Sulphonated alizarin fluorine blue (AFBS). Part III. Lanthanum(III) complexes of 1-hydroxyanthraquinone-2-sulphonate, alizarin-5-sulphonate and AFBS, the fluoride complex of AFBS-lanthanum and a suggested method for fluoride determination

Abstract

An attempt is made to understand the reaction for ternary complex formation between sulphonated alizarin fluorine blue (AFBS), lanthanum and the fluoride ion through study of complex-forming reactions between lanthanum and 1-hydroxyanthraquinone-2-sulphonate (HA2S), alizarin-5-sulphonate (A5S) and sulphonated alizarin fluorine blue, successively. Comparison of experimental molar-ratio and Job plots with those derived from theory reveals that HA2S forms 1:1 and 1:2 lanthanum-HA2S complexes of K₁₁^abs= 1.85 × 10⁷ l mol^–1 and K₁₂^abs= 1.29 × 10⁷ l mol^–1; A5S forms 1:1, 1:2 and 2:2 lanthanum-A5S complexes and AFBS forms 1:1, 2:1 and 2:2 lanthanum-AFBS complexes. Fluoride ions react to form FR and FR₂ complexes, where R represents a particular mixture of AFBS-lanthanum complexes. Conditions under which AFBS can best be used for the determination of fluoride are explored and such an analysis is compared statistically with one using the original alizarin fluorine blue; the latter performs well. The use of other lanthanoid ions is investigated.