Study on the flow injection method for the determination of L-cysteine with a Cu(II) complex by fluorescence quenching

Abstract

1344-1347A flow injection method for fluorescence determination of cysteine using 5-(3-fluo-4-chloropheny lazo)-8-benzenesulfonamidoquinoline (FCPBSQ), a new fluorescence reagent, has been proposed. The method is based on the quenching of fluorescence in the Cu(II)-FCPBSQ system by cysteine in nearly neutral medium. Under the optimum conditions, the fluorescence quenching intensity increases linearly with increase in the concentration of cysteine in the range of 0.050-6.0 μg/ml. The detection limits of this method is 0.010 μg/ml with a sample frequency of 64h-1. The method is free of interference from several metal ions and amino acids without -SH group and has been successfully applied for the determination of cysteine in the pharmachemical samples. The mechanism of the fluorescence quenching is also discussed