Simultaneous determination of doxifluridine and 5-fluorouracil in monkey serum by high performance liquid chromatography with tandem mass spectrometry.

A reverse-phase high performance liquid chromatography method with electrospray ionization and detection by mass spectrometry is described for the simultaneous determination of doxifluridine and its active metabolite 5-fluorouracil in monkey serum. A liquid/liquid extraction with ethyl acetate (90%) and isopropyl alcohol (10%) was used to extract simultaneously doxifluridine and 5-FU which have considerable difference in the polarity. Optimum chromatographic separation was achieved on a Agilent Zorbax C(18) (100 mm x 2.1mm, 3.5 microm) column with a mobile phase of methanol-water (20:80, v/v). The flow rate was 0.2 mL/min with total cycle time of 5 min. The lower limit of quantification (LLOQ) was validated at 10.0 ng/mL of serum for both doxifluridine and 5-FU. Accuracy and precision of quality control (QC) samples for both compounds met FDA Guidance criteria of +/-15% with average QC accuracy of 95.5-105.0% and coefficients of variation of 1.1-9.5% in the 10-2000 ng/mL concentration range. This method demonstrated adequate sensitivity, specificity, accuracy, precision, stability to support the analysis of monkey serum samples.