Spectrophotometric determination of boron in natural waters by solvent extraction with chromotropic acid and removal of the excess of reagent

Abstract

A method of removing the excess of reagent extracted into an organic phase in the solvent extraction of metal complex anions with quaternary ammonium salts was applied to the solvent extraction of the boron complex anion formed with chromotropic acid (1,8-dihydroxynaphthalene-3,6-disulphonic acid) by using zephiramine (tetradecyldimethylbenzylammonium chloride). EDTA, chromotropic acid, zephiramine and buffer (pH 3.5) are added to the sample solution, which is then shaken with 1,2-dichloroethane. The organic phase is washed twice with a back-washing solution (0.6 M in sodium chloride, pH 9.2) and the absorbance of the organic phase measured in a quartz cell. The boron complex is extracted quantitatively into the 1,2-dichloroethane and its apparent molar absorptivity in 1,2-dichloroethane is 1.4 × 10⁴ l mol^–1 cm^–1 at 351 nm. Micro and trace amounts of boron in natural waters are determined spectrophotometrically.