INTRODUCTION

Fluoride present can be determined by either colorimetric method or Ion Selective Method. With colorimetric method, higher concentrations of fluoride cannot be determined. With ISE method, wide range of fluoride can be determined. Further, colour and turbidity will not interfere.

The fluoride electrode is an ion-selective sensor. The key element in the fluoride electrode is the laser-type doped lanthanum fluoride crystal across which a potential is established by fluoride solutions of different concentrations. The crystal contacts the sample solution at one face and an internal reference solution at the other. The reference electrode used is Ag/AgCl.

Fluoride forms complexes with several polyvalent cations, notably aluminium and iron. Use of TISAB provides uniform ionic strength background, adjusts pH and breaks up such complexes. CDTA (Cyclohexylene Diaxnine Tetra Acetic Acid), a component present in TISAB (Total Ionic Strength Adjusting Buffer), preferentially will complex with interfering cations and release free fluoride ions. By maintaining pH above 5.0, complex formation of hydrogen fluoride is avoided and interference of hydroxide ion is avoided by maintaining the pH below 5.5.

Fluoride is found in several minerals such as apatite, and mica. Fluoride is an essential element for the formation of healthy tooth enamel. For this purpose, fluoride-free drinking water in some of the city 1.5-2.5 mg/l fluoride will need to participate. However, fluoride is harmful is something more. Fluoride concentration of 5 mg/l can cause tooth decay more than the case. And use of fluoride in drinking water at 1.5 mg/l limit was put into the value. Fluoride in soil is in the form of both elements and minerals. Terms of volume, average 0.3 g/kg as the most common minerals in the fluoride Florist and Fluorspar. Naturally, the soils in the 30-300 ppm level fluoride generally reported to be harmless to plants and animals.

Relevant Indian Standard for Fluoride Test :

1. IS 3025 (Part 60) -2008 : Method of Sampling and Test (Physical and Chemical) for Water and Wastewater : Fluoride , First Revision.