Limitations of the sodium fusion assay for fluorinated metabolites

A method involving sodium fusion and analysis by fluoride electrode, which has been used for the determination of total fluorinated metabolites of fluorine-containing drugs in physiologic fluids, is shown to be inapplicable to volatile fluorinated metabolites of volatile fluorinated anesthetic agents. The yields of inorganic fluoride from the volatile metabolites 2,2,2-trifluoroethanol and trifluoroacetaldehyde were less than 2% of expected values, whether these metabolites were present in water, buffer, urine, or hepatic microsomes, although reliable results were obtained for the relatively nonvolatile sodium trifluoroacetate. It is proposed that the assay does not provide a valid method for determining total fluorinated metabolites of volatile or nonvolatile fluorine-containing drugs, but may be of some use in determining a single nonvolatile fluorinated metabolite of a volatile fluorinated drug.