JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS oil of spearmint. Fig. 7 illustrates the use of isobutyl benzoate to determine linalol in oil of rosewood in the presence of four other alcohols (marked by arrows) which contribute considerably towards the figure for apparent linalol content as determined by chemical methods. Detector responses to different compounds will vary, so that for accurate work, preliminary calibrations are necessary. Preparative-scale gas-liquid chromatography is of great assistance in isolating the pure components needed for calibration purposes. Most gas-liquid chromatography equipment is designed to give differ- ential chromatograms, in which the deflection of the pen is a function of the concentration of eluted material in the detector at any given time. In order to compare total amounts of selected component and internal standard, it is necessary to determine their respective peak areas. This is a source of inaccuracy which may be eliminated by the use of integral chromato- grams, in which the deflection of the pen varies with the total amount of material which has entered the detector up to that time. Integrams consist of a series of consecutive steps, each step representing an eluted compound by a sigmoid curve whose total height is a function of the amount eluted. In order to increase the accuracy of height measurements it is convenient to amplify the signal while fitting the recorder with a limit switch which converts the step into a series of beats, thereby increasing the total vertical path of the pen while still keeping the recording within the confines of the chart. Figs. 8 and 0 illustrate how citral-a and citral-b may each be determined in an oil of lemongrass. Fig. 8 shows a differential chromatogram of this -- 0II Figure 8 Chromatogram of oil of lemongrass in the neighbourhood of the citral peaks. (Column temperature 100 ¸ C.)

GAS-LIQUID CHROMATOGRAPHY AND THE PERFUMER 383 OIL OF Figure O (a) Integrams of oil of lemongrass in the neighbourhood of the citral peaks, xvith isopropyl benzoate added as internal standard.--Low magnification. (Column temperature 100øC.) ß t