A stock standard solution of alpha-lipoic acid (500g/mL) was prepared by accurately weighing 5mg of analyte and dissolving it in a 1:1 (v/v) ratio of acetonitrile: Milli-Q water to 10mL in a volumetric flask and storing it at 4 ◦C. The working solutions were prepared by suitable dilution of the stock standard solutions with the mobile phase.