Multidimensional narrow bore liquid chromatography analysis of Ro 24-0238 in human plasma

A highly sensitive LC method has been developed and validated for quantitation of Ro 24-0238 in human plasma using Ro 24-2446 as an internal standard. With 1 ml of plasma, the limit of quantitation of the method was 50 pg ml-1 of Ro 24-0238. After solid-phase extraction with C18 reversed-phase cartridges, the samples were reconstituted in an acidic buffer solution; under these conditions, Ro 24-0238 and Ro 24-2446 (IS) were converted to their cationic forms. The LC system employed a strong cation exchange column and a narrow bore reversed-phase column, connected via a column switching valve. The cationic analyte and internal standard were separated from most of the endogenous components of plasma on the cation exchange column. A small fraction containing the analyte and the internal standard was transferred by automated valve switching to the narrow bore reversed-phase column, which further resolved the individual components. The chromatography was monitored by UV absorption at 322 nm. The overall intra-assay precision was 3.6% (RSD) and the per cent error was less than +/- 11%. The overall inter-assay precision was 3.9% (RSD). Linearity was demonstrated in a concentration range of 50-5000 pg ml-1. This method has been applied to pharmacokinetic studies of Ro 24-0238 in man.