Determination of free α-lipoic acid in foodstuffs by HPLC coupled with CEAD and ESI-MS

A simple and rapid method for determination of free α-lipoic acid in different food matrices has been developed. It consists of extraction of α-lipoic acid with 0.5% glacial acetic acid in methanol by sonication, quantitative analysis of the extract by isocratic RP-HPLC (acetonitrile/methanol/50 mM potassium dihydrogen phosphate buffer adjusted to pH 3 with phosphoric acid: 350/65/585, v:v:v) at a flow rate of 0.45 ml/min coupled with coulometric electrode array detection at potentials between +300 and +700 mV and qualitative analysis by LC–ESI-MS in the negative ion mode for confirmation. Egg, dried egg powder, mayonnaise, fine peas and potatoes were analysed and free α-lipoic acid contents ranged from 0.1 to 4.2 μg/g with recoveries between 70% and 94%. Limits of quantitation were between 0.1 and 0.3 μg/g. This newly developed method can be used to establish a database for the content of free α-lipoic acid in different foodstuffs.