Liquid chromatographic determination of tolrestat and related compounds in raw materials

A liquid chromatographic method was developed for the determination of tolrestat and 7 related compounds. The lower limit of quantitation of the related compounds in the presence of the drug was <0.05%. The coefficient of variation on the assay of drug raw material analyzed on 5 different days was 0.75%. Total impurities found in 2 samples of tolrestat from different sources were 0.12 and 0.54%, respectively. The method was validated by a second laboratory.