Enantiomeric Determination Of Alpha-Lipoic Acid In Dietary Supplements By Liquid Chromatography/Mass Spectrometry

An LC/MS method with high sensitivity and selectivity was developed for the chiral separation and quantification of alpha-lipoic acid in dietary supplements. Excellent mutual separation of the optical isomers of alpha-lipoic acid was achieved by using CHIRALPAK AD-RH as a chiral column. Solid-phase extraction after liquid-liquid extraction resulted in sufficient purification of the sample matrix, which in turn improved quantification. The LOD and LOQ of the proposed method were 5 ng/mL and 10 ng/mL, respectively. Enantiomeric analysis of alpha-lipoic acid in commercially available dietary supplements revealed the presence of some unknown enantiomers in the samples. The d-enantiomer may have been converted into the l-enantiomer during the manufacturing process. The developed method can be used to measure the optical isomers of alpha-lipoic acid in dietary supplements, and is expected to be useful for the quality evaluation of a product.