Development of a sensitive and selective LC-MS/MS method for the determination of alpha-fluoro-beta-alanine, 5-fluorouracil and capecitabine in human plasma.

A sensitive and selective quantitative method to determine alpha-fluoro-beta-alanine (FBAL), 5-fluorouracil (5-FU), and capecitabine (Cape) from a single human plasma aliquot (50 microL) has been developed and validated. First, 5-FU and Cape were extracted by liquid-liquid extraction (LLE) using a mixture of acetonitrile and ethyl acetate. This was followed by derivatization with dansyl chloride. The dansyl-derivatives from 5-FU and Cape were further purified using LLE with methyl tertiary-butyl ether (MTBE) and analyzed using a reversed-phase analytical column "Primesep D" (2.1 mm x 50 mm; 5 microm) with embedded basic ion-pairing groups. The remaining aqueous phase containing FBAL was treated with dansyl chloride and the dansyl-FBAL was purified by solid phase extraction. Ultra high pressure liquid chromatography (UPLC) technology on a BEH C18 stationary phase column with 1.7 microm particle size was used for analysis of dansyl-FBAL. The method was validated over the concentration ranges of 10-10,000, 5-5000, and 1-1000 ng/mL for FBAL, 5-FU, and Cape, respectively. The results from assay validation show that the method is rugged, precise, accurate, and well suited to support pharmacokinetic studies where approximately 300 samples can be extracted and analyzed in 1 day.