Validated method for determination of α-lipoic acid in dietary supplement tablets by reversed phase liquid chromatography

A rapid high performance liquid chromatographic method was developed and validated for the determination of alpha-lipoic acid in pharmaceutical dosage forms. The analysis was performed using a reversed phase Supelcosil LC-18 (150 x 4 mm, 3 mum) column. The mobile phase consisted of acetonitrile : 0.05 M potassium mono-phosphate, pH 2.5 (45 : 55 v/v) at a flow rate of 0.8 mL/min. The UV-detector was set at 332 nm. The developed method showed a good linear relationship in the concentration range from 10-500 mug/mL with a correlation coefficient from 0.9999. The limit of detection and limit of quantification were 4.4 and 16.8 mug/mL, respectively. These values are high due to the low absorption coefficient of pure lipoic acid (epsilon = 150) at 332 nm. Statistical analysis proves that the method is reproducible.