US3603787A

US3603787A - Spark-type ion source and downstream deflector for mass spectrometer

Info

Publication number: US3603787A
Application number: US638857A
Authority: US
Inventors: Patrick Powers
Original assignee: Associated Electrical Industries Ltd
Current assignee: Associated Electrical Industries Ltd
Priority date: 1966-05-17
Filing date: 1967-05-16
Publication date: 1971-09-07
Anticipated expiration: 1988-09-07
Also published as: FR1523031A; GB1161431A; DE1598025A1

Abstract

In a mass spectrometer, structure is provided to improve the statistical accuracy of an analytical spectrum especially in that situation where a sample is not homogeneous. The mechanism includes one or both of: (1) structure at the ion source for moving a sample relative to another sample or an electrode of another material; and (2) structure arranged near the ion beam to deflect or suppress the ion beam.

Description

United States Patent Inventor Patrick Powers Binstead, England Appl. No. 638,857 Filed May 16,1967 Patented Sept. 7, 1971 Assignee Associated Electrical Industries Limited London, Eughnd Priority May 17, 1966, May 17, 1966 Great Britain 21825/66 and 21826/66 SPARK-TYPE ION SOURCE AND DOWNSTREAM DEFLECIOR FOR MASS SPECTROMETER 28 Claims, 6 Drawing Figs.

11.8. CI 250/4L9SA, 250/41.9 SR

Int. Cl H01 j 39/34 Field oiSearch..... 250/41.9 C,

41.9SA,41.9 SR, 41.9 SE,41.9S

[56] References Cited UNITED STATES PATENTS 2,690,521 9/1954 Turner 250/41.9 X 2,724,056 11/1955 Slepian 250/41.9 2,956,169 10/1960 King et a1 250/41.9 X 3,337,728 8/1967 Friedman et a1 250/41.9

Primary Examiner-William F. Lindquist A!t0rney-Watts, Hoffmann, Fisher and l-leinke ABSTRACT: In a mass spectrometer, structure is provided to improve the statistical accuracy of an analytical spectrum especially in that situation where a sample is not homogeneous. The mechanism includes one or both of: (1) structure at the ion source for moving a sample relative to another sample or an electrode of another material; and (2) structure arranged near the ion beam to deflect or suppress the ion beam.

PATENTEDSEP mn 3503787 SHEET 2 OF 3 3 INVENTOR.

DATEICK POM/E25 wfm ATTORNEYE SPARK-TYPE ION SOURCE AND DOWNSTREAM DEFLECTOR FOR MASS SPECTROMETER CROSS-REFERENCE TO RELATED APPLICATIONS l. "Present Simultaneous Mass Spectrometer Electrical Outputs, Ser. No. 638,287, filed May 16, 1967 by Patrick Powers.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to mass spectrometers and more particularly to a novel apparatus and method of operation of a spark-source mass spectrometer in which means is provided for movement of the sample material during analysis and in which means is provided for deflecting or suppressing an ion beam.

2. Description of the Prior Art With a spark-source mass spectrometer, a spark is drawn either between two sample electrodes or between a sample and a counter electrode of a metal such as gold to produce ions of material to be analyzed. In carrying out quantitative analysis by means of a spark-source mass spectrometer, the statistical accuracy of the results achieved have, in the past, been very closely associated with the homogeneity of the sample. This has been true because sparks have been drawn from small areas of samples and the ions to be analyzed in the mass spectrometer are derived from these small areas.

However, the distribution of impurities in many materials, which are analyzed advantageously in a spark-source mass spectrometer, is not homogeneous. For this reason, it has been difficult to analyze such materials accurately by mass spectrometry.

When using a spark-source mass spectrometer for the analysis of solids, a photographic plate is normally used as the detector of ions in the ion beam spectrum. Since the photographic plate acts as an integrating device, it records ion intensity as a density which can be independent of the variations in intensity of the ion beam which may result from irregularities of the spark.

For the purposes of quantitative analysis, a series of exposures is usually made on adjacent strips of the photographic plate, each exposure differing from the previous one by the same multiplying factor, usually a factor of 3. In order to compensate for the above-mentioned variations in intensity, exposures are usually measured in terms of the electrical charge deposited on the plate, rather than in terms of time. A typical exposure range is on the order of 0.00001-1,000 millimicrocoulombs. It is very difficult to arrange for exposures in the lower region of such a range since such small exposures require a small beam current for a short time. Also, to obtain such exposures, the conditions of the ion source must be markedly different from what they are normally.

In an attempt to overcome these difficulties, the possibility of moving the sample during analysis has been explored. Specifically, work has been carried out with moving a pointed electrode relative to a slowly translated plane coated with sample material and with moving a pointed electrode relative to a rapidly rotating plane coated with sample material. These proposals have inherent difficulties which include: (1) that of providing a sample in a plane that is uniform; (2) that of providing a plane coated with a sample without modifying the chemical or physical properties of the sample; (3) that of overcoming, with certain materials, the problem that there is little, if any, beneficial effect on the homogeneous problem; (4) that of effecting high speed revolution of a sample in a vacuum; and, (5) that of providing analytical studies of sufficient length to provide true statistical accuracy.

SUMMARY OF THE INVENTION According to one aspect of the present invention, a sparksource for a mass spectrometer is provided for producing ions of a material to be analyzed, the ions being produced by means of a plurality of spark electrodes, at least one of which comprises a sample to be analyzed. The ion source is provided with means for moving at least one of the electrodes so as to substantially continually change the position of the area on the sample from which sparks will be drawn and ions produced.

