FLUORIDE

References:
APHA Standard Methods, 20th ed., p. 4-82, method 4500 F^-  (1998).
USEPA Methods for Chemical Analysis of Water and Wastes, method 340.1 (1974,1978).
Thomas and Chamberlain, 1974, Colorimetric Chemical Analytical Methods, 8th ed., pp 186-193.

Fluoride can occur naturally in water, and may also be added in controlled amounts. Accurate determination of fluoride concentrations has become increasingly important as the practice of fluoridation of drinking water supplies as a public health measure has increased.

Monitoring and maintaining optimum fluoride levels is essential to maintain effectiveness and safety of the fluoridation process. The Maximum Contaminant Level for fluoride in drinking water is 4.0 mg/L. Fluoride compounds are also involved in the production of aluminum, steel, uranium, cement, enamel, and plastics.

The Fluoride Vacu-vials^® test method is based on the reaction between fluoride and a red zirconium-dye lake that has been formed with SPADNS. The loss of color resulting from the reaction of the fluoride with the dye lake is a function of the fluoride concentration. Results are expressed in ppm (mg/Liter) F^-.

This method is approved by the EPA for NPDES and NPDWR reporting purposes when the samples have been distilled from an acid solution. Seawater and wastewater samples must be pre-distilled. Distillation removes most contaminating interferences except chlorine. Sodium Arsenite has been added to remove up to 5 mg/L chlorine.