Spectrophotometric determination of thioctic (α-lipoic) acid in water and pharmaceutical preparations

A spectrophotometric method is described for the assay of thioctic acid. The method is based on the reaction between the drug and palladium(II) chloride. In this reaction, a yellow-coloured, water soluble product with a 1:1 stoichiometric ra- tio and an absorption maximum at 365 nm was formed. The stability of the formed complex depends on various factors (pH, reaction time, concentration of reagents, ionic strength). Based on these findings, a new method is suggested for the spectro- photometric determination of thioctic acid in pharmaceutical formulations. This method is simple, sensitive and reproducible.