The technique of the present invention increases the area on the sample from which ions are taken, compared with known techniques of using stationary electrodes or with the point-to-plane technique. If, as usually is the case, there are two cylindrical sample electrodes arranged side-by-side, the movement may consist of rotating one or both of them about its axis, the direction and speed of rotation being chosen dependent on the sample material, the size of the exposure being made, or on the spark-source being used which, for example, may be a radio frequency or DC spark. Alternatively or additionally, the samples may be vibrated relative to one another to increase the area on the sample from which sparks are drawn and ions produced.

In cases where sample rotation is used, variation of the speed and/or direction of rotation is used to control the sensitivity of analysis when necessary. Accordingly, in one instance the two electrodes may be rotated in the same direction and in another instance they may be rotated in contrary directions. Generally, it is preferred to rotate the electrodes in a manner such that the portions on the electrodes from which sparks are drawn move toward the ion chamber exit slit of the mass spectrometer.

According to another aspect of the present invention, a means for analyzing substances by mass spectrometry is provided in which the effective exposure of an integrating ion detector is built up from one or more successive individual exposures. The succession of individual exposures is terminated when the charge accumulated on the detector has reached a predetermined value representing the effective exposure required. Preferably, the individual exposures are of equal predetermined duration and time, which must of course be short enough to provide the minimum effective exposure required with the beam at its maximum possible intensity.

Accordingly, a mass spectrometer is provided with a means for intermittently deflecting the ion beam away from an integrating ion detector. The means may comprise a slit through which the beam must pass if it is to fall on the ion detector, and accompanying means either for repeatedly sweeping the beam across the slit, preferably at a predetermined rate of deflection, or means for repeatedly switching the beam into the slit, preferably for equal predetermined periods of time. Although exposures are normally measured by determining the charge accumulated on the ion detector, it is also possible to measure them in terms of time and, with the present invention, it is contemplated that exposures may be measured by determining the number of sweeps the ion beam makes across the slit.

In order to avoid the necessity for large potentials which might be required for deflecting the ion beam in this way by means of conventional deflector slits, and thus to enable transistor circuits to be employed for this purpose, it is contemplated that a form of the invention will comprise plates extending alongside the beam path so that the beam may be deflected gradually over a considerable distance.

The invention enables short effective exposures of a photographic plate or other integrating ion detector to be achieved while a relatively intense ion beam is flowing through the mass spectrometer. Thus, the conditions in the ion source can be maintained substantially constant during a series of such exposures and analysis can be accomplished more accurately and more reproducibly. This is particularly advantageous in the analysis of aluminum and other mono-isotope materials and inhomogeneous specimens.

Accordingly, an object of the present invention is to provide a mass spectrometer with a novel apparatus and method whereby relatively inhomogeneous samples can be analyzed with greater accuracy.

An additional object of the present invention is to provide a novel method and apparatus for analyzing substances by mass spectrometry in which short exposures of the ion detector can be achieved while normal ion source conditions are maintained.

DESCRIPTION OF THE DRAWINGS FIG. 1 shows an ion source somewhat schematically and a sectional view of structure connected to the source for rotating a sample or samples;

FIG. 2 shows an ion source somewhat schematically and an elevational view with parts broken away and removed for vibrating a sample or samples;

FIG. 3 is an end elevational view seen from the left side of FIG. 2;

FIG. 4 is an exploded view of deflector plates adjacent the exit of an ion source;

FIG. 5 is a schematic view of a spark-source mass spectrometer including deflector plates and means for rotating a sample or samples; and,

FIG. 6 is a circuit diagram of the circuit which provides a pulse to one of the deflector plates.

DESCRIPTION OF THE PREFERRED EMBODIMENTS One aspect of the present invention shown in FIG. 1 generally comprises structure connected to a sample or samples for rotating them in a spark-source type mass spectrometer. An ion source is provided and designated generally by the numeral 10. The ion source 10 includes an enclosure wall 11 defining an ionization chamber 12. The rotation structure is designated generally by the numeral 14. Although only one rotation structure 14 is shown in FIG. 1, it is preferred that a second one be provided at a diametrically opposite position in the enclosure wall 11 for rotating another sample or counter electrode. Accordingly, a sample or counter electrode 18 located adjacent a sample 18 represents either a second sample of the same material as the sample 18 or may be a counter electrode such as a gold electrode. The rotation structure 14 includes a motor 15 coupled through a flexible shaft 16 to a sample drive assembly 17. As shown, the drive assembly 17 is connected to the sample 18 by intermediate members which will be described presently.

The drive assembly 17 includes a mounting flange 20 connected to the enclosure wall 11. A threaded adapter 21 is connected to the mounting flange 20 and is in turn surrounded by a tubular adjusting piece 22 to which it is threadably connected. As the adjusting piece 22 is rotated it will move translationally along its axis relative to the adapter 21. At its outer end, the adjusting piece 22 is provided with a bearing ring 24 which engages a small projection on a pressure plate 26. The pressure plate 26 does not rotate as the adjusting piece 22 is rotated, but is moved translationally with the adjusting piece 22.

An adjusting plate 30 is another portion of the drive assembly 17. The adjusting plate 30 is movable relative to the pressure plate 26 by means of

adjustment micrometers

35, 36. The adjusting plate 30 includes a tubular projection 40 which surrounds inner structure of the drive assembly 17. A bearing retention cap 42 is mounted on the end of the projection 40. The bearing retention cap 42 supports a flexible shaft retention cap 44.

A coupling drive shaft 46 is journaled in the projection 40 by bearings 47, 48. The drive shaft 46 is connected to the flexible shaft 16 by end and

spline members

49, 50, respectively. The end and

spline members

49, 50 are held in place by the shaft retention cap 44.

