Development of a UPLC-MS/MS Assay for the Quantitative Determination of Capecitabine, 5'-deoxy-5-fluorocytidine (5'-dFCR), 5'-deoxy-5-fluorouridine (5'-dFUR), 5'-fluorouracil (5-FU), and α-fluoro-β-alanine (FBAL)

Capecitabine is an anticancer agent and is the oral prodrug of 5-fluorouracil (5-FU). In this study, an ultra-high performance liquid chromatography coupled to turbo ion spray tandem mass spectrometry (UPLC-MS/MS) method was developed and validated to quantify capecitabine and its metabolites including 5’-deoxy-5-fluoro-cytidine (5’-dFCR), 5’-deoxy-5-fluorouridine (5’-dFUR), 5-FU, and fluoro-β-alanine (FBAL) in lithium heparinized human plasma. Analytes were extracted by protein precipitation, chromatographically separated by Acquity UPLC HSS T3 column with gradient elution, and analyzed with a tandem mass spectrometer equipped with an electrospray ionization source. Capecitabine and 5’-dFCR were quantified in positive ion mode and 5’-dFUR, 5-FU, and FBAL were quantified in negative ion mode. The total chromatographic run time was 9 min. Stable isotopically labeled internal standards were used for all analytes. The assay was validated over the range from 25.0 to 2,500 ng/mL for capecitabine, 10.0 to 1,000 ng/mL for 5’-dFCR, 5’-dFUR, and 5-FU and 50 to 5,000 ng/ mL for FBAL in human plasma. Validation results have shown the developed assay allows for reliable quantitative analysis of capecitabine, 5’-dFCR, 5’-dFUR, 5-FU, and FBAL in plasma samples.