Spark Source Mass Spectrometers And Sample Insertion Probe Therefor

Abstract

A mass spectrometer with an insertion probe for holding and inserting a sample through a vacuum lock. Means are provided for cleaning the samples.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

1. Application Ser. No. 460,392, entitled "Mass Spectrometer sealed Vacuum Lock," now U.S. Pat. No. 3,440,417, issued Apr. 22, 1969 invented by John Stewart Heath.

BACKGROUND OF INVENTION

1. Field of the Invention

The invention relates to ionization sources for mass spectrometers and more particularly to a novel insertion probe, novel cooperating structure for causing ionization of material, and to a novel method of operating a mass spectrometer.

2. Description of the Prior Art

In mass spectrometers of the type in which ionization is accomplished with an electron beam, devices have existed for introducing samples into an ion source chamber for analysis without destroying the vacuum in the ionization chamber. Thus, the desirability of causing as little disturbance as possible to the high vacuum existing within the ion chamber has been recognized. One system for maintaining vacuum in an electron beam type mass spectrometer is described and claimed in U.S. Pat. No. 3,158,740 issued Nov. 24, 1964 to R. D. Craig et al. under the title Mass Spectrometer Sample Insertion Devices. While the problems attendant to destroying the source vacuum have been met and solved Sealed mass spectrometers with electron beam sources, with prior spark-type ion sources, when the solid sample is placed in an ion source chamber, the chamber is opened to the atmosphere and air is permitted to enter the chamber.

When a chamber is opened to the atmosphere, in addition to the relatively apparent problem of destroying the existing vacuum, other undesirable conditions are produced within the chamber. One undesirable condition is that contaminating molecules of such materials as certain gases and water become attached to the surfaces within the chamber by a process known as adsorption. When the vacuum is reestablished, these contaminating molecules are released to a certain extent and limit the vacuum that can thereafter be attained. Removal of these contaminating molecules and consequent reduction in their partial pressure can be achieved only by pumping for long periods or by raising the temperature of the chamber enclosure.

A reduction in the partial pressure of the contaminating molecules of foreign matter has been found to be necessary for at least two reasons. First, it is necessary to have a low partial pressure of residual gases in the analyzer portion of the mass spectrometer to permit the unobstructed passage of ions without collision with gaseous contaminating foreign molecules. These collisions are undesirable since they tend to scatter the ions and thus reduce the resolving power and accuracy of the instrument. Second, a low partial pressure of contaminating foreign molecules of oxygen and water vapor is necessary in the ion source chamber in order that ions of oxygen originating from the sample material will not be masked by ions of oxygen originating from stray molecules of residual foreign gases. It is often desirable to detect small traces of oxygen in solid material since it is known that the properties of many materials are sensitive to concentrations of oxygen of less than one part in one million.

Another problem with prior mass spectrometers is that the solid samples often become contaminated before being introduced into the ion source chamber. Normally, decontamination of the surfaces of the samples is carried out in a separate vacuum vessel and during transfer from the vacuum vessel to the ion source chamber the samples are often unavoidably contaminated both through handling and by the reformation of surface oxide layers resulting from contact with atmospheric oxygen.

SUMMARY OF THE INVENTION

With the present invention, a mass spectrometer has the usual evacuable ionization chamber. A probe is provided for introducing a sample or samples for analysis into the evacuated chamber. Samples are introduced through a vacuum lock which permits insertion of the probe while maintaining a high vacuum within the ionization chamber. The probe positions each sample selectively and one at a time at cleaning and analyzing positions within the chamber.

As will become more apparent, the probe can be used to insert either one sample or a pair of samples simultaneously. For purposes of explanation, the use of two samples will be discussed, yet it should be understood that a single sample can be used. This permits use of the known techniques of either (1) establishing an arc between two samples of the same material or, (2) when desired, as when arcing is difficult because the sample is a crystal or the like, using a counter electrode of gold or other relatively stable metal material and a single sample.

