A low-cost device for the estimation of fluoride in drinking water

Fluorosis is endemic in many regions of the world due to high (>1.5 mg I-1) levels of fluoride in groundwater. This problem is aggravated by the lack of a simple and inexpensive test for fluoride in drinking water. We discuss the design and testing of a low-cost LED-based colorimeter for estimating the fluoride concentration in water. The device was calibrated with the use of the cerium-alizarin complexone (Ce-AC) and the sodium 2-(parasulfophenylazo)-1,8-dihydroxy-3,6-naphthalene disulfonate (SPADNS) methods, which show color changes in the visible region on addition of water containing fluoride. Raw water samples collected from different parts of India were analyzed for fluoride. The fluoride concentration, as estimated by using a fluoride electrode, was in the range 0.7-1.20 mg I-1. The results obtained by the colorimeter showed good agreement with the electrode method for most of the samples. The cost of chemicals per test was $0.14 for the Ce-AC method and $0.018 for the SPADNS method. The cost of the colorimeter was about $14