リン酸水素カルシウム二水和物（ＤＣＰＤ）の転化反応を用いた地下水中微量フッ化物の簡易定量法

Abstract

Ion-selective electrodes (ISE) are widely utilized for the determination of fluoride in water. For the determination of trace amounts of fluoride in groundwater, a pre-concentration process is required because of lack of sensitivity of ISE to fluoride. Calcium hydrogenphosphate dihydrate (DCPD) efficiently reacts with fluoride ion in a solution to form fluorapatite (FAp). The aim of this study was to develop a simplified method of determination of trace amounts of fluoride in groundwater using DCPD. In this paper, a suitable pH range for measuring fluoride using ISE was assessed on the basis of chemical equilibrium. It was found that the suitable pH for fluoride determination by ISE is 5.5-7.0, and FAp can be dissolved in this pH range by the complex-forming reaction of CyDTA. From the obtained results, a simple method for determining trace amounts of fluoride in groundwater has been established. Fluoride in a 100 ml water sample is quantitatively fixed as FAp using 0.10 g of DCPD at 60°C for 1hr. The fluoride that separated as FAp is dissolved in a 10 ml solution containing NaCl, CyDTA and HEPES. The amount of fluoride ion in the solution is easiliy measured by using ISE.