to a beaker with water, and a final rinse with hydrochloric acid completed the transfer. The sample was evaporated to remove water. The residue \\-as dissolved in hydrochloric acid and filtered through glass no01 into a separatory funnel. The volume of solution was made up to 27 ml. with hydrochloric acid, and 5 ml. of water were added. Dithiocarbamate Extraction. Extractions were carried out with at least three portions of dithiocarbamate solution, first from t h e approxiniately 3 . 3 5 hydrochloric acid solution of t h e mineral piepared as described above, and again after dilution n i t h 11-ater t o 1 . 5 s . I n the case of sphene, a 1 to 9 dithiocarbamate solution was used. The organic matter in extract ii was destroyed with hot nitric-perchloric acid; the acid solution was diluted with water and filtered into a separatory funnel as in the dithiocarbamate procedure. Dithizone Extraction. Lead in ex-
tract ii\f-as determined bythe dithizone procedure, except t h a t 2 ml. of a saturated solution of ammonium tartrate 51 ere added to keep in solution traces of salts sometimes carried over with the dithiocarbamate extract, and to prevent extraction of indium. The results are recorded in Table IV. ACKNOWLEDGMENT
This investigation was assisted by a grant from the university’s Advisory Committee on Scientific Research, for which grateful acknowledgment is made. One author (A. D. 11.) was holder in turn of fellon-ships given to the university by Canadian Industries. Ltd., and by Union Carbide Corp. of Canada, for n-hich thanks are here recorded. The authors are also grateful to J. T. Kilson (Geophysics) and his associates at the University of Toronto for friendly interest and helpful discussions relating to this ivork.
LITERATURE CITED
(1) Biddle, D. -A,, IND.ESG. CHEM., ANAL.ED.8, 99 (1936). ( 2 ) Cooper, S,S.,Sullivan, 11.L., .ASAL. CHEX. 23, 613 (1051) 1 3 ) Gane. J. C.. dnalvst 80. 789 11955). )(: 4 ) Hayt,’ Ha& H. I-.’, I-.,Ibid.; I b z d ; 76, 602 (1951). ’ H , Risdon, E. J Andrea, ( 5a ) Irving, H., C, S o c 1949,’537. 1940.’15.37. G.,. .TJ. Chmn Chem. SOC. ((6) 6 ) Lockwood, H. G., dna21yst 79, 143
(1954). 171 Rosenavist. I. T.. A m . J. Sci. 240, 356 11942). (8) Sandell, E. B., “Colorimetric Determination of Traces of Metals,” 2nd ed., Interscience, Sew York, 1950. (9) Ibid., pp. 307-8. (10) Strafford, T.,T \ - \ : i t t , P. F., Kershan-. F. G.. zlrzniiist 70. 232 (1945). (11) I b i d . , 78,624 (1953). (12) Tomp-sett, S. I,., Ibid., 81, 330 (1936).
RECEIVEDfor review March 12, 1057. Arcepted June 3, l 9 5 i .
Thermal Conductivity Behavior Importance in Quantitative Gas Chromatography DOUGLAS
M. ROSE
and ROBERT L. GROB’
Products Research Division, Esso Research and Engineering Co., linden, N. J.
b The thermal conductivity behavior of a variety o f hydrocarbons was investigated as a preliminary step toward better quantitative interpretation o f gas-liquid chromatographic data. Differences in response output of a thermal conductivity cell for sirnilar hydrocarbons may b e significantly large. By making corrections for each compound, precise qucntitative results are obtained.
A
S U h l B E R of
papers dealing with gasliquid chromatography (1-4, 6) have directed attention to quantitative interpretation of the data available from chromatograms. The main effort had been concerned with the choice of substrates, apparatus, and, in general, operating conditions for the resolution of various systems. This paper deals with the quantitative aspect of the technique. T h e n a thermal conductivity cell is used as the detector, it is advantageous t o use a carrier gas t h a t has a thermal conductivity vastly different from any compounds to be determined. Because Present address, Department of Chemistrv, Wheeling College, IYheeling, IT-.Va.
thermal conductivity is inversely related to the square root of the molecular weight, the molecular n-eight of the carrier gas should be extremely small or extremely large, in order to obtain as large a response as possible from the detector. The fact that helium has a lorn- molecular weight and is safe to handle makes it a suitable choice. The chromatogram is usually a plot of the response-output of the thermal conductivity cell against time (or volume of carrier gas). The area under a peak due to a single component, divided b y the total area under all the peaks, is sometimes related directly to the mole or weight per cent of that compound. The area associated with any given conipound is referred to as per cent area. Hausdorf ( 6 ) states that when helium is used as the carrier gas, the difference in its thermal conductivity and t h a t of the compounds most frequently analyzed is large, and all molecules may be assumed to have the same thermal conductivity in the first approximation. If it is further assumed t h a t the response of the thermal conductivity cell varies linearly with the concentration, the peak areas would be expected to be a direct measure of molar concentration. This assumption sometimes leads to sizable errors.
Other authors (2-4) have stated that the areas more closely represent the n-eight concentration of a mixture. Clearly this relation could be further improved b y calibration ( 2 , page 296). This paper records a series of such calibration factors, not only for direct use b y other workers in the field, but also as a basis upon which a suitable theory niay be ultimately established. Inability to obtain satisfactory quantitative results b y relating per cent area to mole per cent or weight per cent prompted this investigation of the thermal conductivity behavior of a variety of hydrocarbons. APPARATUS A N D MATERIALS
The hydrocarbons studied were of the highest purity obtainable from the Kational Bureau of Standards, Washington, D. C., or the American Petroleum Institute, Carnegie Institute of Technology, Pittsburgh, Pa. The instrument mas a Model 154 vapor Fractometer manufactured by the Perkin-Elmer Corp., Norwalk, Conn. The recorder was a 10-mv. Leeds &Northrup Speedomax recording potentiometer which had a 2-second fullscale response time. The chart paper used was Leeds 8: Northrup, No. 742. The partition columns were A columns purchased from the PerkinVOL. 29, NO. 9, SEPTEMBER 1957
1263
Table I.
Compound n-Pentane n-Hexane n-Heptane n-Octane n-Nonane n-Decane Benzene Toluene Ethylbenzene o-Xylene nL-Xylene p-Xylene Isopropylhenzene n-Prop>-lhenzene p-Ethyltoluene 1,2,4-Trimethylbenzene 1,3,5-Trimethylbenzene see-Bnty llenzene 2,2-Dimethylbutane 2,3-Diniethylbutane 2-hlethylpentane 3-hlethylpentane 2,ZDimethylpentane 2,4-Dimet hylpentane 2,2,3-Trimethylbutane 2,3-Dinwthj-lpentane 2-Methylhexane 3-lleth>.lliexane
Relative Response per 3Iolea 105 12:3 14:3
3-ethylpent me
2,2,4-Triniethylptntane Cyclopentane 3lethylcJ-clopentane 1,l-Diniethylcyclopentane
I
