in section in FIG. 3. The three concentric overlapping tubes provide a protected, gas evacuable pathway between slit 56 and multiplier 58 such that there is no line of sight path to the multiplier which would permit reflected parti-' cles outside of the protected pathway to be'transmitted to the multiplier. Shielding of the multiplier is necessary to prevent other charged particle or ion beams from being reflected into the multiplier and in preventing the multiplier from picking up stray ions. Shielding of the collector is an important aspect of the present invention and contributes significantly to the improved sensitivity obtainable with such an instrument. By reducing the background signal to a low level, fast analyses in the low parts per billion range are readily obtainable. Slit 56 is, for example, a three-way adjustable collector slit and adjustment is provided by means of lever 62; Where a photographic plate is used as the collector, inlet 64 is used as the photographic-plate-loading port. Charged particles impinging on the first dynode 66 of multiplier 58 set off an avalanche of electrons which are communicated to succeeding dynodes and from the final dynode to collector electronics (not shown) to provide a quantitative measure of the ions entering the collector slit.

Control of the magnetic field of sector 14 is accomplished in one embodiment in the manner and with the peak selector or peak finder apparatus shown in FIG. 4. As shown therein a Hall effect device 68 is located so as to be disposed in the magnetic field created in the magnetic sector of the analyzer. Device 68 may be located in the magnet gap itself or in a secondary gap between the magnet yoke and one of the pole pieces. An AC voltage source 70, a function generator, is connected by means of a matching transformer 72 through a linearizing resistor 74 to drive the Hall device. The output from the Hall device is communicated to a tuned, phase-sensitive detector 76 and to a dropping transformer 78 and a variable autotransformer 80.

Transformers

78 and 80 select a portion of the driving voltage from source 70 and add it to the output of the Hall device to cancel the zero field offset voltage of the device. A second variable autotransformer 82 and an isolation transformer 84 are also provided. Transformer 82 the background distribution in the region where peaks exist is the same as that where no peaks exist. The background distribution for the sample under analysis can be obtained either before the specific analysis for a given element is run or by making additional measurements as part of the analytical run in question. Comparison of the results of the analysis with the background distribution informs the operator whether he has detected a specific element or merely background indications. If it is determined that an element has been detected, the collector electronics also provide him with an accurate quantitative measure of the amount of the element present in the sample.

In summary, the present invention provides a mass analysis instrument capable of providing qualitative and quantitative data concerning the composition of samples, particularly solid samples with improved sensitivity when compared to mass analytical instruments previously available. This improved sensitivity is obtained while performing accurate electrical discharge trace analyses heretofore characterized by troublesome inaccuracies due to fluctuations in the charged particle beam by using a ratio of two time-integrated signals in order to correctly average out the beam fluctuations. This improvement is also due, in significant measure, to determination of the nature of the background signal normally present in such analyses and the provision of collector shielding to significantly reduce the effect of this signal. In addition, with the present invention and the utilization of a peak selector, ions of a given mass number can now be quickly collected without wasting time scanning across the entire mass spectrum.

What is claimed is:

1. A mass analyzer comprising:

a source of a sample material to be analyzed;

a first ionizing means for imparting an electrical charge to particles of the sample material;

a source of reference material separate from the source of sample material for aligning and calibrating the mass analyzer;

second ionizing means separate from said first means for imparting an electrical charge to particles of the reference material;

a magnetic analyzing sector located in the path of particles from the sample charged particle source for separating said particles according to their respective masses;

total-charged-particle-monitoring means located at an entrance end of the magnetic sector;

a collector located at an exit end of the magnetic sector;

means located in the magnetic field created for the magnetic sector for monitoring the strength of the field therein;

circuit means coupled to the monitoring means for controlling the field in the magnetic sector to bring ions of a predetermined mass into register at the collector without reference to the particles being detected at the collector; and

electrical circuit comparison means coupled to the totalcharged-particle-monitoring means and the collector for comparing the portion of the charged particle beam striking the collector with the total charged-particle beam striking the monitoring means.