A cleaning electrode is mounted within the chamber for use when the samples are mounted on the probe in its cleaning position. The cleaning electrode is about the samples so that the samples may be etched and thereby cleaned by ion bombardment. There is also an access to the chamber for introducing a continuous flow of an inert gas into the chamber during the etching of the samples and for removing the gas and evacuating the chamber subsequent to etching and prior to ionization of the samples.

After the samples have been cleaned, the probe is movable to the analyzing position. There the samples are positioned in electrode supports at which time the samples are in their analyzing position. After the probe has positioned the samples in their analyzing positions the probe is removed and a spark may be drawn between the sample and a counter electrode or between the samples to ionize the sample material. Alternatively, a laser generator mounted externally of the chamber may be used to ionize the sample material in which case the probe need not position the samples in the electrode nor does it need to be withdrawn.

The above-referenced U.S. Pat. No. 3,440,417 discloses an insertion lock including a plug for opening and closing a passageway and for providing communication via this passageway between an exhaust port and an ion source chamber. An insertion probe can be moved axially in the passageway to introduce the sample into the chamber.

With the insertion probe bearing a sample initially placed in the passageway, the valve may be opened and a vacuum maintained within the chamber since the probe seals off the passageway. After the sample has been positioned in the chamber, the probe may be withdrawn past the plug but yet sealing off the passageway. After the plug is closed, the probe may be fully withdrawn from the passageway without materially affecting the vacuum in the chamber.

In one form of the invention, the insertion probe includes a tube having a plate connected at one end. The plate is connected to the inner sides of the tube so as to be aligned with the central axis of the tube and extends outwardly from the end of the tube. A control rod extends through the length of the tube and has a pistonlike sealing member connected at the end of the control rod adjacent the plate forming a fluidtight seal with the inner surface of the tube. A pair of sample positioners are connected to the pistonlike sealing member. The positioners are arranged in staggered fashion on opposite sides of the plate and extending outwardly from the tube opening parallel to the axis of the tube. A pair of pins are mounted in staggered fashion on opposite sides of the plate adjacent and on opposite sides of the sample positioners. Each sample holder has a slot in its side. The pins are each disposed in an associated one of the slots with the slots facing in opposite directions away from the adjacent and associated one of the sample positioners. Samples are mounted on the ends of the sample holders which ends are the ends furthest from the tube.

At the end of the control rod remote from the samples, a portion of the control rod extends from the tube so that the rod may be rotated manually or otherwise. The tube has a control slot formed near this end of the tube and a key connected to the control rod is adapted to travel in the control slot for guiding the movement of the sample positioners. The control slot has a portion aligned parallel to the axis of the tube, a second portion aligned somewhat transverse to the axis, and another portion aligned parallel to the axis of the tube and extending in an opposite direction from the other parallel portion.

In the form of the invention wherein the sample is ionized by a laser beam, the sample remains mounted at the end of the insertion probe and the laser beam originates from a laser generator external of the ionization chamber.

Accordingly, the principal objects of the present invention are to provide a novel and improved mass spectrometer including structure for maintaining a vacuum in the source when a sample is inserted, novel structure for cleaning a sample in an evacuated chamber, a novel sample insertion device, and a novel method of operating a mass spectrometer.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a novel spark-type ion source in cross section;

FIG. 2 is a detailed view of the end of the insertion probe for holding the samples;

FIG. 3 is a view of the right side of the end of the insertion probe shown in FIG. 2;

FIG. 4 is a view of a sample holder in rotated position and an accompanying sample positioner; and,

FIG. 5 is a cross-sectional view of an alternative form of the novel ion source with laser ionization.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, an ion source is shown generally at 10. The ion source 10 has an enclosure wall 14 which defines an ionization chamber 16. An insertion lock 12 is connected to the enclosure wall 14. The insertion lock 12 is provided with a passage 17 which communicates with the ionization chamber 16. An insertion probe 18 is shown inserted in the passage 17 in slidable engagement with the interior members of the insertion lock 12.

