RESUMO
According to the importance of fluoride in water based on "DMFT" and 2 other reports which indicates that Spectrophotometeric method for measurement the fluoride water can not show the real amount of flouride, Potentiometer seems to be better than Spectrophotometer. To compare these two methods for measuring the amount of flouride, this research carried out in organic chemistry laboratory of Tehran University between 2006 and 2007. In this descriptive study, after obtaining the distilled water, they were prepared in 7 groups with 0, 0.35, 0.67, 0.7, 1, 1.2, 1.5 ppm of fluoride in 14 polyethylene containers and 2 samples were prepared from each type. In following, half of them were measuerd by standard spectrophotometer method [with the use of visible instrument in the same wave length, amount of light coefficient with standard solutions]. Using standard solutions of 10[-1] M up to 10[-5] M fluoride in the other half of samples, the calibration curve according to the findings was drawn. By studying the potentiometer amounts of samples and compare them with calibration curve, sample density were found. At the end, findings were changed to ppm. Therefore, the amount of fluoride in water were determined and the difference to the real fluoride in samples in each method were indicated. This difference in each method was calculated by paired-t test, whereas Mann-Whitney U test evaluated two groups with each other. The research studied 14 water samples with real fluoride of 0.77 +/- 0/58. In spectrophotometer method the fluoride amount was 0.99 +/- 0/58 with the difference of 0/82 +/- 0.23 from real amount [P<0.5]. In potentiometer this amount was 0.77 +/- 0/52 with the difference of 0.02 +/- 0.01. [P<0.4]. Amount of fluoride in spectrophotometer is 19.5% higher than potentiometer. Potentiometer method is better than spectrophotometer for indicating the fluoride in water and this method is, therefore, recommended