2. A mass analyzer according to claim 1 wherein said first ionizing means is of the vacuum breakdown type.

3. A mass analyzer according to claim 2 wherein said first ionizing means is of the radiofrequency spark type.

4. A mass analyzer according to claim 2 wherein said first ionizing means is of the high voltage pulse type.

5. A mass analyzer according to claim 2 wherein said first ionizing means is of the high current are type.

6. The analyzer of claim 1 wherein said collector is an electron multiplier collector.

7. A double-focusing mass spectrometer comprising: a vacuum breakdown source for providing ions of a sample of a material to be analyzed: a second ion source for providing ions from a reference material;

an electric analyzing sector located adjacent said sources in position to receive ions from said sources;

a magnetic analyzing sector located at an exit end of the electric sector;

total ion beam electrode means located between the electric sector and the magnetic sector for monitoring the ion beam entering the magnetic sector;

a collector located at an exit end of the magnetic sector for monitoring the portion of the ion beam emerging from the magnetic sector;

means located in the magnetic field created for the magnetic analyzing sector for monitoring the field therein;

first electrical circuit means for changing the magnetic field in the magnetic sector by a discrete amount to a strength that will bring ions of a predetermined mass into register at the collector, said first circuit means being coupled to the magnetic field monitoring means; and

second electrical circuit means for obtaining the integral of the portion of the ion beam emerging from the magnetic sector and the integral of the total ion beam entering the magnetic sector to provide qualitative and quantitative data regarding the sample to be analyzed.

8. A mass spectrometer according to claim 7 wherein the means for monitoring the magnetic field is a magnetic field transducer utilizing a Hall effect device.

9. A mass spectrometer according to claim 8 including resistance means connected in series circuit relationship in an input circuit to the Hall effect device for linearizing the output signal from the device.

10. A mass spectrometer according to claim 7 wherein the magnetic analyzing sector includes a collector slit at the exit end thereof and shielding means comprising at least two overlapping tubes located between the collector slit and the electron multiplier collector to provide a protected pathway to the collector for ions passing through the collector slit.

11. A mass spectrometer according to claim 10 including an electrical comparison circuit for obtaining the ratio of the integral of the ion beam emerging from the magnetic sector with the integral of the ion beam entering the magnetic sector.

12. A mass spectrometer according to claim 1 1 wherein the means for monitoring the field in the magnetic analyzing sector is a Hall effect device having resistive means connected in series circuit relationship in an input circuit to said device for linearizing the output from the device.

13. A mass spectrometer according to claim 11 wherein the means for controlling the field in the magnetic analyzing sector is a magnetic field transducer utilizing a Hall effect device.

14. A mass spectrometer according to claim 1 1 wherein said second ion source is an electron bombardment type of source.

15. The spectrometer of claim 7 wherein the collector is an electron multiplier collector.

16. A double-focusing mass spectrometer comprising:

a vacuum breakdown source for providing ions of a sample of a material to be analyzed;

an electric analyzing sector located adjacent said source in position to receive ions from the source;

a magnetic analyzing sector located at an exit end of the electric sector; I

a collector located at an exit end of the magnetic sector for monitoring a portion of the ion beam emerging from the magnetic sector, said magnetic analyzing sector including a collector slit at the exit end thereof and shielding means comprising at least two overlapping tubes located between the collector slit and the collector to provide a protected pathway to the collector for ions passing through the collector slit;

first electrical circuit means for changing the magnetic field in the magnetic sector by a discrete amount to a strength that will bring ions of a predetermined mass into register selects a portion of the driving voltage from source 70 and is used as a reference adjusting transformer. The output from transformer 84 is fed to a precision variable transformer 86 and a precise fraction of this signal is then summed out of phase with the signal of the Hall device in detector 76. When detector 76, a null detector sharply tuned to the frequency of source 70, detects .a signal in phase with the signal of the Hall device 68, a signal is fed to magnet regulator 87 to decrease the current in coil 88 which controls the strength of the mag netic field in the magnetic sector. When detector 76 detects a signal which is out of phase with the output from device 68, a signal is communicated to magnet regulator 87 causing the current in coil 88 to be increased. Thus the magnetic field in the sector can be controlled by setting the ratio of transformer 86, the setting being determined by the mass peak to be brought into registration (i.e. selected) at the collector.

Transformer 86, a precision transformer, is linear to 0.000] percent and has a resolution of 0.00001 percent (0.1 p.p.m.). Such a unit is available in both manually operated and programmable versions. The programmable version is operable in responseto any of decimal, binary, or binary-coded decimal control signals. With the programmable version, the electromagnet associated with the magnetic sector is normally programmed to go through a sequence offield settings.