The ion source 10 includes movable mountings 19, 20 in the form of bellows secured to openings on opposite sides of the enclosure wall 14. A pair of insulating supports 26, 28 composed of an insulating material are connected to the movable mountings 19, 20 respectively and are located within the ionization chamber 16. The insulating supports 26, 28 are respectively connected to a pair of manipulators 22, 24 located outside the ionization chamber 16 and to a pair of slotted electrode mounts 30, 32 composed of electrically conductive material located opposite one another within the ionization chamber 16.

A source terminal mounting 34 composed of insulating material is mounted in an aperture in the enclosure wall 14. A pair of source terminals 36, 38 project through the mounting 34 and are adapted to be connected to an external high-voltage source. A pair of source leads 40, 42 are connected between interior ends of the source terminals 36, 38 respectively and to the electrode mounts 30, 32 respectively to provide high voltage to the electrode mounts 30, 32 for establishing an ionizing spark when samples are carried by them.

A cleaning electrode terminal mounting 44 composed of insulating material projects through an aperture in the enclosure wall 14 near the passage 17. A cleaning electrode terminal 46 projects through the cleaning electrode mounting 44 into the chamber 16. A lead 48 for supplying a high-positive potential is connected to the outer end of the electrode terminal 46 and a cleaning electrode 50 is mounted on the opposite end of the electrode terminal 46 within the ionization chamber 16 adjacent the inner end of the passage 17. The cleaning electrode 50 is preferably annular and has its center aligned along the longitudinal axis of the passage 17 for at least partially surrounding a sample or samples inserted in the chamber and thereby permitting a uniformly cleaned sample to be obtained. Cleaning is accomplished by applying 2kv. to the electrode 50 in the presence of argon so that a sample surface is bombarded by argon ions which removes surface atoms.

The insertion lock 12 includes a body 52, an end block 54 connected at the outer end of the body 52, and a flanged, tubular mounting member 56 connected to the inner end of the body 52. The mounting member 56 is connected to the enclosure wall 14. The passage 17 extends through the end block 54, the body 52, and the mounting member 56 and is defined by the inner structure of the insertion lock 12.

A pair of tubes 59, 61 are connected to the side of the body 52 and define ports 60, 62 respectively, each of which communicates with the passage 17. The tubes 59, 61 may be connected to vacuum pumps. A valve plug 64 is located within the passage 17 and is preferably in the form of a rotary ball. A valve shaft 66 is positioned radially outwardly from the passage 17, and is connected to the valve plug 64. The shaft 66 passes through a mounting cup 68 which carries seal structure to be described presently. On its opposite side, the plug 64 engages an annular bearing end seal 70.

The plug 64 has a bore 72 which, in the open position shown in FIG. 1, communicates with and forms a part of the passage 17. The plug 64 has a transverse bore 74 connecting the port 62 to the bore 72 to provide a path for withdrawing gases through the passage 17.

The insertion lock 12 includes a number of seals some of which are constructed to slidably engage the outer surface of the insertion probe 18 so that a high vacuum can be maintained in the ionization chamber 16 while the insertion probe seals off the passage 17.

The plug 64 is clamped between two plug seals 76, 78 each of which is provided with an opening for admitting the insertion probe 18. The plug seal 78 engages a seal wedge 80 at the side of the plug 64 toward the chamber 16. A disc spring 82 located between the mounting member 56 and the seal wedge 80 biases the seal wedge 80 against the plug seal 78. This biases the plug seal 78 against the inner walls of the body 52 and against the plug 64. Another plug seal 84 surrounds the shaft 66 and engages the shaft side of the plug 64. A seal wedge 86 is biased against the plug seal 84 by a disc spring 88 located between the seal wedge 86 and the cup 68. This biases the plug seal 84 against the inner walls of the body 52 and against the plug 64.

