Fluoride gives a very stable complex with scandium and, hence, by determining the unreacted scandium, the fluoride content can be calculated. Excess scandium is reacted with an ethanolic solution of N-benzoylphenylhydroxylamine (BPHA) at pH 6.0, and the scandium-BPHA complex is extracted into isoamyl alcohol. Scandium is determined spectrophotometrically after adding xylenol orange. Beer's law for fluoride is obeyed in the range of 0.05 #x2013;1.5 ppm; the molar absorptivity is 1.94#xD7;1041 mol#x2212;1at 565 nm. The procedure is applicable for the determination of fluoride in various types of samples.
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