ANALYSIS OF LIPOIC ACID IN BIOLOGICAL SAMPLES BY GAS-CHROMATOGRAPHY WITH FLAME PHOTOMETRIC DETECTION

A selective and sensitive gas chromatographic method for the analysis of lipoic acid in biological samples has been developed. After base hy drolysis of the sample, the liberated lipoic acid was converted into i ts S,S-diethoxycarbonyl methyl ester derivative and measured by gas ch romatography using a DB-210 capillary column and a flame photometric d etector. The calibration curve was linear in the range 20-500 ng, and the detection limit was ca. 50 pg injected. The best hydrolysis condit ions for the biological samples were obtained by using 2 M potassium h ydroxide containing 4% bovine serum albumin at 110-degrees-C for 3 h. Using this method, lipoic acid in the hydrolysate could be selectively determined without any interference from matrix substances. Analytica l results for the determination of lipoic acid in the mouse tissue and bacterial cell samples are presented.