US3594574A

US3594574A - All-glass heated inlet system for mass spectroscope with sample chamber vacuum seal

Info

Publication number: US3594574A
Application number: US802936*A
Authority: US
Inventors: Thomas D Morgan; Robert J Brunfeldt
Original assignee: Phillips Petroleum Co
Current assignee: Phillips Petroleum Co
Priority date: 1969-02-27
Filing date: 1969-02-27
Publication date: 1971-07-20
Anticipated expiration: 1988-07-20

Abstract

An all glass heated inlet system for a mass spectroscope. The inlet system includes a valved manifold and a vacuum lock for sealingly connecting a sample container to the manifold.

Description

United States Patent 8/1934 Rupp 2,624,008 12/1952 Hickam 250/4 1 .9 2,699,505 1/1955 Usher 250/4l.9 2,767,319 10/1956 Beeton et a1 250/419 FOREIGN PATENTS 161,568 8/1964 U,S.S.R. 250/419 OTHER REFERENCES MASS SPECTROMETRY AND ITS APPLICATIONS TO ORGANIC CHEMISTRY, J. H. Beynon, Elsevier Publishing Company, 1960, pp. 147 168 class 250-419 S Primary Examiner-James W. Lawrence Assistant Examiner-C. E. Church Att0rneyYoung and Quigg ABSTRACT: An all glass heated inlet system for a mass spectroscope. The inlet system includes a valved manifold and a vacuum lock for sealingly connecting a sample container to the manifold.

PATEN TED JUL 20 I97! INVENTORS T. D. MORGAN BY I R. ?RUNFELDT ATTORNEYS ALL-GLASS HEATED INLET SYSTEM FOR MASS SPECTROSCOPE WITH SAMPLE CHAMBER VACUUM SEAL This invention relates to mass spectroscopy. In one aspect it relates to an inlet system for a mass spectroscope.

ln the ideal mass spectroscope, the system is operated at a gas pressure below mm. of Hg. in order to minimize the perturbing effects caused by the collision of ions with gas molecules. in order to introduce the sample into the spectroscope without disturbing the source vacuum, the spectroscope is provided with an inlet system comprising a valved manifold and an expansion vessel. For gases, the introduction of the sample into the system is relatively simple requiring only an inlet connection to the manifold and a glass bulb or reservoir from which the sample is expanded. However, in analyzing high molecular weight compounds which are normally in the liquid or solid-state, a heated inlet system is required to vaporize the sample and thereby obtain sufficient vapor pressure for analysis. Prior to vaporization of the sample, the inlet system must be purged of residual gas and/or air. The conventional purging technique involves evacuation of the system to about l05 mm. of Hg. With the system purged the sample vapors must be introduced therein without loss of vacuum.

The heated inlet system presents serious operational problems. For example, metal valves or joints cannot be used at the elevated temperatures because the metal parts exposed to the system and sample present a source of contamination, particularly at high operating temperatures (in order of 425 C.). Furthermore the sample must be introduced into inlet system without loss of the vacuum lest the system be contaminated. Accordingly an all-glass system was developed which received the sample in a sealed capillary tube. Following evacuation of the system, this tube was broken by the action of a magnet. This approach, however, was tedious and time consuming and therefore was unsatisfactory for laboratory use. Another sample introduction technique involved the use of a gallium covered glass frit inlet or a gallium orifice inlet, but had an upper temperature limit of about 300 C. and retained the property of potential catalytic reaction by contact of the sample with the hot gallium.

The purpose of the present invention is to provide an allglass inlet system fora mass spectroscope which permits rapid introduction of a small liquid or a solid sample without loss of vacuum in the spectroscope source.

A demountable sample container is sealingly held to the inlet manifold by means of a vacuum chamber. The vacuum chamber is fonned of two concentric tubes integrally joined at their upper end and having coplanar flanged portions at their lower ends defining an annular opening. The upper end of the container is flanged presenting an annular flat mating surface for the coplanar flanges of the concentric tubes. Now when the annulus between the chamber tubes is evacuated to a pressure intermediate atmospheric and that of the system, the container flange is forcefully maintained against the mating surface provided by the coplanar flanges of the chamber tubes. The chamber at the intermediate pressure provides a buffer region along the sealing surfaces between atmospheric pressure and system vacuum. With the sample thus sealed, the system is evacuated by manipulation of the manifold valves placing it in a condition for vaporizing the liquid or solid sample. The container and locking chamber are rapidly brought to the vaporizing temperature of the sample whereupon vapors emanate from the vial through the manifold to the inlet system reservoir and thence to the spectroscope.

