STUDIES ON PHOTOISOMERIZATION OF 4,4'-DIAMINOSTILBENE-2,2'-DISULFONIC ACID FOR QUALITY ASSURANCE BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

Studies on the photoisomerization of 4,4'-diaminostilbene-2,2'-disulphonic acid (DAST) were carried out using controlled light at 350 nm to follow the E to Z isomerization and to develop a simple and rapid stability-indicating assay using high-performance liquid chromatography. Photoisomers and process impurities, viz., 4.4'-diaminodibenzyl-2,2'-disulphonic acid and 4,4'-dinitrostilbene-2,2'-disulphonic acid, were separated using a reversed-phase C18 column, an eluent containing aqueous ammonium sulphate and 2-propanol and a variable-wavelength UV spectrophotometric detector at 245 and 338 nm. The method was used for quality assurance and validated using several lots of industrial samples. The mean recovery of DAST from authentic samples was 99.75 +/- 1.17%.