Determination of lipoic acid in human plasma by high-performance liquid chromatography with electrochemical detection

A selective and sensitive method for the determination of lipoic acid in human plasma samples has been developed. After enzymatic hydrolysis of the sample, the liberated lipoic acid was extracted by a solid-phase cartridge and measured by HPLC using electrochemical detection. The detection limit was 1 ng/ml lipoic acid in plasma. The calibration curve was non-linear in the range 0.01-50 microgram/ml but could be described by a power function. The average extraction recoveries were 82.5 and 85.1% at the 25 and 2500 ng/ml levels, respectively. Coefficients of variation for both within-day and day-to-day analysis were between 2.1 and 9.4%. The assay method is sensitive, reproducible and suitable for disposition studies of lipoic acid in humans.