A sliding seal 102 including a flange 103 is positioned near the outer end of the passage 17 and around the insertion probe 18. The sliding seal may be formed of Polytetrafluoroethylene sold under the trademark "Flourosint" by Polypenco Limited, Welwyn Garden City, Herts, England. The sliding seal 102 has radially extending flange 103 which abuts the inner end of the block 54. The sliding seal 102 is identified as a sliding seal because, while it remains stationary relative to the insertion lock 12, it provides a seal against the outer surface of the insertion probe 18 as it is shifted axially in the passage 17. This permits a vacuum to be maintained in the ionization chamber 16 and only the insertion probe 12 blocking the passage 17.

An annular seal wedge 100 is positioned next to the sliding seal 102 and a seal wedge 96 engages the seal wedge 100. A spacing tube 92 is provided which has an opening 75 at one side communicating with the port 60. The spacing tube is biased against a seal wedge 90 by a disc spring 98 which also biases the seal wedge 96 against the seal wedge 100. The bias on the seal wedge 100 clamps the flange 103 of the sliding seal 102 against portions of the end block 54, thus holding the sliding seal 102 in place. The bias on the seal wedge 90 is applied against the seal 74 to urge it into engagement with the plug 64 and the body 52.

At the exterior of the insertion lock 12, a handle 104 is connected to the shaft 66 for rotating the plug 64. The plug 64 is shown in an open position in FIG. 1 for admitting the insertion probe 12. The handle 104 may be locked in this open position by a locking bar 108 which is rotatably mounted on the end block 54. A collar 110 surrounds and is secured to an end of the locking bar 108 which passes through the end block 54 and a pin 113 is connected to the collar 110. The pin 113 engages a ring 116 mounted on the handle 104. A spring 112 biases the pin 114 against the ring 116 in the position shown. By rotating the locking bar 108, the pin 113 will be moved clear of the ring 116 and the handle 104 may be rotated to close the plug 64.

Referring to FIGS. 2 and 3, the sample mounting arrangement and control mechanism of the insertion probe 18 is shown in greater detail. The insertion probe 18 includes a housing tube 114 ground on its outer surface to very fine cylindrical finish and has a through bore 115 along its length. A plate 118 includes a portion disposed in the bore 115 and connected to the interior of the tube 114 at its end adapted to be inserted within the ionization chamber 16. The plate 118 also has a portion projecting from the bore 115 at the same end of the tube 114, and the plate 118 is preferably aligned along the central axis of the tube 114. Pivot pins 130, 131, arranged in a staggered fashion, project from opposite sides of the exposed portion of the plate 118. A sample holder 133 having a transverse slot 134 for receiving the pin 130 is pivotally mounted on the pin 130 adjacent one side of the plate 118. Similarly, a sample holder 135 (FIG. 3) having a transverse slot 134' is pivotally mounted on the pin 131 adjacent the other side of the plate 118. Before removal, the sample holders 133, 135 are aligned somewhat parallel to the longitudinal axis of the tube 114 and the open ends of the slots 134, 134' face in opposite directions. Samples 136, 137 are respectively mounted in ends of the sample holders 133, 135 and are secured thereto by screws 138, 138'. It is known in the art to use one sample and a counter electrode in a spark source mass spectrometer. While the members 136, 137 are described as samples throughout the specification, it should be recognized that in practice one will use one sample and a paired member. The paired member will be either a second sample or a counter electrode.

A rodlike control member 139 is positioned in the bore 115 of the tube 114 and extends substantially the entire length of the tube 114. A portion of the control member 139 projects from one end of the tube 114 and the plate 118 projects from the opposite end. A pistonlike sealing member 140 is connected to the control member 139 at its inner end adjacent the plate 118. The sealing member 140 slidably engages the inner surface of the tube 114 to provide a fluidtight seal and thereby prevent contaminating molecules from entering the ionization chamber 16 through the tube 114.