A drive cup 52 is mounted on the inner end of the shaft 46. The drive cup 52 carries a ring magnet 53 which forms a part ofa coupling designated generally by the numeral 54.

The ring magnet 53 surrounds another ring magnet 55 mounted on the end ofa shaft 60. THe

ring magnets

53, 55 are so arranged that rotation of the ring magnet 53 causes rotation of the ring magnet 55. The shaft 60 is journaled in a flanged mounting tube 62 and is rotatably supported on bearings 64. The bearings 64 are preferably composed of polytetrafluoroethylene, referred to hereinafter as PTFE, marketed by E. I. DuPont under the trademark TEFLON.

A flanged portion of the mounting tube 62 is connected to a bellows 65 which in turn is connected at its inner end to the mounting flange 20. A cup 66 is mounted on the other side of the flanged portion of the mounting tube 62 and a gasket 67 is interposed between them. The gasket 67 and the cup 66 are provided to seal off the ionization chamber 12 from the outer atmosphere. Cylindrical walls of the cup 66 pass between the

magnets

53, 55. The

magnets

53, 55 provide a drive coupling which, in conjunction with the cup 66 and associated structure overcomes the problem of vacuum leaks which could occur with conventional gear or direct shaft drive assemblies.

The mounting tube 62 carries a nonrotating insulating member 68 which may be moved lengthwise within the mounting flange 20 by operation of the adjustment plate 22, and fine adjustment laterally and/or lengthwise is accomplished by operation of the

adjustment micrometers

35, 36. Within the insulating member 68, the inner end of the shaft 60 is connected to a coupling member 69 which is preferably comprised of PTFE for its insulating properties. The coupling member 69 is in turn connected to a sample support shaft 72 which is journaled in ball bearings 76, 77 mounted within the insulating member 68 near its inner end. The inner end of the sample support shaft 72 is connected to a sample holder 80 which holds the sample 18.

A potential is supplied to the sample 18 through a conductor 82 connected to a carbon brush 84. The carbon brush 84 engages a tubular copper bushing 86 surrounding the shaft 72. The carbon brush 84 is biased against the copper bushing 86 by a ringlike spring 88. As shown, another sample 18, which may be a counter electrode composed of gold is mounted in a sample holder 80 connected to rotation structure (not shown) which is identical to and arranged opposite the rotation structure 14. Potential is also supplied to the sample or counter electrode 18 such that the potential difference between samples 18, 18' is, for example 80 kv. at a frequency of 500 kilocycles.

In operation, rotation is provided by the motor 15 to the drive assembly 17 in which

magnets

53, 55 coact to provide drive to the shaft 60 and ultimately to the sample 18. The sample 18 is similarly caused to rotate. Speeds of rotation are typically on the order of -600 revolutions per minute, but may be more or less if desired.

Preferably, the samples are cylindrical and are arranged side-by-side with their cylindrical surfaces adjacent one another. The desired spacing between the samples 18, 18 and suitable axial positions relative to one another may be had by appropriate adjustment of the adjusting plate 22 and/or the

adjustment micrometers

35, 36.

With the above-described sample rotation arrangement, the sensitivity of analysis may be controlled somewhat by varying the speed and/or direction of rotation of the samples 18, 18'. For example, the samples 18, 18 may be rotated in the same direction or may be rotated in opposite directions, depending upon the particular end result desired. Generally, it is preferred to rotate the samples 18, 18 in opposite directions so that the portions from which sparks are to be drawn move toward an exit slit of the ion chamber leading to the analyzer portion of a mass spectrometer.

For reasons which are explained more fully elsewhere in this specification, vibration ofa sample enhances the statistical accuracy of the results obtained with a mass spectrometer. As will be apparent to the mechanic skilled in the art, the structure thus far described may be equipped with a mechanism to vibrate the samples. However, the structure shown in FIGS. 2 and 3 is an alternative to the rotation means shown in FIG. 1. In a conventional spark-source type mass spectrometer, there is variation in a spark as it is drawn between two samples or a sample and counter electrode. The provision of relative vibration of the samples controls this variation and causes the spark to move along the sample to produce better statistical analysis of the sample.

Referring to FIGS. 2 and 3, the vibration structure comprises a vibrator motor 100 mounted on a bracket 101 and having its output connected near the middle of one portion of an elongated L-shaped plate 102. An adjusting screw 108 is provided to connect the plate 102 to the motor 100. Locking

nuts

104, 106 maintain the plate 102 in an adjusted position along the screw 108. The other portion of the plate 102 carries a pair of spaced fulcrum screws 112 and connects to a rod 115 spaced midway between the fulcrum screws 112. The fulcrum screws 112 are held in an adjusted position relative to the plate 102 by means of locking nuts 116 and shank bushings 117. The plate 102 engages the rod 115 but is permitted a certain degree of movement depending on the adjusted position of the fulcrum screws 112 which engage a plate 122 mounted on an ion source enclosure wall 11'.

A glass insulator 130, located within the ionization chamber 12', connects to the rod 115. A bellows 131 connects the rod 115 to the plate 122 permitting vibrating movement of the rod 115 and the insulator 130 relative to the enclosure wall 11'. A sample support 132 is connected at the inner end of the glass insulator 130. A sample 134 is connected to the sample support 132. The sample 134 is preferably cylindrical, but may be of another appropriate configuration.

