Capillary gas chromatographic analysis of human skin surface lipids after microsampling on ground-glass platelets

Small amounts of human skin surface lipids, in the 1-20 micrograms range, sampled on ground-glass platelets are investigated using capillary gas chromatography. A first system allows the separation of the neutral lipids, up to the triglyceride fraction. A second system reveals the distribution of the free fatty acids or of the free + glyceride fatty acids, after a methylation or transesterification step. Examination of samples from nine subjects shows that the unsaturation of the free fatty acids increases during a four-day period of accumulation. Comparison of the free fatty acid fraction and the free + glyceride fatty acid fraction shows that the fraction is more saturated than the latter. It is concluded that the bacterial lipases which cleave the fatty acids from the ester bond favor the liberation of straight-chain saturated fatty acids from sebum triglycerides. This result is confirmed by comparison of the free fatty acid fraction with the glyceride fatty acid fraction separated from bulk samples of skin surface lipids from hair and scalp.