Development, validation and application of a novel liquid chromatography tandem mass spectrometry assay measuring uracil, 5,6-dihydrouracil, 5-fluorouracil, 5,6-dihydro-5-fluorouracil, α-fluoro-β-ureidopropionic acid and α-fluoro-β-alanine in human pl

The analytical response was linear (r2 ≥ 0.99) in the concentration (ng/mL) ranges: 50-10 000 for FβAL and FUH2, 50-5 000 for FUPA, 50-100 000 for 5-FU, 5-200 for U and 10-400 for UH2. Within- and between-run accuracy and precision were ≤ 10.2% and ≤ 9.8% respectively across the QC range and inclusive of LLOQ. The internal standard (IS) normalised matrix effects were within 93-112% with CV of ≤ 9.7% and normalised recoveries were within 91-107% with CV of ≤ 9.8%. This robust assay was successfully applied to samples from rectal and colorectal cancer patients (n = 10) on 5-FU. Deviations ≤ 2.0% from the mean values were observed when incurred samples were reanalysed.