Diffusion Method for Determination of Urinary Fluoride

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Abstract
A simple and inexpensive method is presented for determination of fluoride in urine. No preliminary treatment is required and operator time is greatly reduced since samples can be conveniently processed in large groups. A 1 ml portion of the urine specimen is placed in a miniature, disposable, plastic Petri dish containing a chloride fixative. The sample is acidified and the dish closed with a cover coated on the inner surface with sodium hydroxide. After diffusion for 20 hours at 50°C, fluoride held in the caustic film is determined spectrophotometrically either by use of an improved thorium-Alizarin Red S-buffer reagent or zirconium-Eriochrome Cyanine R reagent. Blanks are of submicrogram magnitude and, within the concentration range of 0-25 μg F- per ml, precision and accuracy are at least comparable to those of the distillation procedure.