Spectrophotometric determination of vanadium(V) with 2-carbethoxy-5-hydroxy-1-(4-tolyl)-4-pyridone

Vanadium(V) in aqueous HCl, HNO3 or H2SO4 solutions is extracted with 2-carbethoxy-5-hydroxy-1-(4-tolyl)-4-pyridone (HA) dissolved in CHCl3 and determined spectrophotometrically, Depending on the composition of the aqueous phase, two complexes are formed. At pH 1 (HCl, HNO3, H2SO4) VO2A(HA)2 is formed with maximal absorption at 478 nm. However, from 4-5 M HCl, VO2Cl(HA)3 is extracted, and has maximal absorption at 615 nm. The same complex is extracted from 2-3 M HNO3 or 3-4 M H2SO4 if enough chloride is added. Solutions of both complexes follow Beer's law and the molar extinction coefficients are 4.15x103 1.mole-1cm-1 at 478 nm and 5.10x103 at 615 nm. The determination of vanadium at both wavelengths is very simple, fast and selective. The composition of the complexes was established by the usual methods as well as by characterization of the isolated crystalline compounds by elemental analysis and infrared spectroscopy. (author)