In summary then, an object of this invention is to provide an all-glass mass spectroscope inlet system with a vacuum lock for rapid introduction of the sample; another object is to provide a mass spectroscope inlet system operable at temperatures up to 560 C.

Other objects and a fuller understanding of this invention may be had by referring to the following description and claims taken in conjunction with the accompanying drawings in which FIG. 1 is a diagrammatic view of the inlet system for a mass spectroscope; and

FIG. 2 is an enlarged sectional view of the sample container and locking chamber shown in FIG. 1.

With reference to FIG. 1, an inlet system 10 for a mass spectroscope shown schematically as 11 is seen to include a valved manifold 12, an expansion vessel 13, and a demountable sample connection assembly 14 incorporating the vacuum-locking apparatus of this invention. A sample container 15 containing the liquid or solid sample is maintained in sealing engagement with the sample connection 14 by means of the vacuum lock, described in detail below.

The manifold system includes permanent magnet control glass ball-

type valves

16, 17, 18 and 19 and manifold piping as follows: line 22 interconnects the vacuum lock apparatus to the upstream side of valve 19; line 23 extends from the downstream side of valve 19 and junctions at the midpoint of another line 24 which leads to the upstream sides of valves 17 and 18; line 25 extends from the downstream side of valve 17 to the expansion vessel 13; line 26 extends from the expansion vessel 13 to the upstream side of valve 16; and line 27 extends from the downstream side of valve 16 to the mass spectrometer 11 and contains a molecular leak 28.

Means for purging the inlet system are provided by a vacuum pump system shown generally as 29 which is connected to the inlet manifold 12 through line 21 and valve 18. The vacuum pump system 29 includes a diffusion pump 31, a rough pump 32, and a source of pressurized gas indicated by arrow 33, and associated

valves

34, 35, 36 and 37 for selectively placing in operation the diffusion pump 31, the rough pump 32, and pressurized gas source 33.

As best seen in FIG. 2, the vacuum lock on the sample container 15 is provided by a pair of

concentric tubes

38 and 39 permanently joined at their upper ends and at the junction with line 22. The lower ends of tubes 38and 39 are flared presenting coplanar flat

annular surfaces

40 and 41, respectively, separated by annular opening 42. The

tubes

38 and 39 define annularly shaped vacuum chamber 38a. The container 15 is in the form of a vial having a flat-faced flange 43 adapted to mate with the

coplanar surfaces

40 and 41 of

tubes

38 and 39. The

mating surfaces

43, 40 and 41 are hand ground to provide a surface flatness within one interference band. The vacuum chamber 38a is connected to a rough pump 44 through line 45 which includes threeway valve 46. Thus when the valve 46 is opened to the rough pump 44, the chamber 38a is evacuated thereby maintaining the flange 43 in sealing engagement on its mating surface provided by

coplanar surfaces

40 and 41. In order to provide sufficient seal, the pressure in the chamber 38a must be in the order of 34Xl0 mm. Hg. Atmospheric line 47 communicates with chamber 38a through valve 46 and line 45 to break the vacuum when changing samples.

ln analyzing the high molecular weight compounds it is necessary to heat the inlet system 10 to vaporize the materials thereby to develop sufficient vapor pressure for the mass spectroscope. Accordingly, a portion of the inlet system 10, as shown in FIG. 1, is mounted in-a constant temperature oven shown generally as 48. in order to provide access to the sample connection 14 a sample heater 49 surrounds the vacuum lock apparatus 14 and the sample container 15. The sample heater 49 is provided with an access door and a 1,000-watt heater so that the temperature of the sample may be raised from room temperature to 425 C. in about 10 minutes.

Thus it is seen that all the parts of the inlet system 10 to which the sample or sample vapors are exposed are constructed of glass. The upper temperature limit at which the system may be operated is dependent upon either sample stability or the annealing point of the glass. (The annealing point of borosilicate glass is 560 C.)

The operating procedure comprises generally the following steps: placing the sample in the container 15; attaching the container 15 to the inlet system purging the inlet system of sample residual or air; and vaporizing the liquid or solid sample. The following discusses each step separately.

Liquid or solid samples may be weighed and placed directly into the container 15, or liquid samples may be measured by liquid volume in precision bore capillary tubing. If the latter procedure is followed, the capillary tubing is sealed at one end and the sample drawn into the capillary by cooling. The tubing then containing the sample is placed in the container 15.