A similar sample 135 or counter electrode is positioned, for example, substantially parallel to the sample 134. The sample 135 may be stationary or, may also be connected to identical vibration structure (not shown) arranged diametrically opposite the vibration structure shown. Wlth such an arrangement, as the samples are vibrated, the spark will be drawn from different surface portions of the samples. A vibration frequency on the order of 50-60 cycles per second has been found to be appropriate.

Another aspect of the present invention which may be used advantageously with either or both of the above-mentioned improvements generally comprises an ion beam deflection 'means 136 shown in FIG. 4. A beam deflection signal circuit 137, shown in FIG. 6, provides a deflection signal to the deflection means 136. The deflection means 136 may be positioned in the ion beam just outside the ion source, and the respective positions of the ion source and the analyzer, or analyzers if the device is to be used in a mass spectrometer employing both electrostatic and magnetic deflection, is indicated by the arrows. As shown in FIG. 5, in a double focusing mass spectrometer, an ion source 11" produces ions of material which are established by known means as an ion beam along a path. The deflection means 136 is mounted near the ion path in an ion tube 139 between the ion source 11" and the electrostatic analyzer 140, but may be positioned e1- sewhere in the instrument near the ion beam path. An ion tube, not shown, extends through an electrostatic analyzer 140 to a magnetic analyzer 142 which in turn is connected to an ion collector means 143 for receiving the ion beam to be analyzed. A suitable collector means 143 may, for example, be one of the collector arrangements disclosed in the referenced copending application of Patrick Powers.

During analysis, an ion beam, indicated by the dotted line 146, proceeds from the ion source 11" toward the analyzer 140 through a hold 150, preferably having a diameter of 0.06 inches, near the center of a circular, conductive plate 152. The plate 152 may have additional holes to accommodate additional ion beams. Spaced from the plate 152 are a pair of conductive, substantially

semicircular deflection plates

154, 155 having flange portions 158, 159 forming a gap 169 preferably of 0.125 inches between them. The plate 154 is connected to ground and the plate 155 is connected to the deflection signal circuit 137 via a conductor 161. Another circular, conductive plate 162 is spaced from and coaxial with the

plates

152, 154, 155 and has a hole 163, preferably 0.8 inches in diameter, near its center to permit the passage of the ion beam 146. The plate 162 may be provided with additional holes aligned with the gap 160 as desired.

The deflection means 136 may be assembled in a mass spectrometer by placing spacers 167 on the source side of the plate 152 and spacers 168 between the plate 152 and the deflection plate 154. The

spacers

167, 168 are preferably conductive material such as a nickel-chromium alloy which, for example, may be an item marketed by Driver-Harris Co., Harrison, New Jersey, under the name NICHROME. Spacers 169 of insulating material such as quartz are placed between the plate 152 and the deflection plate 155. Similarly, NICHROME spacers 170 are placed between the deflection plate 154 and the plate 162, and quartz spacers 171 are placed between the deflection plate 155 and the plate 162. Studs including central portions 176 and threaded end portions 178 may be inserted through the appropriate holes in the plates. Suitable nuts and washers may be fixed to the analyzer ends of the end portions 178, and the source ends of the end portions 178 may be fixed to structure within the ion tube 139. The central portions 176 are preferably composed of a silica material, for example, an item marketed by the Thermal American Fixed Quartz Co., Dover, New Jersey, under the name VITREOSIL.

The deflection signal supplied to the deflection plate 155 to cause the ion beam 146 to be deflected or suppressed is established in the deflection signal circuit 137. It is necessary to provide the deflection signal circuit 137 since ordinary commercial pulse generators will not provide a pulse, for example, on the order of +200 volts, which is required to deflect or suppress an ion beam including ions having an energy on the order of 20 kv. the deflection signal is preferably a fast square wave whose height is fixed but whose width may be varied. With a variable width pulse, the duration of intermittent ion beam exposures may be varied. In addition, means is provided so that a continuous deflection signal of constant voltage may be supplied to the deflection plate 155.

Power is supplied to the deflection signal circuit 137 from an alternating current source connected to a primary winding 186 of a transformer 187 including

secondary windings

188, 189. An output from the secondary winding 188 is applied to a full-wave rectifier bridge 190. One of the inputs of the rectifier bridge 190 is connected to the secondary winding 188 via a resistor 192. The rectifier bridge 190 has a positive output terminal 193 connected to a conductor 194 and a negative output terminal 195 connected to a conductor 196 which in turn is connected to a grounded conductor 197. The output from the secondary winding 189 is applied to a full-wave rectifier bridge 198. One of the inputs of the rectifier bridge 198 is connected to the secondary winding 189 via a resistor 199. The rectifier bridge 198 has a positive output terminal 199 connected to the conductor 197 and has a negative output terminal 200 connected to a conductor 201. The positive output terminal 199 is also connected via a conductor 202 to ground and to shielding 20 on the transformer 187.

A portion of the deflection signal circuit 137 connected across the rectifier bridge 190 includes a pair of

filer capacitors

205, 206, connected in parallel across the

conductors

194, 197. A resistor 208 is interposed in the conductor 194 between the connections for the

filter capacitors

205, 206. Three Zener diodes 210, 21 1, 212, provided to protect against surges, are connected in series across the

conductors

194, 197. A stabilized positive supply voltage of +250 volts with respect to ground appears across the Zener diodes 210-212.

A portion of the deflection on circuit connected across the rectifier bridge 198 includes a filter capacitor 215 connected across the

conductors

197, 201. A Zener diode 219 is also connected across the

conductors

197, 201 to protect against surges. A resistor 220 is interposed in the conductor 201 between the connections for the filter capacitor 215 and the Zener diode 219. A stabilized negative supply voltage of -12 volts, fi percent, appears across the Zener diode 219.

