IDENTIFICATION OF SURFACE ACTIVE AGENTS 785 derivative. The high boiling point and high polarity caused by the presence of one or more hydroxyl groups make it impossible to get good results by gas chromatography on the parent substance. Monoglycerides have been analyzed after conversion to allyl esters by a dehydration reaction (12). This method is applicable to glyceryl mono-esters only. Other work has been performed after converting the free hydroxyl groups 5 )0 RETENTION TIME (Mmufe• 2O Figure 2. Top: Diethylene glycol monostearate in pyridine Bottom: Diethylene glycol monostearate after trimethylsilylation to acetates by reaction with acetyl chloride (13). These techniques have given some interesting results, but each one has some serious drawbacks. The conversion to allyl derivatives is very lengthy and applicable only to components with two adjacent hydroxyl groups. The acetate deriva- tive preparation is also a lengthy procedure and gives rise to high boiling products. The research described in this paper has made use of the reaction of hydroxyl groups contained in surface active agents with hexamethyl-

786 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS disilazane and trimethylchlorosilane. The products are volatile tri- methyl silyl ether derivatives which are suitable for gas chromatography. The use of this reaction has received considerable attention in the sugar and carbohydrate field (14, 15). Compounds as high boiling as tetrasac- charides have been analyzed successfully. The reaction is simple and quantitative without any undesirable side reactions. These derivatives are lower boiling than the corresponding acetates and give sharp, well defined peaks on the gas chromatograph. The use RETENTION TIME (M•nutes) c • Figure 3. Top: Ethylene glycol monostearate in pyridine Bottom: Ethylene glycol monostearate after trimethylsilylation of this technique enables one to get a definitive chromatogram for each of the surface active agents investigated. A comparison of the chromato- gram obtained from the initial pyridine solution with that of the reacted