Spectrophotometric determination of thioctic acid in its dosage forms through complex formation with Pd(II)

A simple and sensitive spectrophotometric method has been developed for the determination of thioctic acid in pharmaceutical preparations. The proposed method is based upon the formation of a complex with palladium(II) in acetate buffer of pH 4.8 with an absorption maximum at 318 nm. The absorbance obeyed Beer's law over the range of 2-20 mu g mL(-1) with a minimum detection limit of 0.15 mu g mL(-1) and molar absorptivity (zeta) of 7 x 10(3) L mol(-1).cm(-1). The different experimental parameters affecting the development and stability of the color were carefully studied and optimized. The proposed method was successfully applied to the analysis of commercial tablets and ampoules. The results obtained were in good agreement with those obtained using a reference spectrophotometric method. A proposal of the reaction pathway is presented.