Spectrophotometric determination of fluoride using ternary complex of zirconium with Eriochrome Cyanine R and cetylpyridinium ions

Abstract

The possibility of indirect spectrophotometric determination of fluoride based on the ternary complex of zirconium (IV) with Eriochrome Cyanine R (ECR) and cationic surfactant (cetylpyridinium ion, CP; cetyltrimethylammonium ion, CTA; tetradecyldimethylbenzylammonium ion, zephiramine) was examined. A new sensitive method for fluoride determination, based on Zr-ECR-CP system, was developed. The molar absorptivity is 5.9 × 10 4 liters mol −1 cm −1 at λ = 610 nm. The optimum conditions for obtaining the best analytical effect were specified as follows: pH 1.10 ± 0.10 (HCl), the molar ratio of zirconium (IV) to Eriochrome Cyanine R in Zr-ECR reagent = 1:4; 15-fold molar excess of CP with respect to zirconium, the sequence of adding the reagents-solution containing fluoride, Zr-ECR reagent, CP. Absorbance is measured after 5 min. The proposed method proves to be precise and accurate, as demonstrated by the example of the analysis of tap water with and without the addition of the known microgram amounts of fluoride.