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

Abstract

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-colored, water soluble product with a 1:1 stoichiometric ratio 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 spectrophotometric determination of thioctic acid in pharmaceutical formulations. This method is simple, sensitive and reproducible.

Opisana je jednostavna spektrofotometrijska metoda za brzo i tačno određivanje tioktinske kiseline u vodi, injekcionim rastvorima i tabletama. Spektrofotometrijska merenja su izvođena u Britton-Robinson-ovim puferima pri različitim pH vrednostima (2,00-6,00) i konstantnoj jonskoj sili. Sastav, konstanta stabilnosti, molarna apsorptivnost kompleksa su određene različitim metodama. Utvrđen je 1:1 sastav nagrađenog kompleksa i molarna apsorptivnost 4.2x103 l mol-1 cm-1. Relativna standardna devijacija iznosi od 3,10 do 3,76%,{to odgovara propisanim analitičkim standardima.