Determination of diclofenac and its metabolites in plasma and cerebrospinal fluid by high-performance liquid chromatography with electrochemical detection.

A reversed-phase high-performance liquid chromatographic method with electrochemical detection for the quantitation of diclofenac and metabolites in plasma and cerebrospinal fluid has been developed. Pirprofen is employed as internal standard. Samples are extracted with C18 solid-phase extraction columns and eluted with methanol. Oxidation potentials for detection were established by constructing voltammograms for each compound. In the concentration range found in human studies, the intra-day coefficients of variation were always less than 6%. The procedure allows the simultaneous determination of diclofenac and its four major metabolites with very low detection limits (less than 1 ng/ml), which were sufficient even for kinetic studies in cerebrospinal fluid.