Complex formation in a liquid-liquid extraction system containing vanadium(IV/V), 2,3-dihydroxynaphtahlene and thiazolyl blue

Abstract

Liquid-liquid extraction systems for VIV/V containing 2,3-dihydroxynaphtahlene (DN) and 3-(4,5-dimethylthi-azol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (thiazolyl blue, MTT) were studied. The optimum conditions for VIV and VV extraction were found. VIV is extracted in chloroform as a 1:2:2 complex (V:DN:MTT) with λmax = 570 nm and ε570 = 2.9 × 104 dm3 mol-1 cm-1. However, this wavelength was found unsuitable for precise spectrophotometric measurements due to time dependent absorbance changes. VV forms predominantly a 1:1:1 complex with λmax = 335 nm. The calibration graph for this oxidation state is linear in the range of 0.06-1.5 µg cm-3. The molar absorptivity, Sandell's sensitivity and limit of detection were calculated to be 1.6 × 104 dm3 mol-1 cm-1, 3.2 ng cm-2 and 0.02 µg cm-3, respectively. The ground-state equilibrium geometries of the anionic parts of the extracted ion-associates, [VIVO(DN2−)2]2− and [VVO2(DN2−)]−, were optimized at the BLYP/6-31++G* level of theory.