An improved method for the spectrophotometric determination of fluoride by addition of sodium dodecyl sulphate to the fluoride/lanthanum (III)/Alizarin fluorine blue system

Abstract

The conventional spectrophotometric method for the determination of fluoride, based on the fluoride/lanthanum(III)/alizarin fluorine blue ternary complex, is improved by addition of sodium dodecyl sulphate. In 15% (v/v) acetone medium, the absorbance of the binary reagent complex is decreased and the reaction time is only 3 min under sonication. Beer's Law is obeyed at 574 nm for fluoride concentrations in the ranges 0.075–0.30 and 0.20–1.2 mg 1 −1; the apparent molar absorptivities are (1.6 ± 0.1) × 10 4 and (1.5 ± 0.1) × 10 4 mol −1 cm −1 fluoride levels, respectively. This method is applied to the determination of fluoride in bottled mineral waters.