The deflection signal circuit 137 includes a high speed driver stage 230 for providing an output to an amplifier 232, which may be referred to as a beanstalk amplifier, which in turn delivers an output pulse to a conductor 234. The output appearing on the conductor 234 is fed to the conductor 161 connected to the deflection plate 155.

An input pulse is provided to the deflection signal circuit 137 along a conductor 236 via a contact C1 of a reed relay 238 shown in its normally deenergized condition in FIG. 6. The input pulse appearing on the conductor 236 may be provided by an ordinary pulse generator which, for example, may be a Rutherford type CMCB14, a Data Pulse Model 100, or any other pulse generator which will provide a variable width pulse of negative 14 volts with respect to ground with a rise time of less than 30 microseconds.

The input pulse appearing on the conductor 236 is fed via contact C1 to the high speed driver stage 230 via a conductor 240. The conductor 240 is connected via a resistor 242 to base 244 of a PNP transistor 246, on the one hand, and is connected via a resistor 248 to base 250 of an NPN transistor 252, on the other hand. Emitter 256 of the transistor 246 is connected to the conductor 197, and the base 244 of the transistor 246 is connected to the conductor 197 via a diode 254. Emitter 260 of the transistor 252 is connected to the conductor 201, and the base 250 of the transistor 252 is connected to the conductor 201 via a diode 258. The

diodes

254, 258 are fast switching diodes to provide overvoltage protection between the base and emitter elements of the associated transistors. Collector 262 of the transistor 246 is connected to collector 264 of the transistor 252 and a conductor 266 via

diodes

267, 268, 269, and 270.

An output from the driver stage 230 is fed to the amplifier 232 via the conductor 266 connected to base 282 of an NPN transistor 284. A diode 286 is connected across the base 282 and emitter 288 of the transistor 284. The diode 286 is a fast switching diode to provide overvoltage protection between the base 282 and the emitter 288. Collector 290 of the transistor 284 is connected to emitter 292 of an NPN transistor 294 via a conductor 296. The emitter 288 of the transistor 284 is connected to base 298 of the transistor 294 via a conductor 300 including a resistor 302. The emitter 288 is also connected to the conductor 201 via a resistor 303. A diode 304 is connected across the conductors 296, 300. The diode 304 is a fast switching diode to provide overvoltage protection between the base 298 and the emitter 292 of the transistor 294. The base 298 is connected via the conductor 300 and a resistor 306 to a point on the conductor 194 between two

resistors

308, 310. The resistor 308 is a load resistance and the resistor 310 is provided to insure adequate base drive current to the transistor 294 in its on condition. Collector 312 of the transistor 294 is connected to the cathode element of a diode 314 in conductor 197 and to the cathode element of a diode 314 in conductor 194. The diodes 312, 3. The may be termed catching diodes" vibrated insure that the output pulse appearing on conductor 234 will fall to zero within plus or minus 0.2 volts. This range is especially important, since the ion beam 146 is switched on when the signal appearing on the conductor 234 is in the zero voltage condition.

In operation, an input pulse is provided to the deflection signal circuit 137 on the conductor 236 from a pulse generator of the type described. When the input pulse from the pulse generator is at zero volts, the transistor 246 is turned off; the transistor 252 is turned on; the transistors 284, 294 are turned off; and, the output voltage appearing on the conductor 234 is a positive 200 volts. When the output from the pulse generator is at a negative 14 volts, the transistor 246 is turned on; the transistor 252 is turned off; the transistors 284, 294 are turned on; and, the output voltage output on the conductor 234 is zero volts, with respect to ground, plus or minus 0.2 volts.

The output pulse appearing at the conductor 234 during such operation may be further described as being a square wave having a height of plus 200 volts with respect to ground, having rise and fall times of less than 200 nanoseconds, and having a variable width of not more than 400 nanoseconds longer than the input pulse appearing on the conductor 236 from the pulse generator. It should be understood that during periods when the deflection signal is at a positive 200 volts, the ion beam 146 will be deflected toward the ground plate 154 and in effect, suppressed.

The ion beam 146 may be deflected or suppressed for longer periods of time by providing a suitable supply signal, which may be referred to as a condition" signal, along a conductor 320 including a resistor 322 connected to the relay 238, which is preferably a reed relay. A suitable supply would produce a signal of 15 volts and 20 milliamperes, which supply may be connected to the conductor 320 for as long a period as desired to deflect or suppress the ion beam 146. When the condition" signal is applied to the conductor 320, the relay 238 is energized causing a transfer to relay contact C2 resulting in the base 244 of the transistor 246 being connected to ground through the resistor 242. This turns the transistor 246 off. in this condition, the transistor 252 is on; the transistors 284, 294 are off; and, a positive signal of approximately 200 volts appears on the conductor 234 to deflect or suppress the ion beam 146. It should be understood that as long as the condition" signal is applied to the conductor 320, that a positive output voltage of approximately 200 volts will appear on the conductor 304 to deflect or suppress the ion beam 146.

In one mode of operation, the ion beam 146 may be normally deflected onto the grounded deflection plate 154 by applying the condition" signal to the conductor 320. When the spark between the samples has reached its operating level, the condition pulse may be tenninated, causing a transfer to relay contact C1 to produce a pulsed deflection signal on the conductor 234. The pulsed deflection signal will intermittently or periodically deflect the ion beam onto the deflection plate 154 and switch the ion beam 146 into a path between the gap 160 and through the hole 163 to be ultimately collected. Thus, for effecting a succession of individual exposures on the collecting means 143, the deflection plate 155 is repeatedly and rapidly brought from its normally positive potential condition to zero potential and back again to its normally positive condition of the same polarity. Thus the ion beam 14 is always deflected in the same direction away from its path toward collecting means 143.