With reference to FIG. 1, the tube 114 has a control slot S at its outer end. The control slot has offset portions 142, 143 aligned somewhat parallel with the longitudinal axis of the tube 114 and a transverse connecting portion 114. A key K is connected to the control member 139 and its movement is guided by the slot S.

A pair of sample positioners 145, 146 are connected to the inner side of the sealing member 140 adjacent the plate 118 and are arranged on opposite sides of the plate 118 for engagement with and control of the sample holders 133, 135 respectively. The sample positioners 145, 146 are aligned somewhat parallel to the longitudinal axis of the tube 114 and are located adjacent sides of the sample holders 133, 135 respectively facing away from the open ends of the slots 134, 134', respectively.

The insertion probe 18 has a locating collar 160 around and secured to the base of the tube 114. A pair of locating pins 161 are carried in bores 162 in the collar 160. Springs 163 normally bias the locating pins 161 outwardly against annular retaining caps 164.

The locating pins, when brought into engagement with end surface 170 of the block 54, locate the probe 18 in its analyzing position as shown in FIG. 1.

The procedure for inserting the insertion probe 18 into the insertion lock 12 and ultimately within the ionization chamber 16 will now be described. The locking bar 108 is rotated to release the handle 104 so that the plug 64 may be rotated and closed. With the plug 64 in closed position, a vacuum is established within the ionization chamber 16. The sample holders and samples are mounted on the plate 118 axially in line with the tube 114, and the insertion probe 18 is partially inserted into the passage 58 of the insertion lock 12 until a seal is established with the sliding seal 102. Next, the plug 64 is rotated to an open position and the pin 113 is engaged with the ring 116 to hold the plug in its open position. With the plug 64 in open position, the insertion probe 18 is advanced to the cleaning position adjacent the electrode 50. In this position the samples are in the ionization chamber 16 and surrounded by the cleaning electrode 50 shown in phantom in FIG. 1.

A purge flow of argon is then caused to flow through tube 175 and space 17 into the source region giving a pressure of about 0.02 torr. A high positive voltage is applied to the electrode 50 to produce a high-voltage discharge. Ions produced in the discharge bombard the surface of the samples 136, 137, thus etching or eroding the surface of the samples by a process referred to as sputtering. This erosion occurs equally over the surface of the samples 136, 137 to clear off foreign matter and any oxidized surface which may be present.

The purge flow of argon is then stopped allowing the pressure in the ionization chamber 16 to fall as the vacuum is reestablished. The insertion probe 18 is then advanced to the analyzing position, which is the position of the probe shown in FIG. 1, so that the sample holders are adjacent the electrode mounts 30, 32. At this time the samples are in the position shown in FIGS. 2 and 3. The key K is at the upper end of the slot portion 142 so that the positioners 145, 146 maintain the samples in that position.

The samples are then positioned in the electrode mounts 30, 32. To accomplish this, the control member 139 is withdrawn axially until the key K is at the juncture of slot portions 142, 144. At this time the sample holders 133, 135 are free to rotate approximately 90.degree. about the pins 130, 131 since the sample positioners 145, 146 and the sealing member 140 are retracted to a position indicated in the dotted lines in FIG. 2.

The control member 139 is then rotated to a position in which the key K is at the juncture of the slot portions 143, 144. This rotation causes the positioners 145, 146 to engage and rotate the sample holders 133, 135 approximately 90.degree. from their initial axially aligned position. The sample positioners 145, 146, the sample holders 133, 135 and the samples 136, 137 are then in the positions of FIGS. 1 and 4 with the samples 136, 137 aligned parallel and projecting in opposite directions. At this time, the sample holders 133, 135 are supported by the sample positioners 145, 146 respectively, as indicated in FIG. 1 and by the solid line in FIG. 4. The manipulators 22, 24 are then moved toward the sample holders 133, 135 to a position at which the slots in the electrode mounts 30, 32 may receive the sample holders 133, 135 respectively and secure them by friction, or other means. The control member 139 is then retracted to a position in which the key is at the lower end of the slot portion 143 and the sample positioner 145 is at the position shown in phantom in FIG. 4.