The analyzer of the present invention is readily adaptable to a programmed operation. As indicated previously, the precision or ratio transformer 86 is available in both manual and programmable versions. By connecting a programming system and readout means such as a printer to the analyzer and in particular including in the system means for programming transformer 86 of the peak selector apparatus, the charged particle source, the collector circuitry and the readout system, a completely automatic mass spectrometer is the result. Provision of an auxiliary gas source with the instrument for use in calibration of an analyzer utilizing a programmed magnetic field results in an analytical tool of great versatility and accuracy.

In such a programmed operation the instrument is energized and the programming system operation initiated. Thereafter the operation of the instrument is automatic and can be accomplished without attendance of an operator. This technique can be further enhanced by providing an automatic multiplesample holder for the instrument also under control of the programming system. When the several samples in the sample holder are to be analyzed the machine can be programmed to signal the operator upon completion of the various analyses required of the instrument.

In one embodiment the sequence of steps to be performed by the programming system to accomplish automatic operation include interrupting the charged particle beam and operating the readout system to print out the contents of integrating electrical circuitry connected to the collector. Thereafter the peak finder or selector apparatus is stepped to another reference level. When the printing operation if finished the printer is shifted to the next line and the integrating circuitry is reset. The charged particle beam is again turned on and the peak selector apparatus stepped from the reference level to the next peak to be detected. The printer is activated to print the peak number corresponding to the mass peak selected by the peak selector and the electrometers in the output circuit are set to the proper range. Following this step the printer is put in the no-print mode and the circuitry into the integrate mode and an analysis is run until a standard exposure (unit charge integration with time) has been accomplished. Upon completion of this step operation is recycled to perform the next analysis.

Where an automatic multiple-sample holder is used, the programming system is provided with extra logic to change samples and initiate and complete the run. in one embodiment the output of the collector is read with an autoranging digital voltmeter and a printer output. The total beam monitor 32 is provided with a full-scale indicator and upon completion of a standard exposure, that is, accumulation of a predetermined or unit amount of charge (full-scale indication) the beam monitor signals the programming system for switching from the completion of a run to the initiation of the next run. Control of the charged particle beam is accomplished by deen'ergizing the source, by energizing a deflector in the path of the beam or by switching off the signal to the integrator during the interval when it is desired that the charged particle beam not be measured.

A number of alternate embodiments are contemplated for sequencing the peak selector. In one embodiment a programming switch is provided with a plurality of contacts sufficient in number to drive the ratio transformer, to print the peak number and to sense the correct stop point on the programming switch. An added benefit of the use of such a programming switch is that the operator has a panel of yes/no switches to determine whether any given peak was to be analyzed. in another alternate embodiment the operation is accomplished with diodes and flip-flops. Still another embodiment utilizes integrated circuits.

The manner in which precise control of the magnetic field is obtained will be described in conjunction with the arrangement shown in FIG. 5, a circuit for linearizing the output of a Hall effect device. in the usual case the input resistance of a Hall device increases with the strength of the magnetic field to which it is subjected and compensation for this increase is necessary. In order to accomplish compensation the input current or the input voltage to the Hall device 68 must be monitored. However, it has been found that neither parameter alone is the correct term against which to reference the output 92 from the device. It has further been found that the linearity deviation curve of the Hall device in the current reference mode is the inverse of the deviation curve in the voltage reference mode with the exception that the deviations in the voltage mode are all larger than for comparable points in the current reference mode. By using an input reference which is primarily current but partially voltage, it has been found that it is possible to cancel such deviations and obtain accurate linearization. To this end a linearity adjust resistor 94 is provided, the resistance of which is chosen such that it is several times larger than that of the Hall device. In effect the linearity adjust resistor 94 sums the input voltage and input current signals so that the output signal from the device is proportional to the resultant summed input signals for all values of the magnetic fields to which the device is subjected.

