Liquid-Liquid Extraction-Chromogenic System for Vanadium(V) Based on 4-(2-thiazolylazo)orcinol (TAO) and Aliquat 336

Abstract

The quaternary ammonium salt Aliquat 336 (A336; R₄N⁺Cl^-) and the azo dye 4-(2-thiazolylazo)orcinol (ТАО) were examined as constituents of a water-isobutanol extraction-chromogenic system for vanadium(V). Under the optimum conditions (c_TAO = 1.6´10^–3 mol dm^–3, c_A336 = 1.3´10^–2 mol dm^–3 and pH 5.0), vanadium(V) is extracted as a ternary complex which can be represented by the formula (R₄N⁺)[VO₂(TAO^2-)]. The key extraction-spectrophotometric characteristics were determined. The interfering effect of foreign ions was studied as well. The wavelength of maximum absorption (λ_max), molar absorptivity (ε_max), constant of extraction (K_ex) and fraction extracted (E) were found to be λ = 547 nm, ε = 3.1×10⁴ dm³ mol^–1 cm^–1, Log K_ex = 2.8 and E = 90.2%, respectively. Beer’s law was obeyed in the range of 0.084–2.0 mg cm^–3 and the limit of detection was 25 ng cm^–3 of vanadium(V).