The probe is next shifted axially inwardly depressing the plungers 161 in the bores 162 against the action of the springs 163 until the collar abuts the end surface 170. This axial shifting of the probe removes the pins 130, 131 from the slots 134, 134'. The sample holders 133, 135 are then moved by operating the manipulators 22, 24 a sufficient amount to allow the insertion probe 18 to be withdrawn. The probe is partially withdrawn to allow closing of the plug 64 while the probe still seals the passage 17. The plug 64 is then closed, and the insertion probe 18 is removed from the insertion lock 12.

The ionization chamber 16 is continuously vacuum pumped while the samples are in the analyzing position. With the samples 136, 137 held in the electrode mounts 30, 32, an arc is produced between the samples 136, 137. The arc may be produced by any one of the three following method:

1. A high-radio frequency voltage;

2. A high-voltage pulse followed by a low-voltage DC arc; or,

3. A mechanical vibration arranged to cause intermittent contact between the electrodes supplied from an inductive low-voltage power supply. The electrodes are maintained at a DC voltage such as 20 kilovolts positive with respect to ground and the ions formed in the arc are accelerated by this voltage to a plate (not shown) maintained at ground potential. Ions pass through a hole in this plate for analysis by the mass spectrometer.

An alternative ion source arrangement is shown in FIG. 5. In this arrangement, the tube 114' holds an insulator support 150. A single sample 152 is mounted on the insulator support 150. An inset structure 154 is connected to the enclosure wall 14' and includes a window 156 at one end. A laser beam 157 is projected from an externally positioned laser generator 158 through a lens 159 and through the window 156 upon the sample 152. Procedure for using this arrangement differs from the above-described procedure in that the tube 114' remains within the ionization chamber 16' during ionization of a single sample 152 by the laser beam 157.

Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

Claims

I claim:

1. In an ion source for a mass spectrometer the improved combination comprising:

a. structure defining an evacuable ionization chamber and a cleaning station in the chamber,

b. an insertion probe for introducing at least one sample to be analyzed into the ionization chamber while it is in an evacuated state;

c. a valve connected to the structure and having a closed position for maintaining a vacuum in the evacuable chamber; though also having an open position for admitting the insertion probe;

d. cleaning means connected to the structure and adapted to clean a sample when in the sample cleaning station;

e. ionization means carried in the chamber and defining an ionization station; and,

f. said probe being insertable through the valve to position a sample carried by it selectively and one at a time in the cleaning and ionization stations.

2. The device of claim 1 wherein the cleaning means is within the chamber.

3. The device of claim 2 wherein the cleaning means is a first electrode means which cleans the sample by etching through ion bombardment.

4. The apparatus of claim 3 wherein the first electrode means comprises an annular electrode adapted to partially surround the sample and clean the sample by ion bombardment.

5. The apparatus of claim 1 wherein the ionization means is a laser generator positioned to direct a laser beam at the sample.

6. The apparatus of claim 1 wherein the insertion probe comprises:

i. a tube;

ii. a rod axially movable within the tube; and,

iii. at least one demountable sample holder connected at one end of the insertion probe.

7. The apparatus of claim 1 wherein the ionization means includes at least one electrode assembly including movable sample mounting means for holding the sample.

8. In a mass spectrometer of the spark source type, the combination of:

a. structure defining an evacuable ionization chamber;

b. an insertion probe for introducing at least one sample of material to be analyzed and a paired member into the chamber, the insertion probe including means for demountably securing such sample and paired member thereto;

c. valve means connected to the structure and having a closed position for maintaining a vacuum in the evacuable chamber and an open position for admitting the insertion probe;

d. electrode structure within the chamber for receiving the sample and the paired member in an analyzing position; and,

e. said combination including a sample positioning means actuatable from outside of the ionization chamber for transferring the sample and the paired member from the probe to the electrode structure.

