Spectrofluorimetic determination of cysteine based on the fluorescence inhibition of Cd(II)–8-hydroxyquinoline-5-sulphonic acid complex by cysteine

A spectrofluorimetric method for the determination of cysteine at trace and ultra trace levels (0–1.82×10−5 mol l−1) has been developed. It is based on the efficient inhibition action of cysteine on the fluorescent system of Cd(II)–8-hydroxyquinoline-5-sulphonic acid complex (Cd(II)–HQS) (λex 364.8 nm, λem 510.4 nm) solution at pH 8.5. The method has been applied to protein hydrolysate and cystine electrolyte samples.