Quantitative analysis of N-acetylcysteine and its pharmacopeial impuritiesin a pharmaceutical formulation by liquid chromatography-UV detection-massspectrometry

A new method for the simultaneous determination of N-acetylcysteine and its pharmacopeial impurities, cysteine, cystine, N,N'-diacetylcystine and N,S- diacetylcysteine in an effervescent tablet has been developed. The method i s based on on-line LC-UV-MS using a pneumatically-assisted electrospray int erface (ionspray). The stability of the thiol moieties of the analytes was ensured by the acidic pH of the LC mobile phase. Quantitation of N-acetylcy steine was performed with UV detection to avoid ion-source overloading effe ct due to its higher concentration, whereas the impurities could be easily separated and quantified in MS. The method was validated in terms of stabil ity, linearity, precision and accuracy. (C) 2000 Elsevier Science B.V. All rights reserved.