DETERMINATION OF THE CYSTEINE DERIVATIVES N-ACETYLCYSTEINE, S-CARBOXYMETHYLCYSTEINE AND METHYLCYSTEINE IN PHARMACEUTICALS BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

A high-performance liquid chromatographic method was developed for the determination of three mucolytic agents, N-acetylcysteine (NAGS), S-carboxymethylcysteine (SCMCS) and methylcysteine (MCS). Chromatography was performed on an ODS column using an isocratic mobile phase consisting of acetonitrile, methanol and sodium hexanesulfonic acid buffer (pH 2.9) at a flow-rate of 1.0 ml/min, with UV detection at 220 nm. Methionine was used as an internal standard. Good quantitative results were obtained, the recoveries from synthetic mixtures being >98.2% with R.S.D. <1%. Linearity over a concentration range of over one order magnitude was obtained; the correlation coefficients were >0.9997 at concentrations of 0.05, 0.1, 1.0, 2.0 and 3.0 mg/ml. The addition of methanol and acetonitrile to the mobile phase improved the peak shape and retention of the compounds of interest. The selectivity of the method was demonstrated by separating four similar thiol compounds and determination of the analytes in pharmaceuticals.