A new and versatile method for determination of thiolamines of biological importance

A method for the separation and quantitation of several important biological thiolamines is described. The procedure employs a C₁₈ reversed-phase HPLC system to separate the dinitrophenyl derivatives of reduced and oxidized glutathione and cysteine and relies on an internal standard, N^ϵ-methyllysine, to minimize experimental error. The method was validated in three matrices (water, HepG2 cell lysates, and mouse liver homogenates) using several criteria. The detector response was linear for the dinitrophenyl derivatives of glutathione, glutathione disulfide, cysteine, and cystine in the concentrations ranging from 10 to 50 nmol/ml. Inter- and intra-day variation, percent recovery in the biological matrices, and limits of detection and quantitation were determined. For the most accurate determination, it is essential that standard curves be produced daily and in the same matrix as that being analyzed.