CHEMICAL ANALYSIS IN THE COSMETIC INDUSTRY 259 same time indicate the presence of any unusual materials. The identification and subsequent extraction or determination of these unusual substances will, however, constitute a separate problem to be dealt with after the "basic analysis" has been done. With products which are not strictly competitive or which are outside the analyst's normal field a good deal of preliminary thought and reading may have to be devoted to planning a likely approach. In such cases an adequate patent survey of the subject is often of great assistance. Much of the work of the non-routine analyst consists of research into methods of analysis and the application or modification of general methods to suit particular problems. The determination of individual components of a mixture is usually required at some stage, and new methods and new techniques are constantly being devised to make the process easier and quicker. Chromatography can no longer be described as a new technique and it now has applications in almost all branches of analysis. Paper chromato- graphy is a rapid and useful technique for the separation of certain closely similar materials from a few micrograms of sample. Glycerol can be separated from other polyalcohols in this way, using water-saturated n-butanol as developer and ammoniacal silver nitrate as detector, the zones showing as black spots. The spots can be eluted with water and the glycerol determined by a modification of the periodate oxidation method •. Hexa- chlorophene and other antiseptics, and thioglycollic and thiolactic acids can also be detected by paper chromatography 2, while considerable use of this method has been made for the separation and identification of dyes and colouring matters. An ingenious method of constantly changing the composition of the developer has been described by Franks', who uses paper chromatography for anionic surface-active agents. The examination of mixtures of oils and fats as occur, for instance, in the oil phase of an emulsion has always been a difficult task if the mixture is at all complex. The determination of the usual constants is still a standard procedure of great utility, but it is particularly useful to be able to separate physically at least one fraction of the fats. This is possible by using column chromatography as described by Williamst when all components of the unsaponifiable matter, except hydrocarbons, are absorbed on the column and the hydrocarbons may be recovered quantitatively from the eluate. In many cases this method can be applied to fat mixtures without separating the unsaponifiable matter, though control tests with known mixtures should first be run. The details are as follows: Chromatographic separation of hydrocarbons. Prepare a column (about 8 cm long by 1 cm in diameter) of chromato-

260 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS graphic alumina in the usual way, using a slurry of alumina and petroleum ether (b.pt. 40ø-60 ø C) to form the column and applying gentle suction. The sample (about 0.5-1.0 g) is dissolved in about 30-40 ml petroleum ether (b.pt. 400-60 ø C) and added through the top of the column, wash- ing-in with small portions of petroleum ether. Elute with the same solvent using about 200 ml in all, suck the column dry, transfer the eluate to a tared flask, evaporate the solvent on the steam bath, dry the residue at 60 ø C, cool and weigh. Often it is not practicable to use so much fat for one determination and a semi-micro modification, which has been in use in the author's laboratory for some time, yields results of precision comparable with those obtained by the standard method. In this modification the length of column is 100 mm and the diameter 12 mm, and as little as 0.1-0-2 g fat and a total volume of 60-70 ml solvent may be used. The residue will contain any hydrocarbons natural to the oils and fats used, but these will usually be very small by comparison with added mineral oil or petroleum waxes. A determination of iodine value on the separated hydrocarbons will reveal the presence of squalene. Recently two papers have been published •,• describing the chromato- graphic separation of the components of technical monoglycerides, using silica gel columns. Ion-exchange chromatography is a useful aid to the analyst, particularly in separating nonionic surface-active materials from ionic types. Newburger 7 has described a method for the analysis of shampoos, using Amberlite C45 resin, in which the alkyl sulphates, fatty acids and fatty alkanolamides are separated. The method described involves a lengthy procedure for the purification of the resin in order to prevent high blanks. A method for examining emulsions by passing them through ion-exchange columns has also appeared 8. It would be inappropriate to leave the subject of chromatography without some reference to the newer technique of gas chromatography. By the use of this elegant technique it is possible, using a very small sample, to separate and determine the components of a mixture of homologues, and in many cases results are obtained which are unattainable by any other method. Classical analysis deals very largely in averages. In the examination of essential oils, for instance, alcohols, aldehydes and esters may be separately determined by the usual methods, but the results are usually calculated by using the molecular weight of the predominating member of the group. It is often useful to know' the proportions of the individual compounds present and gas chromatography is so sensitive that it often detects unsus- pected components. If the so-called lauryl alcohol is subiected to gas- liquid chromatography, using a suitable stationary phase, a whole series of