Spectrophotometric analysis for fluorouracil in biological fluids.

Fluorouracil (5-fluorouracil; 5-FU) is a monoanion at pH = 10 and forms an ion-pair complex with a quaternary alkylammonium ion. De Leenheer and co-workers [2] reported that the ion-pair complexes might be quantitatively extracted from aqueous solutions into organic solvents, and they spectrophotometrically determined the concentration of 5-FU. But as their method used column chromatography, it was cumbersome and time-consuming. Here we present a more rapid chemical assay of 5-FU by modifying the principle of their method. The applicability of this method was shown by determining the plasma and tissue levels of 5-FU in mice.