Alternatively, the deflection plate 155 could be made alternately positive and negative with respect to ground as by applying a sine-wave or other suitably shaped alternating potential to it. With such a signal, the ion beam would be swept across the gap and through the hole 163 in both directions.

For terminating a succession of individual exposures when the charge laid down on the ion detector or collector means has reached a predetermined value representing the effective exposure required, an auxiliary ion collector 145, as shown in FIG. 5, may be provided in front of the collector means 143 (that is, between it and the last analyzer stage of the spectrometer). The auxiliary ion collector 145 has a slit through which about half of the ions will pass to the collector means 143 when the beam is in focus. The other half will impinge on the auxiliary collector 145, and the latter is connected to a capacitive storage circuit C which acts as an integrator of the beam current and is arranged automatically to terminate the succession of exposures, for example, by operating the relay 238, when a predetermined quantum of ions has been collected and a corresponding quantum of ions has passed to the collector means 143. Systematic errors which might otherwise result in inaccurate exposures, such as fluctuations in supply voltage or variations in the spark, can thus be avoided. it should also be recalled that deflection of the ion beam 146 is accomplished while maintaining relatively constant conditions in the ion source 11" thereby further enhancing the accuracy of analysis.

Many modifications and variations of the invention will be apparent to those skilled in the art in view of the foregoing detailed disclosure. Therefore, it is to be understood that, within the scope of the appended claims, the invention can be practiced otherwise than as specifically shown and described.

What is claimed is:

1. A mass spectrometer for analyzing material comprising:

a. a spark-type ion source including first and second means to mount a pair of electrodes, at least one of which is a sample electrode, in spaced relationship and means for drawing a spark between the electrodes for producing ions of a material to by analyzed, the ions being established as an ion beam along a path;

. one of the mounting means including means for rotating the sample electrode;

. the first mounting means including means for vibrating its supported electrode relative to the other electrode while maintaining the two in spaced relationship;

. a magnetic analyzer disposed along the ion beam path;

. collector means disposed in the ion beam path for receiving ions to be analyzed; and deflection means disposed adjacent the ion beam path for deflecting the ion beam so as to interrupt exposure of the ion beam on said collector means.

2. The apparatus of claim 1 wherein a deflection signal circuit for producing a pulsed deflection signal is connected to the deflection means.

3. The mass spectrometer of claim 1 wherein the vibrated electrode is a sample.

4. The mass spectrometer of claim 1 wherein both electrodes are rotated.

5. A mass spectrometer for analyzing material comprising:

a. a pair of electrodes, at least one of which is a cylindrical sample electrode, said electrodes being generally parallel and in side-by-side relation;

b. a spark-type ion source including means to mount the electrodes in spaced relationship and draw a spark therebetween to produce ions of a material to be analyzed, the source also including means to establish the ions as an ion beam along a path;

c. the one of the mounting means supporting the sample electrode including means for rotating the sample electrode to increase the area of the sample from which the spark is drawn by drawing the spark over the annular surface portion of the specimen while restraining the sample electrode to prevent movement along its axis;

d. a magnetic analyzer disposed along the ion beam path;

and,

e. collector means disposed in the ion beam path for receiving ions to be analyzed.

6. The mass spectrometer of claim 5 wherein each mounting means includes means for rotating its supported electrode.

7. The mass spectrometer of claim 6, wherein the means for rotating the supported electrodes rotate the electrodes in opposite directions such that the portions of the electrodes from which a spark is drawn move toward an ion chamber exit in the direction of ion beam travel.

8. A mass spectrometer for analyzing material comprising:

b. a spark-typeion source including means to mount the electrodes in spaced relationship and draw a spark therebetween to produce ions of a material to be analyzed, the source also including means to establish the ions as an ion beam along a path;

. one of the mounting means including means to vibrate its supported electrode substantially constantly to increase the area of the sample from which the spark is drawn by drawing the spark over the surface of the sample of electrode as a spark is drawn toward and away from the other electrode while maintaining the electrodes in spaced relationship;

d. a magnetic analyzer disposed along the ion beam path;

and,

9. The mass spectrometer of claim 8 wherein each of the mounting means includes means to vibrate its supported electrode while maintaining the electrodes in spaced relationship.

10. The method of analyzing material in a mass spectrometer comprising the steps of:

ill

a. producing ions of the material to be analyzed by drawing; a spark between first and second electrodes one of which. is a sample electrode; b. rotating the sample electrode as the spark is being drawn; c. vibrating at least the first electrode as the spark is being.

drawn while maintaining the electrodes in spaced relationship;

d. establishing the ions in an ion beam;

e. deflecting the ion beam with a magnetic analyzer; and,

f. collecting the ion beam on a collector and intermittently interrupting the collection of the ion beam on the collector by deflecting the ion beam.

11. The method of claim 10 wherein intermittently deflecting the ion beam is accomplished by applying a pulsed deflec- 1 tion signal to deflection plates arranged near the ion beam.

12. The method of analyzing the material in a mass spectrometer comprising the steps of:

a. producing ions of the material to be analyzed by drawing a spark between electrodes, at least one of which is a sample, said electrodes being generally parallel and in sideby-side relation;

b. vibrating at least one electrode during the period of the spark while maintaining the electrodes spaced, thereby increasing the area of the sample from which the spark is drawn by moving the spark along the electrodes to produce ions from a relatively large sample surface area;

c. establishing the ions in an ion beam;

d. deflecting the ion beam with a magnetic analyzer; and,

e. collecting the ion beam on a collector.

