Determination of cysteine in human plasma by high-performance liquid chromatography and ultraviolet detection after pre-column derivatization with 2-chloro-1-methylpyridinium iodide

This paper describes the development and validation of a reversed-phase HPL C method with isocratic conditions for the analysis of total cysteine in hu man plasma. The essential steps in the assay include derivatization of cyst eine via thiol group with 2-chloro-1-methylpyridinium iodide (CMPI), separa tion of the formed cysteine S-pyridinium derivative from endogenous thiol d erivatives, usually present in biological samples, by ion-pair reversed-pha se HPLC, and ultraviolet detection. Free cystine and protein-bound cysteine are converted to their reduced counterpart by the use of 2-mercaptoethanol . The standard curve is linear over the concentration range from 20 to 300 nmol ml(-1). The recoveries are from 93.9 to 105.90% and imprecision was at most 2.5%. Optimal conditions are determined for all steps of the analytic al procedure. (C) 2000 Elsevier Science B.V. All rights reserved.