Instrument Parameters. Column temperature 160" C., 20 p.s.i., 47 ml. Per minute inlet flow, 2-MIul.sample size, @ to 2-mv- recorder range, across the chart speed of '/2-inch per as the carrier gas* RESULTS AND DISCUSSION
Our inyestigational experiments for the separation of thymol isomers by GLC led to the use of lanolin as a substrate. Such substrates commonly used as rlpiezons L and 11,D.C. silicone 550,
which represent nonpolar types, and Carbowax20MandsucroseoctaacetateJ which represent polar materials, were ineffective in separating the 4- and &isopropyl pair. Lanolin partially separates these two so that suitable quant i t a t h e estimation can be made in mixtures of the four isomers. I n approximately equal mixtures of the four isomers, the separation appears as illustrated in Figure 1. The quantitative results based on geometric a]?prosimation of areas yield sat is factor^ results agreeing to +2?4 from known.
LITERATURE CITED
( 1 ) Carpenter, M. s., Easter, M., erg. chern, 20, 401 (1955). (2) Guenther, E., "The Essential Oils," Vol. 11, pp. 503-5, Van Nostrand, New York, 1952. (3) Porcaro, P. J., Johnston, V. D., ANAL. cHEM, 34, 1071 (1962).
w.
J ,
PETERJ. PORCARO V. DANIEL JOHNSTON Laboratory
The Givaudan Gorp, Delawanna, N. J.
Se p a ration of Menthone-Me ntho1 Stereoiso mers by Gas Liquid Chromatography SIR: K e disclose a gas chromatographic procedure that allows quantitative analysis of a mixture containing the two menthone (I, 11) and four menthol stereoisomers (111 to VI).
hlenthone I
Isomenthone I1
Neoisomenthol Menthol IS' v
CrlQOMOSORB W
Neomenthol I11
Isomenthol VI
The recent procedures developed by Porcaro and Johnston (2) or Moore and Kossoy (1) using Hyprose SP-80, octakis(2-hydroxypropy1)sucrose (The Dow Chemical Co., Midland, Mich.) on 60- t o 80-mesh Chromosorb W allows a clean separation of all four menthol isomers. However, in a mixture that also contains t h e two menthones this procedure gives incomplete separation of isomenthone (11) and neomenthol (111) as illustrated in Figure 1. Replacing Chromosorb W by the recently available Chromosorb W silicon treated (Johns-Manville) allows a separation of the siu isomers a t all concentration levels. Figure 1 (lower part) illustrates the same mixture that failed t o be resolved on nonsilicon treated Chromosorb IT. The packing was 20% by weight and was prepared by evaporative deposition of the Hyprose SP-80 onto silicon treated Chromosorb W. The column mas 0.25-inch 0.d. copper tubing and was conditioned before use. Analyses were conducted at 150' C. column tem1846
I 2 C O L U M N . 150'
ANALYTICAL CHEMISTRY
L v
z a wL a
12 C O L U b l N . I S 0 ' CHROMOSORB W SiLlC3N TREATED
A
R E T E N T I O N TIME, M I N
Figure 1 . Analysis of menthone-menthol mixture on Hyprose SP-80
oerature. 15 D.s.i. helium inlet Dressure, 'and 66 ml. per minute in a Perkjn-Elmer Vapor Fractometer Model 154-D. I
&
ACKNOWLEDGMENT
The author thanks Rudolf Weber and his associates for experimental assistance.
LITERATURE CITED
( 1 ) Moore, D. R., Kossoy, A. D., ANAL. CHEM. 33,1437 (1961). 12) \ , Porcaro. P. J.. Johnston, V. D . , Zbid., 33, 1738 (1961): WILLIAM J. HOULIHAN
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East Rutherford, N. J.
