Spectroscopic Determination of Cysteine with Alizarin Red S and Copper

Abstract

ABSTRACT The interaction between metal complex Cu2+–ARS (Alizarin Red S) and l-cysteine was investigated via fluorescence and absorption spectroscopies. In pH 5.2 Britton–Robinson buffer, the addition of L-cysteine into Cu2+–ARS system resulted in a fluorescence enhancement because cysteine reduced Cu2+ to Cu+, which led to Cu2+–ARS decompound, and ARS was released. The result was also supported by absorption spectroscopy change. A good linear response of fluorescence intensity as a function of cysteine concentration was obtained ranging from 1.0 × 10−6 to 4.0 × 10−5 mol L−1 with the detection limit as 1.08 × 10−7 mol L−1. The introduced method has high selectivity over other amino acids such as cystine, tyrosine, tryptophan, methionine, and glycine. It was applied to determine cysteine in protein hydrolysate of fresh pig blood with recovery of 88.4–100.2%.