FIXED PHASE OR CARRIER IN CHROMATOGRAPHY 101 with cross-sectional area of hair. It was shown that "problem" hair has a higher Trotter Index (nearer a circular shape) than normal hair of the same degree of medullation, and a lower incidence of medullation than normal hair of the same Trotter Index. dcknowledgements: The authors wish to express their appreciation for the skilled assistance of W. F. Munn and Mrs. Elsa Knitl in taking the photomicrographs. REFERENCES (1) Shillaber, C. P., "Photomicrography in Theory and Practice," John Wiley and Sons, Inc., New York (1945). (2) Barnard, J. E., and Welch, F. V., "Practical Photomicrography," Arnold Publishers, London (1936). (3) Wildman, A. B., "The Microscopy of Animal Textile Fibres," Wool Industries Research Association, Torridon (1954). (4) Heyn, A. N.J., "Fiber Microscopy," Interscience Publishers, Inc., New York (1954). (5) Munn, W. I5'., U.S. Patent No. 2,537,846, January 9, 1951. (6) Munn, W. I5'., Research Comments, 3, No. 1 (1951). (7) Munn, W. I5'., and Evans, R. L., Proc. Sci. Sect. Toilet Goods aissoc., May (1952). (8) Munn, W. I5'., Exakta, 2, 2, 6 (1953). (9) Trotter, M., and Duggins, 0. H., aim. 5•. Phys. ainthropoL, 6, 489 (1948). (10) Mercer, E. H., Textile Research pc., 23, 388 (1953). (! 1) Horio, M., and Kondo, T., Ibid., 23, 373 (1953). (12) Dusenbury, J. H., and Jeffries,•,., •7. Soci Cosmetic Chem., 6, 355 (1955). (13) Duggins, O. H., and Trotter, M, aim. 5•. Phys. ainthropoL, 8, 399 (1950). SOME REMARKS ON THE NATURE OF THE FIXED PHASE OR O F THE CARRIER IN GAS-LI QUID PARTI- TION CHROMATOGRAPHY OF ESSENTIAL OILS AND AROMATICS* By YvEs-RENf• N^vEs, D.Sc. L. Givaudan and Co., Ltd., Vernier, Geneva, Switzerland WE s•ovI.•) on no account neglect or underrate the fact that the constituents of essential oils or aromatics may be altered on contact with the fixed phase or the carrier in gas-liquid partition chromatography. Most of the constituents of the essential oils and most of the aromatics have to be examined by gas-liquid partition chromatography at relatively high temperatures because of the prerequisites for the functioning of the usual detectors. Substances used for the fixed phase or as carriers which are appropriate for the analysis of less fragile substances or at lower temperatures are quite unsuitable here. It is considered necessary to mention these facts because some workers appear to be unaware of them, and others underrate their importance. It is essential that an analytical technique, whose use can be invaluable * Presented at the August 2, 1957, Meeting, Geneva, Switzerland.

102 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS particularly to the aromatic and cosmetic industries, should not suffer from fundamental neglect. In order to carry out gas-liquid partition chromatography efficiently, we have to bear in mind the fact that the principal constituents of essential oils and almost all aromatics are polar substances, and that most of them are able to form associations by means of hydrogen bonds. Therefore, analogous substances are to be preferred for the fixed phase. Even if it is possible to work at pressures going as low as 40 cm. of mer- cury at the inlet and 10 cm. at the outlet, by using sufficiently sensitive catbarometers, the working temperature should lie between 120 ø and 220 ø. This limits considerably the choice of the fixed phase. At such temperatures, most of the heavy substances generally used in gas-liquid partition chromatography have to be removed. Thus the n- octyl, n-nonyl, isodecyl and tetrahydrofurfuryl phthalates are no longer suitable above 150-170 ø, nor are octadecyl stearate or orthocresyl phos- phate at slightly higher temperatures. The safety margin for using these products is still further lowered by the use of certain carriers. Certain polyethylene glycols or polypropylene glycols having a mo- lecular weight between 800 and 1000 or their esters (e.g., polyethylene succi- nate), Or their ether derivatives resulting from partial methylation, can be used from 180 ø to 190 ø, and alkyl (or aryl) siloxanes can be used up to 220 ø . At such high temperatures, however, most of these give off gases during the first few hours of use. After six to eight hours this drawback disappears and the columns can be used for a long time. Silicones of diverse origins (Silicone Elastomers DC 123 or DC 152, Silastomers DC 132 and DC 156, Wacker's Silicone gum DC and Apiezon M grease) can be used. It is advantageous first of all to wash some of these products with ethyl acetate. In the case of nonpolar substances, the polythenes of molecular weight 30,000 to 40,000 or perhydrosqualene may be used. The use of ph thalic or succinic esters or of some silicones is to be avoided in the case of easily dehydrated constituents of essential oils or aromatics. The choice of the carrier is also of great importance. Diatomaceous earths lower the temperature at which the esters used as fixed phase are altered, and give rise to dehydration, condensation or other reactions of the constituents under examination. The same thing happens with the powders obtained by crushing refractory bricks (e.g., Sterchamol). Sea sand of the size between sieve 44 and sieve 52 (British standards) is often preferable, in spite of its poor retention of the fixed phase. With glass powders this disadvantage becomes too grea. t• Sodium chloride passing through sieves 30 to 40 can be used, as it retains 5 per cent silicone grease. The reactions which are apt to occur at the resistances in the catharom- eter must not be neglected. Thus dehydrogenation of the alcohols has