Abstract
A calcium hydrogen phosphate dihydrate (DCPD) reacts with fluoride ion in a solution to form fluorapatite (FAp). This reaction is very selective and efficient enough. The aim of this paper was to develop a simplified method of determination of trace amounts of fluoride in air using transform reaction of DCPD. In this paper, a suitable pH range to fix fluoride in the air to form of fluoride ion was assessed based on chemical equilibrium. It is found that a suitable pH for fixation of fluoride in the air is up to 5.5. The pH of the solution is adjusted about 7.5 because of buffer action derived from DCPD and carbon dioxide in the air. From these results, we have developed a simplified determination of trace amounts of fluoride in the air based on the characteristic of the reaction. Fluoride in the air was collected through water containing DCPD powder. The fluoride in separated as FAp is dissolved in 10 ml solution of pH 7.0 containing NaCl, CyDTA and HEPES. The concentration of fluoride ion in the solution is readily measured by using fluoride ion selective electrode.
