High concentration of Fluoride in drinking water causes dental Fluorosis. Under acidic conditions fluorides (HF) react with zirconium SPADNS solution and the lake (colour of SPADNS reagent) gets bleached due to formation of ZrF6. Since bleaching is a function of fluoride ions, it is directly proportional to the concentration of fluoride. It obeys Beers law in a reverse manner

Material and apparatus

·         Spectrophotometer

·         Samples cells

·         SPADNS solution

·         Pipette

·         Beaker

·         Distilled water

Procedures:

·         Turn on spectrophotometer

·         Select the test

·         Prepared Sample: Pipet 10.0 mL of sample into a dry sample cell.

·         Blank Preparation: Pipet 10.0 mL of deionized water into a second dry sample cell.

·         Carefully pipet 2.0 mL of SPADNS Reagent into each cell. Swirl to mix.

·         Start the instrument timer. A one-minute reaction period will begin.

·         When the timer expires, insert the blank into the cell holder.

·         ZERO the instrument. The display will show:0.00 mg/L F–

·         Insert the prepared sample into the cell holder. READ the result in mg/L F–. 

References

1. Sadhana C.; Ananda Dev G.; Handbook of Water, Air and Soil Analysis; a Lab Manual; International-E-Publication;2014

2.Frank R.Spellman; Handbook of water and wastewater treatment plant operations; Lewis publishers;2003

3.Leena Deshpande;Water Quality Analysis Laboratory methods; New Delhi; India.