Determination of Alpha-Lipoic Acid in a Nutritional Supplement Using High Performance Liquid Chromatography

Alpha lipoic acid has the ability to react and neutralize reactive oxygen species (ROS) such as superoxide radicals, simple oxygen, hydroxyl radicals, hypochlorous acid and peroxyl radicals. A rapid high-performance liquid chromatographic method for determination of lipoic acid in a nutritional supplement was developed. The method involved sample preparation and the mobile phase comprised of 50 mM disodium hydrogen phosphate buffer (pH 2.5 adjusted with 1 M H3PO4): acetonitrile in the ratio of 50:50. The separation was done using a C18 column (150 mm) and detection was carried out using UV detection at 201 nm. The assay was found to be linear in the range of 1.56 - 50 μg/mL with the correlation coefficient of 0.9997. Method precision was determined while LOD was 0.05 μg/mL and LOQ 0.15 μg/mL. The chromatographic peak LA retention time was 6 min.