TOTAL FLUORIDE CONTENT OF HUMAN SERUM

The analysis of six human sera for its fluoride content by (a) fluoride ion-electrode determination in diffusates of unashed samples, (b) colorimetric determination in diffusates from unashed samples (Singer and Armstrong, 1965), (c) colorimetric and electrode methods applied to diffusates of ashed samples and (d) colorimetric assay of steam distilled ashed samples (Singer and Armstrong, 1959) are reported. Concordant results were obtained with ashed sera by all methods. Consistently higher results were obtained with ashed than with unashed samples when the fluoride ion-electrode was used. Evidence is presented that part of the fluoride evolved by diffusion from unashed samples is unavailable for measurement with the electrode. The determinations of total fluoride in serum requires ashing of the sample prior to diffusion or rigid adherence to 20-26 hr diffusion under prescribed conditions. Analyses of plasma of rats raised on different fluoride intakes are used to demonstrate the responsiveness of the direct diffusion method to variations of total serum fluoride contents. © 1969.