9. The apparatus of claim 8 wherein the sample positioning means is part of the insertion probe and wherein the probe comprises:

i. a tube;

ii. a control rod movable within the tube;

iii. a sealing member disposed in the tube and connected to the control rod;

iv. a plate connected to the end of the tube;

v. a pair of sample holders pivotally mounted on opposite sides of the plate;

vi. the sealing member including projecting elements each overlying a side of the plate for rotating the sample holders; and,

vii. the rod being retractable relative to the tube to retract the projecting elements so that the sample may be removed.

10. In a mass spectrometer of the spark source type including source structure defining an evacuable ionization chamber, the improvement which comprises:

a. an insertion lock connected to the source structure;

b. said lock having internal surfaces defining a passageway communicating with the chamber and a valve for selectively opening and closing the passageway;

c. the internal surfaces including a sealing portion, the valve being positioned between the sealing portion and the chamber;

d. an insertion probe including an external sealing surface of the contour of the sealing portion and adapted for sliding movement through said sealing portion while maintaining vacuum sealing engagement therewith;

e. said probe including means for carrying a sample and a paired member near one end thereof whereby to position the sample and paired member in the chamber when the probe projects through the passage;

f. said valve including an opening sized to receive the probe when the probe positions the sample and paired member in the chamber;

g. said probe including structure effecting a seal within the contour generated by said sealing surface whereby to prevent the admission of gases through said probe into said chamber when the probe is in the passageway; and,

h. spark means associated with said chamber for establishing a spark between the sample and the paired member when the two are in the ionization chamber.

11. The spectrometer of claim 10 wherein the paired member is a second sample.

12. The spectrometer of claim 10 wherein the paired member is a counter electrode.

13. The mass spectrometer of claim 10 wherein the spark means includes a pair of electrode members in the chamber and wherein said probe includes manipulating means for positioning each of the samples and the paired member in a different one of the electrode members.

14. The method of operating a spark source mass spectrometer comprising the steps of:

a. positioning a sample on an insertion probe;

b. passing the probe through an insertion lock to position the sample in an evacuated vacuum chamber while the vacuum is maintained in the chamber;

c. cleaning the sample while in the chamber;

d. bringing the sample into contact with an electrode structure and into an analyzing position in the chamber while still maintaining the vacuum; and,

e. establishing a spark between the sample and a paired member in the chamber.

15. The method of claim 14 wherein the step of bringing the sample into contact with an electrode and into an analyzing position includes the step of transferring the sample from the probe to the electrode structure.

16. The method of claim 15 wherein the step of transferring the sample to the electrode structure includes the step of rotating a sample holder from a position longitudinal of the insertion probe to a position transverse with respect to the axis of the insertion probe.

17. The method of claim 15 wherein the probe is partially withdrawn before a spark is established between the sample and a paired member.

18. The method of claim 14 wherein the step of cleaning the sample includes admitting a purging flow of inert gas into the chamber and thereafter reestablishing the vacuum.

19. The method of claim 18 wherein the inert gas is argon.

20. The apparatus of claim 19 wherein the sample positioning means is part of the insertion probe and wherein the probe comprises:

i. a tubular body;

ii. a control element disposed within the body and movable longitudinally and rotatably relative to the body while in sealing relationship therewith;

iii. said body having a central longitudinally extending member at one end thereof;

iv. a sample holder mounted on said member; and,

v. means on an end of the control element adapted to contact and manipulate the sample holder on movement of said control element to shift the sample holder from a position longitudinal of the probe to a position transverse

of the probe. 20. The method of claim 14 wherein the sample is cleaned with an electrode and the cleaning is accomplished by etching through ion

bombardment. 22. The method of claim 21 wherein the electrode is an annular electrode and the sample is positioned at least partially within

the annular electrode when it is cleaned. 23. In a mass spectrometers of the spark source type, the combination of:

a. structure defining an evacuable ionization chamber;

b. an insertion probe for introducing at least one sample of material to be analyzed into the evacuated chamber, the insertion probe including means for demountably securing such sample thereto;