In the standby condition valves l6, l7, l8, 19, 34, and 37 are open evacuating the system 10 of residual sample through diffusion pump 31. Valve 46 is open to the pump 44 vacuum locking the container to the connector 14. Next, valves 16, l7, l9 and 37 are closed and valve 36 opened. Valve 46 is turned to air breaking the vacuum in chamber 38a. The sample container is removed from connector 14 by sliding sideways. After the sample is inserted by one of the above-described techniques the container 15 is reattached and the vacuum again pulled on the chamber 38a by turning valve 46 to the rough pump 44. If necessary, the sample is cooled to prevent premature vaporization. With the container 15 vacuum locked to the manifold 12, valve 35 is opened admitting a dry gas such as nitrogen to the system thereby neutralizing the pressure across valve 19. After valve 19 is opened, valve 35 is closed and valve 34 opened permitting initial evacuation of the system upstream of valve 17 through rough pump 32. Valve 36 is then closed and valve 37 opened and the system evacuated to the operating pressure through the diffusion pump 31. Finally the nitrogen which leaked past valve 17 into the expansion vessel 13 is removed by first opening valve 17 and then valve 16 Valve 18 is then closed placing the inlet system 10 in a condition for receiving the vapors from the sample container 15.

The sample heater 49 is closed around the sample connector l4 and container 15. The heater 49 raises the temperature of the sample to about 425 C. in about l0 minutes. The sample is vaporized, the vapors passing from the container 15 through the manifold 12 to the expansion vessel 13 and thence to the mass spectroscope 11.

The all-glass heated inlet system according to this invention may be used in combination with any spectroscopic device operating at gas pressures below atmospheric. The all-glass heated inlet system is particularly applicable for determining high boiling impurities, for identifying vapors evolved from sulfur-based paint which is applied at elevated temperatures and for analyzing small samples (about 0.l milligrams) separated by gas chromatography, and for analyzing lubricating oils having average molecular weights up to 800. The following examples illustrate some of the applications to which the inlet system according to this invention is particularly applicable.

EXAMPLEI 0.0. of tube 38 O.D.ofthe tube 39 I8 mm. Width of annular opening 42 1 mm. Height of chamber 380 44 mm. thickness of surface 40 8 mm.

thickness of surface 41 8 mm.

OD. of! container l5 18 mm.

Height of container 15 50 mm. Thickness of surface 43 6 mm.

The

pieces

38, 39 and 15 were well annealed for stability during grinding and polishing operation. The mating surfaces 43 and 40-41 were hand ground with successively finer grades of abrasive terminating with 600 mesh silicone carbide. Final grinding was done with a John Crane Lapmaster, using their NO. 1,700 lapping abrasive, providing a surface flatness within one interference band. Before grinding, glass rods slightly smaller than the center tube 38 were cemented into the open end of tube 38 and sample container 15 using optical pitch. The annular opening was also filled with this material. A polisher was made using optical pitch following generally the procedure outlined by Twyman (F. Twyman, Optical Glassworking, Hilger 8!. Watts, London). The polishing was accomplished by hand with ceric oxide. The polished surfaces were finally checked for flatness with a quartz optical flat and monochromatic light.

A 500 mg. sample of the gelatinous hexane extract was deposited in the container 15 and the solvent pumped off at room temperature. The chamber 38a was evacuated to a pressure of about 3X10 mm. Hg. and the inlet system 10 was evacuated to a pressure of about l0"" mm. Hg.

The sample was heated to 200 C. to vaporize the chlorinated components, then to the inlet system 10. Chlorinated compounds were readily identified in the mass spectrometer.

EXAMPLE ll The apparatus described in example I was used to analyze a sample separated by gas chromatography.

A 10 mg. sample of crude oil eluded from a liquid chromatograph was collected in .a small glass trap, refrigerated, and then transferred to the container 15. The container 15 was attached to connector 14 and the vacuums in the order described above pulled on the system. The types of hydrocarbon vapors were readily identified by the mass spectrometer.

EXAMPLE ill The apparatus described in example I was used to analyze a lubricating oil having an average molecular weight of 479. The sample, a 20-stock base oil had been separated into aromatic and saturated portions using a silica gel coated chromographic column. The aromatic portion was placed in sample container 15. The sample container 15 was locked in place by evacuating chamber 38a to about 3X10 mm Hg. After the system was evacuated to about 10 mm. Hg, the temperature of the sample was raised to 425 C. Vapors of monoaromatics and diaromatics were readily identified by the mass spectrometer.

