ABSTRACT
Fluoride is a halogen ion that occurs in potable water and wastewater. It may also occur in soil, sediments, hazardous waste, aerosols, and gas. While a low concentration of fluoride (below 1 ppm at a controlled level in drinking water) is beneficial for reducing dental caries, a higher content is harmful. Fluoride in water may be determined by one of the following methods: colorimetric sodium 2-(parasulfophenylazo)-1,8-dihydroxy-3,6-naphthalene disulfonate (SPADNS) method, colorimetric automated complexone method, ion-selective electrode method and ion chromatography. Colorimetric SPADNS method and colorimetric automated complexone method are colorimetric techniques based on the reaction between fluoride and a dye. Zirconyl-acid–SPADN reagent is made by combining equal volumes of SPADNS with zirconyl-acid reagent. The former is prepared by dissolving 1 g of SPADNS in 500 mL distilled water. The latter is made by dissolving 0.14 g zirconyl chloride octahydrate in 50 mL of distilled water followed by addition of 350 mL conc. HCl and dilution to 500 mL.
