A RELATIVELY SIMPLE TEST FOR THE DIRECT DETERMINATION OF THE CYSTEINECONTENT IN PHOTOGRAPHIC GELATIN USING A THIOL-SPECIFIC FLUOROGENIC REAGENT

This report describes the development and validation of a direct measu rement of cysteine in photographic gelatin using a fluorogenic reagent , ammonium 7-fluoro-2,1,3-benzoxadiazole 4-sulphonate (SBD-F). This un ique analytical approach greatly simplifies the measurement of cystein e without sacrificing the quality of the information obtained. No comp licated acid hydrolysis or difficult high-performance liquid chromatog raphic separations are required. SBD-F is water soluble and thiol spec ific. SBD-F has many excellent features which allow direct labeling of the cysteine thiol in gelatin solutions under controlled laboratory c onditions. At pH 8.0 the reaction kinetics are complete in 1 hour at 6 0 degrees C. Additionally, the probe is not naturally fluorescent and thus no separation step is required for removal of unbound reagent. Th e analytical test is both simple and rapid. This method allows determi nation of cysteine by fluorescence emission in less than 2 hours.