Sulphonated alizarin fluorine blue: an improved reagent for the positive absorptiometric determination of the fluoride ion

Abstract

Alizarin fluorine blue, [3-NN-di(carboxymethyl)aminomethyl]-1,2-dihydroxyanthraquinone, has been modified by the introduction of a sulphonate group in to the 5-position. The complex formed by lanthanum(III) with this new compound demonstrates a reaction towards fluoride similar to that shown by the complexes formed by lanthanum and cerium(III) with the original alizarin fluorine blue but with the added advantage of increased solubility. This allows a metal to reagent complex ratio of 2:1 to be used, which gives considerable increase in sensitivity towards fluoride.