Innovative dispersive liquid-liquid semi-microextraction approach for the speciation of V(IV) and V(V)

The complexation of V(IV, V) species with 2,4-substituted derivatives of 6,7-dihydroxybenzopyrylium bromide has been studied. The stoichiometry of the interaction products in the studied systems M : L = 1 : 3 was established by classical spectrophotometric methods. It was shown that the introduction of phenyl substituents at positions 2 and 4 of the benzopyrylium fragment leads to a shift of complexation to a more acidic region, an increase in the stability of the reaction products, and an increase in their molar absorptivity. It is substantiated that the reagent 6,7-dihydroxy-4-methyl-2-phenylbenzopyrylium bromide seems to be the most convenient for the development of semi-microextraction-UV-Vis spectrometric method for the V(IV, V) speciation. The apparent molar absorptivity of the complexes in the organic phase is 9.5 × 10⁴ L mol^-1 cm^-1 for V(IV) and 1.0 × 10⁵ L mol^-1 cm^-1 for V(V), respectively. The enrichment factors for V(IV) and V(V) are 9.5 and 10, respectively. The preconcentration factor is 9.3. An innovative approach for dispersive liquid-liquid semi-microextraction preconcentration and spectrophotometric determination of vanadium has been developed (recoveries are 99.3-101.5%). The use DMF as auxiliary solvent allows to the separate extraction and determination of V(IV, V) form in their mixture. The greenness of the method was evaluated via AGREE and BAGI software.