SIMULTANEOUS DETERMINATION OF 5'-DEOXY-5-FLUOROURIDINE, 5-FLUOROURACIL AND 5,6-DIHYDRO-5-FLUOROURACIL IN PLASMA BY GAS-CHROMATOGRAPHY MASS-SPECTROMETRY

A gas chromatography-mass spectrometry (GC-MS) method for the simultan eous determination of 5'-deoxy-5-fluorouridine (doxifluridine, 5'-dFUR ), 5-fluorouracil (5-FU) and its main catabolite 5,6-dihydro-5-fluorou racil (5-FUH2) in human plasma has been developed. Sample preparation consisted of protein precipitation with ammonium sulphate followed by analyte extraction with ethyl acetate/isopropanol (90/10, v/v) mixture . Extracts were then analysed by GC-MS in positive electron impact mod e after derivatization with N,O-bis(trimethylsilyl)trifluoroacetamide (1/1, v/v). The trimethylsilyl (TMS) derivative of 5'-dFUR was proved to be stable so that no interference in 5-FU determination was observe d. Mass spectra of TMS derivatives of 5'-dFUR, 5-FU and 5-FUH2 are dis cussed. Analyte response was linear over two decades of concentration and detection limits were typically 20 ng/ml of plasma.