Gas-chromatographic method for the halothane metabolites, trifluoroacetic acid and bromide, in biological fluids

A simple and rapid method is presented for the quantitative determination of bromide and trifluoroacetic acid in urine, plasma or serum. The biological fluid is treated with dimethyl sulfate in an acidic medium, resulting in the formation of the methyl ester of trifluoroacetic acid and methyl bromide. The volatile derivatives are then isolated from the samples via a head-space technique, separated and resolved by gas chromatography, and detected by flame ionization. Detection of the two metabolites is linear within the sample concentrations studied. The method is reproducible and applicable to the determination of the two metabolites in biological fluids in the 0.1-10 mM concentration range. The method is comparable to previous techniques but is less time consuming, and both bromide and trifluoroacetic acid can be determined simultaneously. Preliminary pharmacological studies of urine and blood metabolite levels in rats and human patients anesthetized with halothane agree with existing results determined by other methods. In addition, the results indicate that bromide concentrations in human blood remain elevated for a much longer period of time than those in rat blood.