GAS-LIqUID CHROMATOGRAPHY AND THE PERFUMER and camphor is indicative of the degree of change which must be anticipated. Unfortunately, available stationary phases fall mainly into a few well- defined groups. Polarity differences between group and group are rather great, while differences between the members of any one group may prove too small to be effective. Lastly, I would like to suggest the third very simple method of running (b) Figure 4 Showing the effect of temperature on resolution of linalol and camphor on p.p.s. At 110% camphor appears as a "shoulder" on the leading edge of the linalol peak.

378 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS successive chromatograms on the same polar stationary phase at varying temperatures. I believe that many workers with essential oils choose column temperatures too high for adequate resolution of any but the least volatile components. (Some published chromatograms have even shown clear evidence of partial thermal decomposition, indicated by a general lift of the base-line.) This predilection for high temperatures, perhaps due to impatience, may well explain why the magnitude of the effect which I propose to describe seems hitherto to have been overlooked. At 120 ø C and above, the first-eluted fractions of essential oils tend to produce an unsightly jumble of concurrent peaks. Good resolution is hardly possible until the column temperature is dropped below 100 ø C. During a study of the early fractions of oils of lavendin on p.p.s. at 70 ø C, I observed a peak where no peak had occurred in chromatograms at 100 ø C. It proved to be camphor, which overlaps with linalol at 100 ø C and more. It was easy to demonstrate the increasing separation of camphor from linalol with successive reductions of temperature (Fig. 4). Another chromatogram of oil of geranium on p.p.s. at 70 ø C (Fig. $) revealed a clear separation of linalol from isomenthone, which is not possible on the same column at 100 ø C (Fig. 2). Figure • Separation of linalol from isomenthone by reduction of column temperature (see also Fig. •a). Peak resolution* for linalol-camphor was 0 at 120 ø C, 1.4 at 90 ø C and 8-9 at 70 ø C. For linalol-isomenthone, the figures were 0 at 100 ø C and *Expressed as twice the difference between retention times, divided by the sum of the two peak widths, measured in time units.