Determination of Organically Bound Fluorine Using Sodium Biphenyl Reagent and a Fluoride-Specific Ion Electrode

A simple, accurate, and specific method for direct determination of carbon-bonded fluorine is described for various aromatic compounds of pharmaceutical interest, containing as little as 4% fluorine. Sodium biphenyl reagent was utilized for quantitative liberation of bound fluorine; a fluoride-specific ion electrode was used, in conjunction with a high ionic strength buffer solution, for direct measurement of the liberated fluoride. Incorporation of a subsequent „oxidation” step, using hydrogen peroxide, resulted in quantitative determination of fluorine for certain organo-fluoro compounds which were difficult to ionize completely using a modified oxygen flask combustion technique. It was possible to determine fluorine routinely for up to 20 samples in an 8-hr. period. Precision and accuracy studies are included.