Determination of Clorsulon and its related substances in commercial bulk drug substance batches by a rapid ion-pair UPLC method.

Clorsulon is a potent anthelmintic agent and is widely used for the treatment and control of parasites including adult liver flukes in cattle and sheep. A rapid ion-paired reversed phase ultraperformance liquid chromatography (IP-UPLC) method has been developed and validated for determination of Clorsulon and its related substances in bulk drug substance batches of Clorsulon with a short octadecyl column. Analytes were eluted by a gradient elution on a Acquity UPLC® BEH C18 column (50 mm × 2.1 mm i.d., 1.7 µm particle size). Column temperature was maintained at 55 °C and all analytes were monitored by UV detection at 268 nm. Mobile phase-A constitutes 3 mM tetrabutylammonium hydroxide in H2O and mobile phase-B constitutes acetonitrile/methanol (50/50, v/v), respectively. All analytes of interest were adequately separated within 5 min. The analytes were quantitated against an external reference standard of Clorsulon. The chemical structures of degradation products of Clorsulon were proposed based on two-dimensional UPLC-MS data. The IP-UPLC method has been successfully validated and demonstrated to be accurate, sensitive, robust, and specific.