5’,2
=
s,2 -
Sk2
The resulting values of S, are: toluene 0.5, benzene 1.45, hexadecane 1.27, and octadecane 2.07. Their weighted average is 1.25y0, n hich estimates the error inherent in the method plus other uncontrolled variables. Hence, the method is as good :is the ability to sample in gas chromatography, and can doubtless be improved by study of technique and further replication of samples. Table IT’ shows the correlation among the four compounds from the scintillation counter c ata, arbitrarily using toluene as the standard. The deviations again show a relative error of around 1%. ACKNOWLEDGMENT
Scintillation counting was performed through the courtesy of J . Meade, Univerhity of CaliforniE a t Los -4ngeles. We are indebted to It. C. Hames, Applied Physics Corp., for suggestions during the rxperiment:il work and for reading the manuscript
Table IV. Correlation among Compounds Compound n1v. mv./pl. mpc./d.4 mpc./@Lb 22.7 74.9 22.7 Toluenec 29‘3.7 74.0 22.4 22.6 Benzene 295.5 29.7 29.6 98.0 Hexadecane 391.8 21.2 21.4 70.1 Octadecane 280.5 Calculated from ion chamber rrsults using toluene as standard. * Measured with scintillation counter. Std. LITERATURE CITED
(1) Caeace, F., IYucZeonics 19, No. 5, 45-50
(1961). (2) Dutton, H. J., Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, March 1961 13) F‘,IBarnes. . J. L.. “Tran~, Gardner. & sients in Linear systems’,” voi. 1, pp. 262-3, Kilev, Kew York, 1961. (4) Gordus, A. A., Saver, ic4. C . , Jr., Willard, J. E., J . Am. Chem. SOC.79, 3254 (1957). (5) Karmen, A., Giuffrida, L., Tritch, H., Nature 186, 150 (1960). (6) Selson, D. C., Ressler, P. C., Jr., Hawes, R. C., ANAL. CHEM.35, 1575 (1963). (7) Popjack, G., Lowc, A. E., Moore,
l>1:v. ... 0.2 0.I
0.2
D., Brown, L., Smith, F. A,, J. L i p i d Res. 1, 29-40 (1959). (8) Whittemore, I. M., Rio-Organic Chem. Quari. Rept., Univ. of Calif. Radiation
Laboratories, UCRL-9408, 49-50 (September 1960). (9) Winkelman, James, Karmen, Arthur, ASAL. CHEM.34, 1067-71 (1962). (10) Wolf, A. P., Radioisotopes in Scientific Research, 1’01. 2, p. 123, Pergamon Press, London, 1957. (11) Wolfgang, R., Mackay, C. F., A‘ucleonics 16, No. 10, 69-73 (1958). (12) Wolfgang, R., Rowland, F. S., ANAL.CHEM.30, 903-6 (1958). RECEIVEDfor review April 25, 1963. Accepted July 23, 1963. Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, March 1963.
Performance of an Instrument for Simultaneous Gas Chroma t o!gra phic a nd Radioactivity A n a lysis D. C. NELSON, P. C. RESSLER, Jr., and R. C. HAWES Applied Physics Corp., Monrovia, Calif.
b An instrument for simultaneous gas chromatography ancl radioactivity analysis i s described. The ion chamber used for the radioactivity measurement i s contained in the same temperature-controlled oven as the normal chromatography detector, and can be heated io over 300‘ C. Data are given for both programmed and isothermal column opzration at high and low temperatures. Specific applications are described. Sensitivity, linearity of response, response times, and resolution are discussed for the entire system. too long aftel, gas chromatography in thc conventional sense nxs well under way in the Gnited States, articles bcgan i o appear on the tirtection of the radioa,:tivity of labcled fr:ictions in addition tcb the mass detection of the) scparatcd cornponents. ‘L’wgvnrral methods nieasuring the :rc%ivity of :t scpar:itctl i~ornponr~nt 11:ivc I ) w i i uhed. One is t o collect thc saniplc on a coated solid scintLlator or in solution, or as the pure mitterial, and then OT
l>f
mw.ure the radioactivity with a counter (3, 6, 7 , I O ) . The second technique, used more often recently. is to measure the activity of the fraction in the flowing gas phase as it leaves the mass detector. As early as 1953, Kokes, Tobin, and Emmett (8) passed actire fractions containing soft beta emitters by a Geiger counter with a thin window. I n 1956 Evans and Killard ( 4 ) measured hard p and y particles in a similar manner. However, it waz soon realized that the window materials of the detectors make for poor efficiency of measurement for soft beta emitters such as C14 and H3, the most active isotopes. M701fgangand Rowland ( I d ) , Kolfgang and Mackay ( I 3 ) , and James and Piper (5) have investigated proportional counters, with and without windows. Dobbs (a),Cacacc ( I ) , and Iinrmcn and Winkelman (7’) have u w d an ion chamber in wries with thc G C drtector. llthough slightly higher sensitivity can lie attained by proportional counting, the ion-cahanibcr techniqur offers t h p advant:tgcs of bring simple, ca
