A Gallium-Glass Heated Inlet Valve for Mass Spectrometry Carl P. Lewis and Herman D. Hoberecht, Olin Research Center, Olin Mathieson Chemical Corp., New Haven, Conn.
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use of mass bpectrometry to examine materials of low volatilit,y, a variety of methods to introduce samples have appeared in the literature. Cine of the most succes.sfu1 of these is the heated, glass inlet of Lumpkin and Taylor (1). -1s el ed by the sbuthors, this inlet offer3 many advantages, but certain practical difficultiei have been encountered in its use. Saniely, a relamass of molten gallium d into place and held there x i t h a magnet; and, it is difficult to adequately control the temperature of the sample. The heavy mass could be supported by a sufficiently strong magnet, but the moT ing gallium pool remains somewhat awkward. Inadequat,e control over the temperature i.: a more difficult problem to overcome, and, during t'he initial pump-down period, it is possible to lose a reasonable volatile compound (such a3 an iiidole or a urethane) or fractionally distill away the more volatile componmts of a mixture. Hon-ever, these proble ns may be readily conquered n-ith a h q i l e modification in t,he original de-ign. I f one inverts the ga,lliuni valve arrangement and alters the glawxire a? shown in Figure 1, the I I H THE IKCREAS:?;G
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Figure 1 . Diagram of g a Ilium-g la ss heated inlet valve for mass spectrometry
difficulties described aboi e are elinlinated. The gallium pool is stationary; the magnet does not ha7-e t o lift and support the gallium; and the -ample may be cooled during evacuation of the system and introduced into the instrument ab desired. The dimensions of the inlet valve shown in Figure 1 are slightly different than those given by Lumpkin and
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Taylor. In particular, the distance between the rough pump, vent line, and the site now utilized for the gallium reservoir has been lengthened. This permits the heating tape to be 11-ound n ell ab01 e the valve cap so as to ensure heating of the cap and prevent sample condensation. Operation and operating conditions of this unit are essentially the same as described by the original author>, and points of departure may readily he iiwalized from a study of Figure 1. .1 variety of sample containers may be introduced and easily retriel ed with the aid of a small piece of appropriately fashioned rubber tubs ing on the end of a g l a ~ rod. The gallium-g1a.q heated inlet valve deqcribed in this communication has been in uqe in our laboratories for over a year. It has proven to be a convenient, inexpensive. and trouble-free device. In no case have we detected thermal decompo&ion due t o the presence of the g a11'ium. LITERATURE CITED
(1) Lumpkin, H. E., Taylor, G . R., AYAL. CHM. 33, 476 (1961).
Glass Filter Paper Suspension of Precipitates for liquid Scintillation Counting Donald R. Johnson aiid John W a r d Smith, Laramie Petroleum Research Center, Bureau of Mines, U. Interior, Laramie, Wyo.
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suspension of radioactive precipitabes provides a simple! direct preparation method for scintillation counting,. The tecliniquc minimizes problmis deniming from tedious precipitate handling and promotes high counting efficiencies. It ~-ic~lds stisfactory : t s m p on samples of low specific activit) d i e r e liyamine disorption fails because of the quenching produced by the rl3quired absorption of large amounts of SOt and COS (3). Suqiensions of 13aS:I5O4and 13aC1403 have been successfully prepared and counted bj- the follov~ingmethod. LASS FILTER PSI'ER
T'wi)are :iqucou,- soliitions of 1:iI)eled or C 0 3 - ?by ab iorption of gaseous combustion prodiicts in aqiieoua alkali o r other appropriai e mcdium. I'reciliitate 13aS04 o r 13aC03 by adding I~:LCI?.Transfer t,lie precipitate quantit,atively to a glass filter paper (Whatman Glass Paper S o GF, C, 11.0 cni.).
\Tad1 the precipitate and paper tlioroughly n-ith water, then n-ith dioxane or another solvent compatible with the ,scintillator medium (for esamplr, ethylene glycol monomethyl ether). Place the glass filter paper with the precipitate in a 20-ml. counting vial containing nhout 17 ml. of dioxane xintillator wlution { 5yL naphthalene, 0.7% 2,5diI)lienyloxazole, 0.0570 1,+his [2-(5~dienylosazoyl)]benzene in 1 liter of diox?ne ] ( 1 ) . Sliake vigorously until the glass paper is finely divided and uniformly suapendcd. Count the SIHpeii4on in the usual mxiner.
To evaluate the effect of g1aa.j filter paper on the absolute counting efficiency, six samples containing >pecific amounts of labeled sulfuric acid (0.0075 pc. to 0.225 pc.) in dioxane scintillator solution mere counted iyith efficiencies After glass filter averaging 37.37,. paper n-astdispersed in each of the six
S. Department
of the
wiiples, the counting efficiencies averaged 37.07,. BaS04 precipitates prepared from the same six amounts of labeled sulfuric acid counted in glass filter ruspension gave efficiencies averaging 35.07,. Change in amount' of activity and in acid concentration produced no corresponding change in efficiency, and blie difference in counting efficiency for the three conditions was not significant. Consequently, glass filter paper does not quench the sciiitillation, and the method provides efficiencie-, satisfactory for radioactive assay. Background counts on 10 glass filter paper suspensions in dioxane scintillator solution averaged 49.6 =t1.4 c.p.m. (~i-ith95% confidence limits). The glass filter materia! accounted for about 5.5 c.1i.m. of this-total background. Present methods for assaying precipitates require time consuming steps of precipitation, filtering. firing or drying, VOL 35, NO. 12, NOVEMBER 1963
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