13. The method of claim 12 wherein both electrodes are vibrated as they are maintained in spaced relationship.

14. The method of analyzing material in a mass spectrometer comprising the steps of:

a. producing ions of the material to be analyzed by drawing a spark between electrodes, at least one of which is a sample electrode, said electrodes being generally parallel and in side-by-side relation; and,

b. distributing the ion production over an annular surface of the sample electrode thereby increasing the area of the sample from which the spark is drawn by rotating the sample electrode as the spark is being drawn. while restraining the sample electrode to prevent movement along its axis.

15. The method of claim 14, wherein both electrodes are rotated simultaneously.

16. The method of claim 15, wherein the electrodes are rotated in opposite directions such that portions of the electrodes from which a spark is drawn are moved toward the path of ion travel.

17. A method of analyzing material in a mass spectrometer comprising the steps of:

a. producing ions of the material to be analyzed by drawing a spark between electrodes at least one of which is a sample;

b. establishing the ions in an ion beam;

c. deflecting the ion beam with a magnetic analyzer;

d. collecting the ion beam on a collector; and,

e. extending the time over which ions are collected and thereby obtaining a more reliable spectra of the sample by intermittently interrupting the collection of the ion beam on the collector by deflecting the ion beam.

18. The method of claim 17, wherein intermittently deflecting the ion beam is accomplished by applying a pulsed deflection signal to deflection plates arranged near the ion beam.

19. The method of analyzing the material in a mass spectrometer comprising the steps of: I

a. producing ions of the material to be analyzed by drawing a spark between electrodes, at least one of which is a sample;

b. vibrating at least one electrode during the period of the spark while maintaining the electrodes spaced, thereby moving the spark along the electrodes to produce ions from a relatively large sample surface area;

c. establishing the ions in an ion beam;

d. deflecting the ion beam with a magnetic analyzer;

e. collecting the ion beam on a collector; and,

f. intermittently deflecting the ion beam so as to interrupt collecting the ion beam on the collector means.

20. In a mass spectrometer having an ion source, a collector, structure establishing a path of travel of an ion beam from said ion source to said collector, and an analyzer along said path of travel for deflecting said beam and focusing portions of said beam onto said collector, the improvement comprising:

a. deflection means disposed adjacent said path of travel for deflecting said ion beam; and

b. energizing means for energizing said deflection means with signals of predetermined width to interrupt focusing of said beam on said collector cyclically during analysis of a given sample to increase reliability of said analysis.

21. The improvement of claim 20, wherein said width is variable.

22. The improvement of claim 20, wherein said deflection means comprises a pair of spaced apart conductive plates defining a gap through which said ion beam passes when said deflection means are unenergized 23. The improvement of claim 22, wherein one of said plates is maintained at a constant potential and the other of said plates is connected to said energizing means.

24. The improvement of claim 23, wherein said constant potential is ground potential.

25. The improvement of claim 24, wherein said energizing means provides positive signals to prevent said ion beam from passing through said gap. I

26. The improvement of claim 25, wherein said width is variable.

27. A method of analyzing material in a mass spectrometer, which material may have impurities therein, comprising the steps of:

a. producing ions of the material to be analyzed;

b. establishing the ions in an ion beam;

c. deflecting the beam with an analyzer;

d. collecting the ion beam on a collector; and

e. extending the time over which ions are collected and thereby reducing the effect of said impurities to obtain a more reliable spectra of said material by interrupting collection of said beam on said collector by cyclically deflecting said ion beam away from said collector during analysis of said material.

28. The method of claim 27, wherein the collection of the beam is interrupted by providing a substantially square wave of variable width to deflect said beam.

Column Column Column Column Column subst Column Coltunn Column Column Column Column Column (SEAL) Attes't:

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 0 7527 Dated September- 1 197 Invent0r(s) Patrick Powers 6, line itute 6, line line line

line

, line line , line It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

substitute 160 after "output terminal" delete "199",

delete "199", substitute 199a after "shielding" delete "20", substitute delete "filer", substitute filter delete "on substitute signal delete "3. The", substitute 314,

delete "vibrated" substitute to delete "l4", substitute 146 Signed and sealed this 18th day of April 1972.

EDWARD M.FLETCHJ:JR,JR. Attestinrr Officer ROBERT GOTTSCHALK RM PO 1OSO(10-69) USCOMM-DC 603764- 59 w u s, GDVERNMENY Pnm'rmc OFFICE 1909 O-JGl-JJI

Claims

1. A mass spectrometer for analyzing material comprising: a. a spark-type ion source including first and second means to mount a pair of electrodes, at least one of which is a sample electrode, in spaced relationship and means for drawing a spark between the electrodes for producing ions of a material to by analyzed, the ions being established as an ion beam along a path; b. one of the mounting means including means for rotating the sample electrode; c. the first mounting means including means for vibrating its supported electrode relative to the other electrode while maintaining the two in spaced relationship; d. a magnetic analyzer disposed along the ion beam path; e. collector means disposed in the ion beam path for receiving ions to be analyzed; and f. deflection means disposed adjacent the ion beam path for deflecting the ion beam so as to interrupt exposure of the ion beam on said collector means.

