Analysis of α-Lipoic Acid in Drug Formulations and Dietary Supplement Preparations

A simple and reliable TLC method for analysis of -lipoic acid ( LA) with post-chromatographic derivatisation with palladium(II) chloride immersion reagent has been developed and evaluated. Separation of LA was performed on 20 cm x 10 cm RPTLC plates with 2-propanol-methanol-acetone-water-acetic acid 6: 4: 2: 8: 0.2 (v/v) as mobile phase. Yellow complexes formed in situ were scanned at 375 nm. The migration distance of LA was 43.0 mm. The relationship between peak area and amount of LA applied was evaluated by use of linear (1.0-3.0 mu g per band) and second-degree polynomial ( 0.5-5.0 mu g per band) regression functions. The correlation coefficient (r = 0.999), the limit of quantification (0.39 mu g per band), recovery (98.5-105.2%), and precision (1.8-2.9%) obtained by use of the procedure were satisfactory. The method was used for analysis of LA in several drug formulations and selected dietary supplement preparations. The LA content was 99.5-101.0% in the drug formulations, 98.8-99.5% in three of five dietary supplements tested, and 48.0-185.0% in two other dietary supplements.