HPLC Determination of α-Lipoic Acid in Health-Care Food

A method of HPLC for determination of α-lipoic acid in health-care food was proposed. The sample was extracted ultrasonically with a mixture of acetonitrile and H2O (4+6, adjusted to pH 3.5) for 25 min. C18 chromatographic column was used as stationary phase, and the above mentioned mixture of acetonitrile and water was used as mobile phase. UV-detection at 210 nm was adopted in the determination. Linear relationship between values of peak area and mass concentration of α-lipoic acid was kept in the range of 20.0-500 mg·L-1, with detection limit (3S/N) and lower limit of determination (10S/N) of 0.86 mg·L-1 and 2.7 mg·L-1 respectively. On the base of a blank sample, test for recovery was made by standard addition method; values of recovery found were in the range of 91.5%-98.7% with RSD′s (n=5) less than 5.0%.