Extraction-Chromogenic System for Nickel(II) Based on 5-methyl-4-(2-thiazolylazo)resorcinol and Aliquat 336

Abstract

A water-isobutanol extraction-chromogenic system for Ni^II, based on the azo dye 5-methyl-4-(2-thiazolylazo)resorcinol (MTAR; H₂L) and the ionic liquid Aliquat 336 (A336), was studied. Under the optimal conditions (c_MTAR = 2.0 × 10^–4 mol dm^–3, c_A336 = 5.6 × 10^–3 mol dm^–3, pH 8.5 and extraction time t = 1 min), Ni^II is extracted as a ternary complex which can be represented by the formula (A336⁺)₂[Ni(L^2-)₂]. In the absence of A336, or in a slightly acidic medium, a binary complex, [Ni(HL^-)₂], with an absorption maximum at l = 548 nm and a shoulder at 590 nm is formed. The following extraction-spectrophotometric characteristics were determined at the above-mentioned optimal conditions: l_max (545 nm), molar absorptivity (5.0 × 10⁴ dm³ mol^–1 cm^–1), Sandell’s sensitivity (1.2 × 10^–3 μg cm^–2), Beer’s law limits (0.05–3.1 mg cm^–3), constant of extraction (Log K = 6.1) and fraction extracted (99.2%). The effect of foreign ions was studied; the most serious interferences were caused by Co^II, Cu^II and Cr^III.