Solid-phase extraction of fluoropyrimidine derivatives on a copper-modified strong cation exchanger: determination of doxifluridine, 5-fluorouracil and its main metabolites in serum by high-performance liquid chromatography with ultraviolet detection.

A copper-modified strong cation exchange stationary phase was used for the solid phase extraction of the antineoplastic drug doxifluridine (5'-deoxy-5-fluorouridine) and some of its main metabolites from human serum. Sorption of fluoropyrimidine derivatives due to complex formation with copper(II) was maximal at pH values around neutrality. Analytes were eluted by ligand exchange with ammonia. The average recoveries ranged from 70% to 108%. Reversed-phase chromatography with ultraviolet detection was used for the separation and quantitation of the analytes. The overall procedure has been applied to serum samples from patients receiving doxifluridine chemotherapy, and a pharmacokinetic profile has been derived.