RAPID METHOD FOR DETERMINING FLUORIDE IN VEGETATION USING AN ION-SELECTIVE ELECTRODE

Fluoride was extracted from dried vegetation by stirring with 0. 1 N perchloric acid for 20 min at 20 °C. The fluoride content was determined in this extract (pH 1) using the method of standard additions, thus eliminating the need to de-complex fluoride prior to analysis. The presence of up to 2.0% of silicon, 0.06% of iron, 0.1% of aluminium, 0.7% of magnesium and 1.2% of calcium did not result in any interferences and recoveries of 98-102% were obtained. The fluoride contents of standard samples determined by this method were highly correlated (r = 0.999) with those obtained by reference methods over the range 4-2 000 μg g-1 of fluoride in the dry matter.