3. The mass spectrometer of claim 1 wherein the vibrated electrode is a sample.

4. The mass spectrometer of claim 1 wherein both electrodes are rotated.

5. A mass spectrometer for analyzing material comprising: a. a pair of electrodes, at least one of which is a cylindrical sample electrode, said electrodes being generally parallel and in side-by-Side relation; b. a spark-type ion source including means to mount the electrodes in spaced relationship and draw a spark therebetween to produce ions of a material to be analyzed, the source also including means to establish the ions as an ion beam along a path; c. the one of the mounting means supporting the sample electrode including means for rotating the sample electrode to increase the area of the sample from which the spark is drawn by drawing the spark over the annular surface portion of the specimen while restraining the sample electrode to prevent movement along its axis; d. a magnetic analyzer disposed along the ion beam path; and, e. collector means disposed in the ion beam path for receiving ions to be analyzed.

8. A mass spectrometer for analyzing material comprising: a. a pair of electrodes, at least one of which is a cylindrical sample electrode, said electrodes being generally parallel and in side-by-side relation; b. a spark-type ion source including means to mount the electrodes in spaced relationship and draw a spark therebetween to produce ions of a material to be analyzed, the source also including means to establish the ions as an ion beam along a path; c. one of the mounting means including means to vibrate its supported electrode substantially constantly to increase the area of the sample from which the spark is drawn by drawing the spark over the surface of the sample of electrode as a spark is drawn toward and away from the other electrode while maintaining the electrodes in spaced relationship; d. a magnetic analyzer disposed along the ion beam path; and, e. collector means disposed in the ion beam path for receiving ions to be analyzed.

10. The method of analyzing material in a mass spectrometer comprising the steps of: a. producing ions of the material to be analyzed by drawing a spark between first and second electrodes one of which is a sample electrode; b. rotating the sample electrode as the spark is being drawn; c. vibrating at least the first electrode as the spark is being drawn while maintaining the electrodes in spaced relationship; d. establishing the ions in an ion beam; e. deflecting the ion beam with a magnetic analyzer; and, f. collecting the ion beam on a collector and intermittently interrupting the collection of the ion beam on the collector by deflecting the ion beam.

11. The method of claim 10 wherein intermittently deflecting the ion beam is accomplished by applying a pulsed deflection signal to deflection plates arranged near the ion beam.

12. The method of analyzing the material in a mass spectrometer comprising the steps of: a. producing ions of the material to be analyzed by drawing a spark between electrodes, at least one of which is a sample, said electrodes being generally parallel and in side-by-side relation; b. vibrating at least one electrode during the period of the spark while maintaining the electrodes spaced, thereby increasing the area of the sample from which the spark is drawn by moving the spark along the electrodes to produce ions from a relatively large sample surface area; c. establishing the ions in an ion beam; d. deflecting the ion beam with a magnetic analyzer; and, e. collecting the ion beam on a collector.

13. The method of claim 12 wherein both electrodes are vibrated as they are maintained in spaced relationship. 14. The method of analyzing material in a mass spectrometer comprising the steps of: a. producing ions of the material to be analyzed by drawing a spark between electrodes, at least one of which is a sample electrode, said electrodes being generally parallel and in side-by-side relation; and, b. distributing the ion production over an annular surface of the sample electrode thereby increasing the area of the sample from which the spark is drawn by rotating the sample electrode as the spark is being drawn while restraining the sample electrode to prevent movement along its axis.

15. The method of claim 14, wherein both electrodes are rotated simultaneously.

17. A method of analyzing material in a mass spectrometer comprising the steps of: a. producing ions of the material to be analyzed by drawing a spark between electrodes at least one of which is a sample; b. establishing the ions in an ion beam; c. deflecting the ion beam with a magnetic analyzer; d. collecting the ion beam on a collector; and, e. extending the time over which ions are collected and thereby obtaining a more reliable spectra of the sample by intermittently interrupting the collection of the ion beam on the collector by deflecting the ion beam.

19. The method of analyzing the material in a mass spectrometer comprising the steps of: a. producing ions of the material to be analyzed by drawing a spark between electrodes, at least one of which is a sample; b. vibrating at least one electrode during the period of the spark while maintaining the electrodes spaced, thereby moving the spark along the electrodes to produce ions from a relatively large sample surface area; c. establishing the ions in an ion beam; d. deflecting the ion beam with a magnetic analyzer; e. collecting the ion beam on a collector; and, f. intermittently deflecting the ion beam so as to interrupt collecting the ion beam on the collector means.

20. In a mass spectrometer having an ion source, a collector, structure establishing a path of travel of an ion beam from said ion source to said collector, and an analyzer along said path of travel for deflecting said beam and focusing portions of said beam onto said collector, the improvement comprising: a. deflection means disposed adjacent said path of travel for deflecting said ion beam; and b. energizing means for energizing said deflection means with signals of predetermined width to interrupt focusing of said beam on said collector cyclically during analysis of a given sample to increase reliability of said analysis.

21. The improvement of claim 20, wherein said width is variable.

22. The improvement of claim 20, wherein said deflection means comprises a pair of spaced apart conductive plates defining a gap through which said ion beam passes when said deflection means are unenergized

23. The improvement of claim 22, wherein one of said plates is maintained at a constant potential and the other of said plates is connected to said energizing means.

25. The improvement of claim 24, wherein said energizing means provides positive signals to prevent said ion beam from passing through said gap.

26. The improvement of claim 25, wherein said width is variable.

27. A method of analyzing material in a mass spectrometer, which material may have impurities therein, comprising the steps of: a. producing ions of the material to be analyzed; b. establishing the ions in an ion beam; c. deflecting the beam with an analyzer; d. colLecting the ion beam on a collector; and e. extending the time over which ions are collected and thereby reducing the effect of said impurities to obtain a more reliable spectra of said material by interrupting collection of said beam on said collector by cyclically deflecting said ion beam away from said collector during analysis of said material.