FIGURE 3. Analysis of ¹⁸F-labeled metabolites in arterial plasma. (A and B) Radiochromatograms obtained by isocratic-elution HPLC of acid-soluble extract from samples taken 90 min after intravenous injection of [¹⁸F]FU into a rat pretreated with eniluracil (A) and 60 min after intravenous injection of [¹⁸F]FU into a rat not pretreated with eniluracil (B). (C) UV absorbance chromatogram (wavelengths 254 nm) of an authentic sample of FU, which was obtained just before the radiochromatogram of (A). (D) UV absorbance chromatogram (wavelengths 214 nm) recorded simultaneously with radiochromatogram of (B). An aliquot of solution containing authentic, nonradiolabeled samples of -fluoro-ß-alanine (FBAL), dihydrofluorouracil (FUH₂), FU, fluorouridine (FUrd), and fluorodeoxyuridine (FdUrd) was added to the injectate in the run depicted in (B and D). Radiochromatogram for ¹⁸F-labeled fluoride ion ([¹⁸F]F^–) (dashed lines in D) was determined separately. Percentages of recovered radiolabel associated with various peaks are shown in (A and B).