Indirect Colorimetric Estimation of Fluoride Ion in Water and Pharmaceutical Preparation Samples

An indirect method for the estimation of fluoride ion has been developed.The method is based on the bleaching action of fluoride ion on the color of Ti (IV)with 2-hydroxy-1-(2-hydroxy-4-sulfo-1-naphthylazo)-3-naphthanic acid (HHSNNA) complex with proportional decrease of absorbance. Therefore,the decrease in color intensity is proportionalto the concentration of fluoride ion. Molar absorptivityis 0.1166104 l. mol-1.cm-1 atwavelength 685 nm. Beer's lawis obeyed over the concentration range of 0.2-4 g/ml.The proposed method is applied successfullyto determine fluoride ion in different real water samples andpharmaceutical preparations (Tablets). The proposed method is compared favorably with Eriochrome cyanine R Zirconium method .