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A selective reversed-phase liquid chromatography/mass spectrometry (LC/MS(n)) method is described for the identification of azithromycin impurities and related substances in commercial azithromycin samples. Mass spectral data are acquired on an LCQ ion trap mass spectrometer equipped with an atmospheric pressure chemical ionization interface operated in positive ion mode. The LCQ provides on-line LC/MS(n) capability, making it ideally suited for identification purposes. In comparison with UV detection, this hyphenated technique provides as its main advantage efficient identification of novel substances without time-consuming isolation and purification procedures. Using this technique, six novel related substances detected in commercial azithromycin samples have been studied., (Copyright 2003 John Wiley & Sons, Ltd.)

An isocratic liquid chromatographic method with UV detection at 215 nm, which is suitable for the analysis of azithromycin (AZT) in bulk samples, is described. AZT is separated from its synthesis intermediates and a degradation product as well as from six unknown impurities on an XTerra RP18 column at 70 degrees C using a mobile phase consisting of acetonitrile-pH 6.5 0.2M K2HPO4-water (35:10:55, v/v/v) at 1.0 mL/min. The XTerra stationary phase contains methyl groups that are incorporated in the bulk structure of the material. This allows for special selectivities. Robustness is evaluated by a full factorial design experiment. The method shows good selectivity, repeatability, linearity, and sensitivity.