Abstract: A method to determine the composition of fatty acids in Styrax tonkinesis seed oil, kernel and seed shell was developed by on-line methylation and gas chromatography using a vertical microfurnace pyrolyzer. On-line methylation of S.tonkinesis samples at 350 ℃ in the presence of trimethylsulfonium hydroxide (TMSH) allowed analysis of fatty acids as their corresponding methyl derivatives. The main fatty acids were palmitic acid (C_16:0), stearic acid (C_18:0), oleic acid (C_18:1), linoleic acid (C_18:2) and linolenic acid (C_18:3). The content of unsaturated fatty acid was more than 84.5% and the highest linoleic acid content was up to 47.29%. At the optimum conditions, the RSDs of the fatty acids were less than 3.81% (n=5). Furthermore, the composition of fatty acids in the samples from different growing places and different edible oil species was compared by similarity matrix. The results show roughly the same fatty acid composition of the S. tonkinesis from different growing places. It is most close to the corn oil, and the similarity is between 0.987-0.990. The content of unsaturated fatty acids (C_18:2 and C_18:3) in S. tonkinesis is close to soybean oil and sunflower seed oil, but higher than general vegetable oil. This can prove that it has high nutritional value. The on-line methylation gas chromatography is a simple, rapid and accurate method for the determination of the composition of fatty acids in S. tonkinesis.

Key words: gas chromatography, on-line methylation, similarity, Styrax tonkinesis seed oil, fatty acids