Development and optimization of a rapid HPLC method for analysis of ricobendazole and albendazole sulfone in sheep plasma

A simple, rapid and reliable high performance liquid chromatographic (HPLC) method has been developed and validated for simultaneous determination of ricobendazole (RBZ) and its main metabolite albendazole sulfone (ABZSO2) in sheep plasma using an isocratic system with UV detection. The method involved solid phase extraction followed by separation on a reversed phase C-18 column. Internal standard was selected by quantitative structure retention relationships (QSRRs) analysis. A method to optimize the composition of ternary components mobile phase with the assistance of multiple linear regression is described. Retention times were within 10 min. The calibration curves were linear over a concentration range of 10-1000 ng/ml for both RBZ and ABZSO2 (r > 0.999). Intra-day relative standard deviation at low, medium and high concentration levels were <5.5% for RBZ and <4.6% for ABZSO2; average accuracies were 98.3, 101.0 and 100.5% for RBZ and 101.0, 102.4 and 100.8% for ABZSO2. The inter-day variations at the same concentrations were <5.9% for RBZ and <6.4% for ABZSO2. The extraction recoveries at these concentrations for RBZ, ABZSO2 and the internal standard were all over 96%. The limit of detection and limit of quantitation were 2.4 and 7.1 ng/ml, respectively for RBZ, and 10 ng/ml for both analytes.