Cloud point extraction coupled with back-extraction for speciation of inorganic vanadium in water and determination of total vanadium in food samples by ICP-OES

Abstract

A preconcentration procedure based on cloud point extraction and back-extraction (CPE-BE) was proposed for speciation of inorganic vanadium (V4+ and V5+) followed by determination by inductively coupled plasma-optical emission spectrometry (ICP-OES). Two consecutive steps are used in this technique. The traditional CPE technique was applied as a first step, V5+ reacts with bis(3,4-dihydroxybenzylidene)isophthalohydrazide (DHBIP) forming a hydrophobic complex at pH 7.0. The formed complex is then entrapped in a surfactant-rich phase of Triton X-114, while V4+ kept in the aqueous phase. Following this stage, a back-extraction step was performed to minimize the deteriorating effect of the organic matrix on the plasma performance. For this purpose, the surfactant-rich phase containing the analyte was incubated at 45 °C with 1.0 mL of 1.0 mol L−1 of HNO3 solution for 15 min. Finally, the analyte in the aqueous phase was determined by ICP-OES. The total vanadium was determined as V5+ after oxidation of V4+ by using hydrogen peroxide. The calibration graph is linear from 0.4–750.0 μg L-1 for V5+ at the optimum conditions (pH 7.0, 10-4 mol L-1 DHBIP, 0.1 % (v/v) Triton X-114 and 45 °C). The detection and quantification limits of V5+ were 0.12 μg L-1and 0.40 μg L-1, respectively, with an enrichment factor of 49.5, and the relative standard deviation was less than 2.5 % (n = 7, c = 10 μg L-1). The method has been used for speciation of inorganic V in water samples and determination of total V in cabbage, carrots, mint, and tomato samples with satisfactory results.