title: Spectrofluorimetric flow injection method for the individual and successive determination of L-cysteine and L-cystine in pharmaceutical and urine samples.
abstract: A flow injection configuration is proposed for the determination of L-cysteine and L-cystine individually and for mixtures of both analytes. The procedure is based on the rapid oxidation of L-cysteine by thallium(III) with concomitant formation of fluorescent thallium(I). The inclusion of a selecting valve and of a copper-coated cadmium column in the configuration allows the successive determination of two analytes. Linear calibration graphs were obtained between 5 x 10(-6) and 5 x 10(-5) mol dm-3 of L-cysteine and between 2 x 10(-6) and 2 x 10(-5) mol dm-3 of L-cystine. The applicability of the method to the determination of L-cysteine and L-cystine in pharmaceutical preparations was demonstrated by investigating the effect of potential interferents and by the analysis of commercial preparations. The method was successfully applied to the determination of L-cysteine and L-cystine in urine samples.
authors.affiliation: Department of Analytical Chemistry, University of Murcia, Spain.
authors.forename: T
authors.initials: T
authors.lastname: Pérez-Ruiz
authors.forename: C
authors.initials: C
authors.lastname: Martínez-Lozano
authors.forename: V
authors.initials: V
authors.lastname: Tomás
authors.forename: J
authors.initials: J
authors.lastname: Carpena
mesh_terms: D003545:Cysteine / Q000652:urine*; D003555:Cystinuria / Q000652:urine*; D017022:Flow Injection Analysis; D006801:Humans; D007202:Indicators and Reagents; D013050:Spectrometry, Fluorescence
chemical_list: D007202:Indicators and Reagents; D003545:Cysteine