Mass Specirometer All-Glass Heated Inlet Lowell Peterson, General Mills Central Research Laboratories, Minneapolis, Minn.
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s MASS spectrometry has gained popularity in the study of high molecular weight compounds, innova tions have appeared in inlet systems which reflect the specialized needs of individnal laboratories. A gallium frit inlet was one of the early designs (6). Advantages were claimed later for a gallium ori6ce (8). One worker employed a Teflon cup for sample introdnctiou ( 1 ) . Another laboratory (S) seals samples in low melting indium capillary tubes and drops them through a glass ball valve into the heated inlet chamber. Glass ball valves were also emoloved in an inlet designed to accept small ;ample tubes (8). Still another design (4) uses a sample cup and gallium valve in a different arrangement. Recently, a versatile system ww described (6) which employs a number of sampling accessories for different types of samples. The wide variety of samples en countered in this laboratory intrc duced problems not solved by previousl, disclosed designs. Metal parts had been reported to cause decomposition of steroids in gas chromatographs, so metal valves and gallium and indium inlets were not considered. Although samples of 1 mg. would be used most freauentlv. some samnles-e.e.. eas ch&nato"graphic fractions-wozd -be smaller than 0.1 mg., and would suffer by dilution to a conventional 3-liter volume. These problems and other smaller ones led to the design of an all-glass inlet system which has been in satisfactory o p e ration for more than a year. Temperatures to 350" C. have been used. Samples are prepared in sealed or unsealed glass capillaries. The inlet system is not intended to replace the metal block inlet often supplied with the Consolidated 21-103C mass spectrometer, but operates in parallel with it through a separate gold leak. DESCRIPTION AND OPERATION
The inlet system is mounted in an oven between the magnet and control cabinet of a m o d ~ e dConsolidated 21103 mass spectrometer. Samples of approximately 1 mg. are weighed into capillary tubes and placed in the sample cartridge (center section, Figure 1) which holds up to 18 samples. The cartridge is then lowered with a hook into the cartridge chamber, A (Figure 2). The chamber is closed and evacuated with a roughing pump. Sample capillaries are released, one a t a time, with knob B. They fall through the Teflon stopcock, C, and unlubri-
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ANALYTICAL CHEMISTRY
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PREPARATION OF SAMPLES
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Figure 1. Cartridge assembly showing cartridge chamber (bottom), somple cartridge (center), and cap (top)
Figure 2. Scale drawii'g of heated inlet
cated glass valve, D, into breaking position L. Valve D is closed by lowering magnet M , and the capillary is broken with a magnetically operated, glass-encased steel breaker E. Plunger F operates the hinge-mounted magnet, G, which operates the breaker. Normally valve H is left open and the sample expands into the 3-liter flask, I . With samples smaller than 0.1 mg., however, this valve is left closed reducing the expansion volume tenfold. Valve J admits the sample to the gold leak and could be eliminated for most purposes. After completion of the scan the sample is pumped out through valve D. Pumpout time depends, of course, on temperature and volatility, but rarely exceeds 5 minutes when steroids containing several polar groups and having molecular weights near 400 are run a t 225" C. (7). Broken capillaries slide down the inclined glass tubing into flask K. A year's accumulntion of broken capillaries did not contribute noticeable background or lengthen pnmpout time by sample absorption.
E m a x 34505 melting point capillaries are broken to 3 em. and then etched near the middle to ensure easy breaking in the inlet system. Many tubes can be broken simultaneously by lining them up on a flat surface and scratching them with a piece of glass cutting wheel. The canillarv tubes are chareed bv different tech&nes depending %n thk state of the sample. Powders, of
course, are easv to insert. Liquids are inserted with a microsyringe or a drawn out glass capillary. Very small liquid samples are sometimes taken up in a short, fine capillary which is then thrust into a regular sample capillary tube. Waxes known t o be homogeneous sometimes are taken from a bottle with a hypodermic needle and ejected into the sample capillary with a wire plunger. The capillaries need not be sealed if the sample is not volatile at room temperature. Volatile samples, however. would be lost during evacuation of the c-artridge chamber and must be sealed into their capillary tubes. This is easily accomplished by first melting the tip of a glass rod in a small flame and quickly touching the melted tip t o the open end of the capillary and removing it. The sample in the bottom of the capillary is thu- qxired exposure t o high temperature. DETAILS OF CONSTRUCTION
The sample cartridge (center section, Figure 1) ivas made of glass for clear visibility: otherwise, brass could be used in the same basic design. The cartridge consists of two basic parts. The first is a stationary outer cylinder. which contains capillary compartments, and rests by its outer rim, A , on a ring inside the cartridge chamber below.
The second part is a slotted disk, B, attached to the cylindrical core, C, and can be rotated with the knob, D, after fork E engages the crossbar on assembly. When the slot in disk B is rotated under one of the compartments, the capillary in that compartment drops. Because some difficulty was experienced in removing the joint, G, to open the cartridge chamber, the brass assembly, H , wa5 cemented on to this section. The seal can now be broken easily by turning the knurled screw down onto brass ring I . Experience has shown that tn-o knurled screm would have been enough. Most construction details for the glass parts are apparent from Figure 1 or Figure 2. Valves were fashioned from hand-lapped lSi9 ball and socket joints and tested for leakage before installation. The funnel which supports the capillaries erect for breaking in position L IT-as supported by studs so that sample evacuation would not take place through a narrow constriction. The gold leak was placed inside the oven rather than in the heated line to the ion source since uniform temperature is more difficult to achieve in the heated line. -4cool spot is less serious on the low pressure side of the gold leak than on the high pressure side, because it is less likely to condense the sample. The magnets chosen as valve lifters
for this high temperature operation were F-1404 Indox ring magnets. Three magnets, encased in a brass sheath, were used for each valve. Four F-1404 Indox ring magnets were used for the sample breaker. The latter were cut to resemble a doughnut with one bite removed. The magnets were obtained from Indiana Steel Products Co., Valparaiso, Ind. ACKNOWLEDGMENT
The author gratefully acknowledges the help of Emil Benz and Arthur Haut in constructing the glass parts for this inlet system and providing suggestions which were accepted in its design. LITERATURE CITED
(1) Caldecourt, T'. J., ANAL. CHEM. 27, 1670 (19551. (2) Genge, C: A., Zbid.,31, 1747 (1959). (3) Grubb, H. M., Ehrhardt, C. H.,
Vander Haar, R. W.,Moeller, IT. H., ASTM Committee E-14 Meeting, Los Anrreles. 1954. (4) Limpkin, H. E., Taylor, G. R., ANAL.CHEX 33,476 (1961). (5) McAdams, D. R., Harris, R. J., ASTM Committee E-14 Meetinn, Chicago, 1961. 16) O'Neal. RI. J.. Wier. T. P.. Jr.. ANAL. CHEU.23,830 (1951). (7) Peterson, L. E., Chem. Znd. (London) 1962, 264.
(8) Ryhage, R., d r k i c Kema, 16, 19 (1960).
VOL 34, NO. 13, DECEMBER 1962
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