The method of mass analysis of the present invention differs substantially from the method of analysis utilized in prior art instruments. Prior analyses typically were performed by energizing an instrument and allowing it to run for a sufficient period of time such that several photographically developable spectra of varying intensity of the elements present in the sample were recorded on the photoplate detector. When the analysis was completed the detector was removed from the instrument and developed to make the latent recordings visible for analysis by a spectroscopist. By comparing the plate with'the spectrum produced on plates bearing known spectra the user was able to determine the identity of the elements present in the sample and by utilizing instruments such as densitometers and the like, was able to determine quantitative information regarding the identified elements.

in the method of the present invention the magnetic field is adjusted to a setting corresponding to the focusing of a predetermined mass at the slit between the analyzer and the collector. This is done without knowledge as to whether such an element is present in the sample at all. The instrument is then energized and the collector electronics observed to determine whether a signal is being received at the collector. if a signal is being received at the collector, the operator knows that either the predetermined mass is present in the sample or that he is detecting a background line or spectral line of another element in the sample. This can be determined by comparison of the analysis just obtained with a study of the background distribution for the sample under analysis. As is true of the photoplate method of analysis, it is assumed that magnetic sector to provide qualitative and quantitative data regarding the sample to be analyzed. 17. The spectrometer of claim 16 wherein said collector is an electron multiplier collector.

Claims

1. A mass analyzer comprising: a source of a sample material to be analyzed; a first ionizing means for imparting an electrical charge to particles of the sample material; a source of reference material separate from the source of sample material for aligning and calibrating the mass analyzer; second ionizing means separate from said first means for imparting an electrical charge to particles of the reference material; a magnetic analyzing sector located in the path of particles from the sample charged particle source for separating said particles according to their respective masses; total-charged-particle-monitoring means located at an entrance end of the magnetic sector; a collector located at an exit end of the magnetic sector; means located in the magnetic field created for the magnetic sector for monitoring the strength of the field therein; circuit means coupled to the monitoring means for controlling the field in the magnetic sector to bring ions of a predetermined mass into register at the collector without reference to the particles being detected at the collector; and electrical circuit comparison means coupled to the totalcharged-particle-monitoring means and the collector for comparing the portion of the charged particle beam striking the collector with the total charged-particle beam striking the monitoring means.

5. A mass analyzer according to claim 2 wherein said first ionizing means is of the high current arc type.

7. A double-focusing mass spectrometer comprising: a vacuum breakdown source for providing ions of a sample of a material to be analyzed: a second ion source for providing ions from a reference material; an electric analyzing sector located adjacent said sources in position to receive ions from said sources; a magnetic analyzing sector located at an exit end of the electric sector; total ion beam electrode means located between the electric sector and the magnetic sector for monitoring the ion beam entering the magnetic sector; a collector located at an exit end of the magnetic sector for monitoring the portion of the ion beam emerging from the magnetic sector; means located in the magnetic field created for the magnetic analyzing sector for monitoring the field therein; first electrical circuit means for changing the magnetic field in the magnetic sector by a discrete amount to a strength that will bring ions of a predetermined mass into register at the collector, said first circuit means being coupled to the magnetic field monitoring means; and second electrical circuit means for obtaining the integral of the portion of the ion beam emerging from the magnetic sector and the integral of the total ion beam entering the magnetic sector to provide qualitative and quantitative data regarding the sample to be analyzed.

12. A mass spectrometer according to claim 11 wherein the means for monitoring the field in the magnetic analyzing sector is a Hall effect device having resistive means connected in series circuit relationship in an input circuit to said device for linearizing the output from the device.

14. A mass spectrometer according to claim 11 wherein said second ion source is an electron bombardment type of source.

16. A double-focusing mass spectrometer comprising: a vacuum breakdown source for providing ions of a sample of a material to be analyzed; an electric analyzing sector located adjacent said source in position to receive ions from the source; a magnetic analyzing sector located at an exit end of the electric sector; total ion beam electrode means located between the electric sector and the magnetic sector for monitoring the ion beam entering the magnetic sector; a collector located at an exit end of the magnetic sector for monitoring a portion of the ion beam emerging from the magnetic sector, said magnetic analyzing sector including a collector slit at the exit end thereof and shielding means comprising at least two overlapping tubes located between the collector slit and the collector to provide a protected pathway to the collector for ions passing through the collector slit; means located in the magnetic field created for the magnetic analyzing sector for monitoring the field therein; first electrical circuit means for changing the magnetic field in the magnetic sector by a discrete amount to a strength that will bring ions of a predetermined mass into register into the collector, said first circuit means being coupled to the magnetic field monitoring means; and second electrical circuit means for obtaining the integral of the portion of the ion beam emerging from the magnetic sector and the integral of the total ion beam entering the magnetic sector to provide qualitative and quantitative data regarding the sample to be analyzed.

17. The spectrometer of claim 16 wherein said collector is an electron multiplier collector.