A comparison of results of fluoride determinations by different laboratories

With water fluoridation imminent in South Africa, the accurate determination of the fluoride content of water is important. The aim of this study was to compare the fluoride content of water reported by 9 laboratories and the laboratory at the South African Bureau of Standards (SABS). The SABS and 9 South African laboratories were asked to determine the fluoride content of five water samples. The fluoride content of the samples was in a range that could be expected in South African waters. The laboratories were requested to disclose their methods for fluoride determination. The results reported by the laboratories were compared to the results reported by the SABS laboratory. Fluoride concentrations of 0.13, 0.22 and 0.58 mg/litre were reproduced to within 0.05 mg/litre by two, six and three laboratories respectively. At the 1.1 and 1.5 mg/litre concentration no laboratory could achieve this accuracy. Four different methods for the determination of fluoride were used. At present laboratories determining fluoride concentrations are not accurate enough to ensure that the process of water fluoridation will be safe. Laboratories will have to check their procedures to ensure better results before water fluoridation can commence.