A new, sensitive and versatile assay for quantitative determination of α-fluoro-β-alanine (AFBA) in human urine by using the reversed-phase ultrahigh performance-tandem mass spectrometry (rp-UHPLC-MS/MS) system.

A method for the quantitation of α-fluoro-β-alanine (AFBA), the main metabolite of capecitabine (Cape) and 5-fluoruracil (5-FU), is described. Among antineoplastic drugs (ADs), 5-FU and Cape (the new oral prodrug) are the most commonly applied drugs in cancer therapy. The main objective of this study was to develop a reliable method that would be easy to run on a reversed-phase UHPLC system coupled to tandem mass spectrometry. AFBA was derivatized with Sanger's reagent to ensure complete yield of a stable 2,4 dinitrophenil-α-fluoro-β-alanine derivative. This method was based on the use of a mixed-mode anion exchange solid phase extraction enabling urinary extracts to be clear of endogenous interferences affecting quantitative results. The assay was validated in human urine according to FDA criteria with the use of a labeled internal standard (β-alanine-d4) to minimize experimental error. Good accuracy and precision were demonstrated by determining spiked urine QC samples in four consecutive days. The recovery of AFBA was between 70.0 and 82.6%, with a matrix effect that was 12.8%-18.5%. The lower limit of quantitation (LOQ) was 0.5 ng/mL with a coefficient of variation of 5.3%. This assay was successfully applied to determine the levels of this metabolite in a large number of urine samples taken from personnel who were occupationally exposed to ADs.