c. valve means connected to the structure and having a closed position for maintaining a vacuum in the evacuable chamber and an open position for admitting the insertion prove;

d. electrode structure within the chamber for receiving the sample in an analyzing position;

e. said combination including a sample positioning means actuable from outside of the ionization chamber for transferring the sample from the probe to the electrode structure;

f. said sample positioning means including structure in the probe for maintaining a sample carried by the probe disposed substantially longitudinally of the probe during insertion and for moving the sample support to a position transverse of the probe after insertion; and,

g. said sample positioning means also includes movable portions of said

electrode structure adapted to transfer a sample from the probe. 24. The combination of claim 23 wherein the sample support is moved from its longitudinal to its transverse position by rotation of the sample support

member. 25. The method of operating a spark source mass spectrometer comprising the steps of:

a. positioning a sample on an insertion probe;

b. passing the probe through an lock to position the sample in an evacuated vacuum chamber while the vacuum is maintained in the chamber;

c. rotating a sample holder from a position longitudinal of the insertion probe to position transverse with respect to the as of the insertion probe and bringing the sample into contact with an electrode structure and into an analyzing position in the chamber while still maintaining the vacuum; and,

d. establishing a spark between the sample and a paired member in the

chamber. 26. In a mass spectrometer, the improved combination comprising:

a. structure establishing an evacuable chamber and a sample insertion passage communicating with the chamber;

b. ionization means establishing a sample ionization stain within the chamber and including means to ionize a sample positioned at the ionization station;

c. valve means connected to the structure for selectively closing said passage to maintain a vacuum within the space;

d. said structure establishing a path of sample travel from external of said structure through said valve means to said ionization station;

e. an insertion probe adapted to transport a sample from a position external of said structure along said path to said ionization station; and,

f. cleaning means along said path and within said chamber for cleaning a sample within said chamber after it has been moved along said path past

said valve means by the insertion probe. 27. The mass spectrometer of claim 26 wherein said cleaning means establishes a cleaning station

between the valve means and the ionization station. 28. The combination of claim 26 wherein said cleaning means includes means to admit a purging

flow of gas after a sample has been cleaned. 29. The combination of claim 26 wherein the cleaning means includes an electrode adapted to clean a

sample by ion bombardment. 30. The device of claim 29 wherein the electrode is an annular electrode adapted to partially surround the sample

and clean the sample by ion bombardment. 31. The method of positioning a sample in a spark source mass spectrometer comprising the steps of:

a. mounting a sample and a paired member on a single insertion probe;

b. inserting a probe into an insertion lock to establish a vacuum seal therebetween;

c. opening a valve in the insertion lock and thereafter inserting the sample and paired member into an evacuated ionization chamber by passing the insertion probe through the valve, and,

d. thereafter establishing a spark between the sample and the paired member

to ionize portions of the sample. 32. The method of claim 31 including the step of transferring the sample and paired member from the probe to electrode structures within the evacuated chamber prior to establishing a

spark. 33. The method of claim 31 wherein the paired member is a second

sample. 34. An insertion probe comprising:

a. a tube;

b. a control rod movable within the tube;

c. a sealing member disposed in the tube and connected to the control rod;

d. a plate connected to the end of the tube;

e. a pair of sample holders pivotally mounted on opposite sides of the plate;

f. the sealing member including projecting elements each overlaying a side of the plate for rotating the sample holders; and

g. the rod being retractable relative to the tube to retract the projecting

elements so that the sample may be removed. 35. An insertion probe comprising:

a. a tubular body;

b. a control element disposed within the body and movable longitudinally and rotatably relative to the body while in sealing relationship therewith;

c. said body having a central longitudinally extending member at one end thereof;

d. a sample holder mounted on said member; and,

e. means on an end of the control element adapted to contact and manipulate the sample holder on movement of said control element to shift the sample holder from a position longitudinal of the probe to a position transverse of the probe.