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An isocratic reversed phase high-performance liquid chromatography coupled with a photo diode array and electrospray ionization tandem mass spectrometry (LC-PDA-ESI-MS/MS) method was developed for the identification and characterization of stress degradation products (DPs) and an unknown process related impurity (PR) of rivaroxaban (RVR) in bulk drugs. RVR, a selective and direct factor Xa inhibitor, was subjected to hydrolysis (acidic, alkaline and neutral), photolysis, thermolysis, and oxidation as per ICH guidelines and found susceptible to acid and base hydrolytic stress conditions. In total, three DPs (DP-1, DP-2, and DP-3) were formed. All the DPs, PR and RVR were well separated on a Kinetex C 18 (150 Â 4.6 mm, 5 mm) column using a mobile phase consisting of 20 mM ammonium acetate and acetonitrile (65 : 35 v/v) at a flow rate of 1.0 ml min À1 . To elucidate the structures of PR and DPs, MS/MS experiments were carried out to study the molecular ion fragmentation of RVR, PR, and DPs. The product ions of PR and DPs were compared with those of the RVR molecular ion to assign most possible structures. Potential impurities were isolated by semi-preparative HPLC and subjected to NMR spectroscopy. The LC-PDA method was validated with respect to specificity, linearity, accuracy, precision and robustness as per ICH guidelines.

The current study reports the characterization of degradation products of ambrisentan by liquid chromatography-tandem mass spectrometry, and development and validation of a stability-indicating reversed phase high performance liquid chromatographic method for determination of ambrisentan in the presence of its process related impurities in bulk drugs. The drug was subjected to various stress conditions such as hydrolysis, oxidation, photo-and thermal degradations to investigate the stabilityindicating ability of the method. Significant degradation was observed during acidic and oxidative stresses. Ambrisentan was well resolved from its process related impurities and degradation products formed under stress conditions. The chromatographic separation was accomplished on an Agilent XDB C 18 column (150 Â 4.6 mm; 5 mm) with the mobile phase consisting of 10 mM NH 4 OAc (pH = 5.2) and CH 3 CN in a gradient elution mode at a flow rate of 1.0 ml min À1 . The eluents were monitored by a photodiode array detector at 215 nm and quantitation limits were obtained in the range of 0.07-0.25 mg ml À1 for ambrisentan and all its process related impurities. The developed liquid chromatographic method was validated with respect to accuracy, precision, linearity, robustness and limits of detection and quantitation. The degradation products were characterized by comparing their collision induced dissociation mass spectral data with that of ambrisentan and the most possible degradation and fragmentation pathways were proposed.

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