Analysis of unknown compounds in azithromycin bulk samples with liquid chromatography coupled to ion trap mass spectrometry.

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.

Isocratic liquid chromatographic method for the analysis of azithromycin and its structurally related substances in bulk samples.

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.

Liquid chromatography of troleandomycin.

Until now no liquid chromatography (LC) method is described to determine the purity and content of troleandomycin and its related substances. A simple, robust, sensitive and selective isocratic liquid chromatographic method suitable for the determination of the antibiotic troleandomycin and its related substances is described. This method utilizes as a stationary phase: XTerra RP18 5 microm (25 cm x 4.6 mm I.D.) at 30 degrees C and as mobile phase: acetonitrile-0.2 M ammonium acetate buffer (pH 6.0)-water (45:5:50, v/v), delivered at a flow-rate of 1.0 ml/min. UV detection is performed at 205 nm. Troleandomycin is separated from the partially acetylated related substances and from several unknown impurities present in commercial samples. The robustness of the method was evaluated by a full-factorial experimental design.

Investigation of unknown related substances in commercial erythromycin samples with liquid chromatography/mass spectrometry.

A selective reversed phase liquid chromatography/mass spectrometry (LC/MS(n)) method is described for the identification of erythromycin impurities and related substances in commercial erythromycin samples. Mass spectral data are acquired on a LCQ ion trap mass spectrometer equipped with an electrospray interface operated in positive ion mode. The LCQ is ideally suited for identification of impurities and related substances because it provides on-line LC/MS(n) capability. Compared with UV detection, this hyphenated LC/MS(n) technique provides as a main advantage efficient identification of novel substances without time-consuming isolation and purification procedures. Using this method four novel related substances were identified in commercial samples.

Separation of erythromycin and related substances on base-deactivated reversed-phase silica gel columns.

An official liquid chromatographic method for the analysis of erythromycin and related substances, which is based on a polymer reversed-phase, is described in the European Pharmacopoeia and in the United States Pharmacopeia. The pH of the mobile phase used in this system is 9.0. Recent advanced technology has led to the introduction of a new generation of silica-based reversed-phase column packings, which are claimed to be much more stable towards bases. They are useful for the analysis of basic compounds. Studies to verify the separation of erythromycin and related substances on Hypersil BDS C18, Luna C18(2), Inertsil ODS-2 and Supelcosil ABZ+ have been performed and the results are presented. It is shown that these base-deactivated phases give a better sensitivity and selectivity towards erythromycins than the polymer phase, provided that an adapted mobile phase is used. This is the first liquid chromatographic method described for the separation of erythromycin D from erythromycin A.