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-c arboxymethylcysteine (SCMCS) and methylcysteine (MCS). Chromatography was performed on an ODS column using an isocratic mobile phase consist ing of acetonitrile, methanol and sodium hexanesulfonic acid buffer (p H 2.9) at a flow-rate of 1.0 ml/min, with UV detection at 220 nm. Meth ionine was used as an internal standard. Good quantitative results wer e obtained, the recoveries from synthetic mixtures being >98.2% with R .S.D. <1%. Linearity over a concentration range of over one order magn itude was obtained; the correlation coefficients were >0.9997 at conce ntrations of 0.05, 0.1, 1.0, 2.0 and 3.0 mg/ml. The addition of methan ol and acetonitrile to the mobile phase improved the peak shape and re tention of the compounds of interest. The selectivity of the method wa s demonstrated by separating four similar thiol compounds and determin ation of the analytes in pharmaceuticals.