The above examples illustrate the versatility of the inlet system constructed according to the present invention. More specifically it permits the analysis by the mass spectroscopic technique of small samples (in the order of 0.1 mg.) of liquids or solids at relatively high temperatures 560 C.

We claim:

1. An all-glass inlet system for a mass spectroseope comprismg:

an expansion vessel;

a sample inlet line;

a valved manifold interconnecting said sample inlet line,

said expansion vessel, and said spcctroscope;

a sample connector attached to said inlet line with said sample connector having a pair of concentric tubes joined together at their upper ends and open at their lower ends, said lower ends being provided with coplanar flat annular surfaces separated by an annular opening;

A sample container having a flange presenting a flat annular surface particularly sized to mate with said coplanar annular surfaces of said concentric tubes in contacting sealing engagement one with the other, the interior of said sample container being in fluid communication with said inlet line with said container sealed to said connector and said sample container flange contacting the lower ends of the concentric tubes of the sample container sealing the that maintained in said chamber thereby providing a buffer region having a pressure intermediate atmospheric pressure and the evacuated pressure of said container;

an oven for maintaining said expansion vessel and associated manifold at a constant temperature; and

a sample heater disposed around said sample connector, a

portion of said inlet line, and said sample container for increasing the temperature of said sample independent of said oven to a temperature in the range of between the temperature sufficient to vaporize the sample to a temperature of about 560 C. v I 2. An all-glass inlet system for a mass spectroscope, as set forth in claim 1, wherein the pump connected to the vacuum chamber is of a size sufficient to lower the pressure within said vacuum chamber to a pressure lower than about 3Xl'0" mm.

3. An all-glass inlet system for a mass spectroscopic, as set forth in claim I, wherein the evacuating means is of asize sufficient to lower the pressure within the manifold, inlet line, and container to a pressure lower than about 10 mm. Hg. 7

4. An all-glass inlet system for a mass spectroscope, as set forth in claim I, wherein the sample heater is of a size sufficient for raising the temperature of the sample to from about room temperature to about 425 C. in at least about 10 minutes.

UNITED STATES PATmT OFFICE CERTIFICATE OF CORRECTION Patent No, 3,59%571+ Dated= July 20, 1971 Thomas D. Morgan and Robert J. Bruni'eldt It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, line 9 delete "independent and insert than Column 6, line 6 "315L013" should read 3xlO line 11 "10 should read 10" Signed and sealed this 22nd day of February 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Comissioner of Patents

Claims

1. An all-glass inlet system for a mass spectroscope comprising: an expansion vessel; a sample inlet line; a valved manifold interconnecting said sample inlet line, said expansion vessel, and said spectroscope; a sample connector attached to said inlet line with said sample connector having a pair of concentric tubes joined together at their upper ends and open at their lower ends, said lower ends being provided with coplanar flat annular surfaces separated by an annular opening; A sample container having a flange presenting a flat annular surface particularly sized to mate with said coplanar annular surfaces of said concentric tubes in contacting sealing engagement one with the other, the interior of said sample container being in fluid communication with said inlet line with said container sealed to said connector and said sample container flange contacting the lower ends of the concentric tubes of the sample container sealing the annulus between said concentric tubes and forming a vacuum chamber; a pump connected to the vacuum chamber for evacuating said chamber, vacuum locking said sample container to said connector, and maintaining said mating surfaces in sealing relation; means for evacuating said manifold, said inlet line and said container with said container sealably vacuum locked to said connector, and providing a pressure less than that maintained in said chamber thereby providing a buffer region having a pressure intermediate atmospheric pressure and the evacuated pressure of said container; an oven for maintaining said expansion vessel and associated manifold at a constant temperature; and a sample heater disposed around said sample connector, a portion of said inlet line, and said sample container for increasing the temperature of said sample independent of said oven to a temperature in the range of between the temperature sufficient to vaporize the sample to a temperature of about 560* C.

2. An all-glass inlet system for a mass spectroscope, as set forth in claim 1, wherein the pump connected to the vacuum chamber is of a size sufficient to lower the pressure within said vacuum chamber to a pressure lower than about 3 X 10 3 mm. Hg.

3. An all-glass inlet system for a mass spectroscope, as set forth in claim 1, wherein the evacuating means is of a size sufficient to lower the pressure within the manifold, inlet line, and container to a pressure lower than about 10 5 mm. Hg.

4. An all-glass inlet system for a mass spectroscope, as set forth in claim 1, wherein the sample heater is of a size sufficient for raising the temperature of the sample to from about room temperature to about 425* C. in at least about 10 minutes.