Analysis of fluorouracil in human plasma by combined gas-liquid chromatography mass spectrometry.

Fluorouracil in human plasma of a concentration as low as 2 ng ml-1 can be assayed with the use of gas-liquid chromatography and a multiple ion detector. Fluorouracil is isolated from plasma by anion exchange extraction. The extract is butylated and the derivative obtained extracted into a mixture of cyclohexane + dichloromethane (95:5). An aliquot is submitted to combined gas-liquid chromatography mass spectrometry. The use of chlorouracil or oxygen-18 labelled fluorouracil as internal standard is discussed. Linearity is proven from 100 microgram to 5 ng of fluorouracil per ml plasma. The coefficients of variation are 7.2 and 8.4% for within-run and between-run precision, respectively, at the 50 ng ml-1 level. The biological applicability of our procedure is demonstrated by analysing plasma samples obtained at different time intervals from three patients given 1 g of fluorouracil once intravenously and once orally.

Flame-ionization GLC assay for fluorouracil in plasma of cancer patients.

A rapid and specific flame-ionization GLC method was developed for the determination of plasma fluorouracil. The chloro analog is used as the internal standard. The method involves the isolation of both the drug and the internal standard from plasma on a strong anion-exchange column at pH 10. Elution is performed with acetic acid in methanol. The evaporated eluate is dissolved in tetrahexylammonium hydroxide. An aliquot of the resulting solution is introduced directly into the gas chromatograph, where conversion to the bishexyl derivatives and subsequent separation take place. The extraction recovery from blank plasma, to which fluorouracil was added, was 96.8 +/- 2.4% (SD). Linearity was proven in the range from 0 to 25 micrograms/ml, whereas the detection limit of the method was estimated at about 2 micrograms/ml of plasma. The within-run precision was determined at three different fluorouracil levels. To demonstrate method applicability, plasma samples obtained from cancer patients to whom 1 g of fluorouracil had been administered intravenously were analyzed.

Gas-liquid chromatography of some alkyl derivatives of 5-fluorouracil.

Various procedures for converting 5-fluorouracil into its methyl, butyl and hexyl derivatives are described. Structures were established as the N,N'-dialkyl derivatives using mass spectrometry or combined gas-liquid chromatography-mass spectrometry. The reaction conditions, i.e., the amount of derivatization reagents and reaction time, were optimized. Gas-liquid chromatographic characteristics of the derivatives were investigated on different stationary liquid phases, and 2% or 3% SP-2250, 5% XE-60 and 5% OV-1 were found to be superior. With 5-chlorouracil as the internal standard a linear response for the various derivatives was observed in the microgram range. The applicability of the different dialkyl derivatives in the measurement of 5-fluorouracil in biological materials is discussed.

Application of ion-pair methods of extraction of fluorouracil from aqueous fluids.

The polar molecule, fluorouracil, is a monoanion at pH 10 and may be quantitatively extracted from aqueous solutions with quaternary alkylammonium ions into an organic solvent such as dichloromethane as the ion-pair. Extraction constants of fluorouracil with the tetrapentylammonium ion in dichloromethane or dichloromethane-1-butanol (9:1) and with the tetrahexylammonium ion in dichloromethane were determined. Slope analysis demonstrated that association of the ion components in the aqueous phase occurred as the side reaction. A column ion-pair extraction technique, using tetrapentylammonium as the counterion and dichloromethane as the eluting phase, was developed and allowed quantitative transfer of fluorouracil to the organ solvent. The applicability of this method was shown by determining plasma levels of fluorouracil in cancer patients to whom 1 g of active substance was administered intravenously.