IDENTIFICATION OF SURFACE ACTIVE AGENTS 787 product provides additional criteria for identification. This may be done easily by first analyzing a sample of the surface active agent in pyridine. Then the two reagents can be added and the chromatogram of the trimethylsilylated derivatives run next. EXPERIMENTAL Preparation of Derivatives About 50-100 mg. of surface active agent is dissolved in 1 ml. of anhy- drous pyridine (kept over KOH pellets) in a small plastic stoppered vial, and 0.2 ml. of hexamethyldisilazane and 0.1 ml. of trimethylchlorosilane are then added. The mixture is shaken vigorously for 30 seconds and then allowed to stand for 5 minutes. The solutions become cloudy, and a precipitate of ammonium chloride is formed. It is not necessary to remove this precipitate. The supernatant liquid may be run directly by gas chromatography (14). Gas Chromatography An F&M Model 810 Gas Chromatograph with thermal conductivity detector was used. All of the chromatograms were run using identical conditions. A 3 ft. by 0.125 in. o.d. column packed with •% SE-52 silicone gum rubber on Anakrom A was employed. The helium flow rate was 20 mi./minute, and the column temperature was programmed from 100 to 300øC at a rate of 20øC/minute. One-microliter samples were injected into the gas chromatograph, using a Hamilton 10 microliter syringe. RESULTS AND DISCUSSION Figure 1 shows a comprison of the chromatograms obtained from glyceryl monostearate before and after trimethylsilylation. The top chromatogram was obtained from a solution of glyceryl monostearate in pyridine. It is apparent that very little information can be obtained from this. The high boiling point and polar character of these com- ponents show very pronounced tailing for those peaks that have passed through the column. The bottom chromatogram shows the results ob- tained for the glyceryl monostearate derivatives after trimethylsilyla- tion. The significant improvement is apparent. All of the major peaks have been identified. Peak A is glycerin, and Peaks B and C are glyceryl mono-esters of palmitic and stearic acids, respectively. The small peak in front of peak B is due to glyceryl

788 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS SORBITAN MONOLAURATE I l RETENTION TIME (Minutes) 5 I• 15 20 Figure 4. Top: Sorbitan monolaurate in pyridine Bottom: Sorbitan monolaurate after trimethylsilylation monomyristate. The composition of the monoesters is indicative of the fatty acid composition of the glyceryl ester. Peaks D, E, and F are di- ester peaks. Peak D is the dipalmitate peak F is the distearate. The peak between these is due to the mixed ester of palmitic and stearic acids. These three peaks have been found to be in the expected ratio for the random combination of stearic and palmitic acids with glycerin. This