Ion-chromatographic determination of carbocisteine in pharmaceuticals based on non-suppressed conductimetric detection

A novel method for the determination of carbocisteine (S-CMC), a mucolytic and expectorant drug with an acidic amino acid structure, was developed and validated, using non-suppressed ion-chromatographic system with conductimetric detection, and anion or cation exchange columns. Among the various combinations of column type and eluent composition tested, a cation exchange column with a 0.25 mM trifluoroacetic acid (TFA) as eluent in isocratic mode at 1.2 ml/min gave the best results. S-CMC was very well separated from all common amino acids (resolution>2.6). The retention time was 3.5 min and the asymmetry factor 1.1. A linear calibration curve from 17 to 400 μg/ml (r=0.99994), with a detection limit of 0.14 μg (5.6 μg/ml–25 μl injection volume) and a precision of 1.5% R.S.D. (100 μg/ml, n=3) was achieved. The proposed method was applied for the determination of S-CMC content in intensely colored commercial formulations (syrups). No interference from excipients was found and the only pretreatment step was the appropriate dilution with the mobile phase. Recovery from standard additions was ranged from 96.0 to 104.9% and precision (R.S.D., n=3) 1.8–3.6%.