Evaluation of analytical methods for fluorine in biological and related materials

During the past two decades, some major pitfalls in fluorine analysis have been recognized and overcome. Therefore, it is important that facts be separated from fallacies in published literature on levels and forms of fluorine (ionic, bound, covalent, etc.) in biological materials, in order that correct perceptions of physiological, biochemical, and toxicological aspects of inorganic as well as organic fluorine compounds can be formed. Trace amounts of inorganic fluoride in biological samples can now be accurately determined with the fluoride electrode either directly or following diffusion, adsorption, or reverse extraction of fluoride (when necessary). The aluminum monofluoride molecular absorption technique provides an excellent rapid method for determination of trace amounts of inorganic fluoride (in the absence of organic fluorine). Fluorine in most organic fluorine compounds is not available for distillation, diffusion, or reverse-extraction. The sample needs to be ashed (open ashing) or combusted (oxygen flask, oxygen bomb, pyrohydrolysis) for covalently bound fluorine to be converted to fluoride ions. This can now be readily accomplished at room temperature by the reductive cleavage of the C-F bond with the sodium biphenyl reagent. Some recommendations for future research have been made.