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
2022
Mortada, Wael I. | El-Defrawy, Mohamed M. | Erfan, Eman | El-Asmy, Hala A.
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.
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