A spectrofluorimetric method for cysteine and glutathione using the fluorescence system of Zn(II)-8-hydroxyquinoline-5-sulphonic acid complex.

The addition of thiol compounds to the fluorescence system of Zn(II)-8-hydroxyquinoline-5-sulphonic acid complex (Zn(II)-HQS) in H3BO3-Na2B4O7 buffer (pH 8.50) solution led to immediate fluorescence inhibition, which was proportional to their amounts. Based on this finding, a novel spectrofluorimetric method for the determination of cysteine (Cys) and reduced glutathione (GSH) has been developed. The detection limits were 17 ng ml(-1) and 0.6 microg ml(-1), respectively. Most amino acids had no interference at high concentrations. The proposed method has been applied to the determination of Cys in protein hydrolysate and cystine electrolyte, and GSH in human blood serum with recoveries of 95.6-104.5%.