JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Since the complexity of the material to be examined may mean that all the components are not known, may not be separable by any one technique, or may be sensitive to such conditions as high temperature, type of column packing, etc. it is desirable to have a method of chromato- graphy in which such factors are not of prime importance. Certain azo dyes, of which Dispersol Fast Scarlet B. (C.I. Disperse Red 1.11110) has been found to be most suitable, have been shown to have a pronounced effect upon the shape of the chromatographic band of oils when the chromatography was carried out on paper impregnated with the dye, using petroleum ether as the eluting liquid. At certain temperatures, characteristic of the polar group of the com- pound being examined, a sharp increase in the length of the outline of the band per unit area (the Outline/Area Index) was found (2,3,4). All substances are not, of course, chromatographed by petroleum ether, and to overcome this difficulty the experimental material was dissolved in oleic acid which itself gives a single peak at 17.6øC. It was found that characteristic peaks were still obtained, but in many cases these were rather small. The addition of a small amount of a saturated acid to the oleic acid markedly increased the size of the peaks without altering their appearance at characteristic positions along the temperature axis. Although most saturated acids have this effect, palmitic acid gave the most satisfactory results and a solution of 2% palmitic acid in oleic acid (the carrier) was finally used. The use of such a carrier allowed the effects of concentration to be assessed. It was found that each compound had a critical concentration at which the index peak was a maximum. Thus, by making use of both the temperature and concentration effects it was possible to construct a diagram giving classification along the temperature axis and individual compounds along the concentration axis with peak height as a third dimension, and without separating the com- ponents of the mixture. The third parameter, peak height, appears to be related chiefly to surface activity and, to a more limited extent, to concentration. With regard to surface activity, compounds more surface active than oleic acid suppress the carrier peak which remains intact for compounds less surface active, though here again, concentration, within the limits of the critical concentration, appears to play a minor role. Table I gives the temperatures at which peaks are given by the main

BAND SHAPE ON DYED PAPER AS A METHOD OF CHROMATOGRAPHY 5 polar groups likely to be found in oils and fats. Complexity of molecular structure may cause modifications of this simple pattern. If the com- pound is polyfunctional the peak area may lie across the relevant tem- peratures. Isomers may give peaks on opposite sides of the carrier peak. Table I Peak temperatures for various polar groups Group Temperature øC COOH CO OH Peroxides Carrier 15.6 16.9 18.1 18.8 16.4 15.8 (alcohols, enols, phenols) 15.0- 15.3 17.6 Although only a limited number of isomers have been examined, there is evidence that geometric, and sometimes optical, isomers give such an effect. Although there are four peaks for the carboxyl group, all acids do not give all of these some may be only minor peaks, or completely suppressed. Some of these results for particular compounds are shown in Table II. The peaks occur at these positions whether the isomers are examined separately or as a mixture. Table II Effects due to molecular structure Compound Peak temperature Maleic acid Fumaric acid Erythrodihydroxystearic acid Threodihydroxystearic acid Cis 1,2-dihydroxycyclohexane Trans 1,2-dihydroxycyclohexane Triphenylethyleneglycol (racemate) 16.9 only 18.8 only 18.1 only* 16.9 only* 15.8 18.5 15.8 19.5 *Racemates. No indication of peaks due to separate optical isomers. EXPERIMENTAL The full details of the method have been published elsewhere (4), but the essential points are as follows :w Number one quality, 11 cm, circular filter papers were cut to give eight sectors with half length, narrow tongues between each sector, leaving a 1.5 cm disc in the centre. These papers were dyed with a saturated solution of Dispersol Fast