Studies of the Determination of Fluoride in Vegetation Samples

Abstract

The use of the Association of Official Analytical Chemists (AOAC) First Action method, which is based on acid leaching of the dried, ground sample, is examined for its suitability for the recovery of fluoride from leaf material derived predominantly from indigenous Australian trees. The method is compared with two independent but time-consuming procedures based on oxygen pyrolysis and pyrohydrolysis. These two reference methods give internally consistent results and provide a sound basis on which to critically examine the AOAC First Action method. It is concluded that the AOAC method, in general, gives reliable and rapid results, although two of the species studied showed a low fluoride recovery. The AOAC method uses a fluoride electrode finish which is slow for solutions of low concentration. A graphical procedure is examined for estimating the steady-state electrode potential; this procedure increases the speed of the analysis without affecting unduly the accuracy of the analysis.