STUDY OF COMPLEX EQUILIBRIA IN NIOBIUM(V) AND VANADIUM(V) SYSTEMS WITH 2-(5-BROMO-2-PYRIDYLAZO)-5-DIETHYLAMINOPHENOL, TARTRATE AND HYDROGEN-PEROXIDE USING RP-HPLC

Complex equilibria in multiligand niobium(V) systems with 2-(5-bromo-2 -pyridylazo)-5-diethylaminophenol (5-Br-PADAP), tartrate and hydrogen peroxide and vanadium(V) with 5-Br-PADAP and tartrate were evaluated b y reversed-phase high-performance liquid chromatography (RP-HPLC) usin g C-18 column and VIS detection at 590 nm. In all examined systems pre -column derivatization was performed in water-methanol [20 %(V/V)] med ium at pH 3.5-3.8. The formed complexes were eluted using tetrahydrofu ran-methanol-water mobile phase containing acetate buffer (pH 3.7). In Nb(V)-H2O2-tartrat-(5-B r-PADAP) system formation of multiligand niob ium complex, non-reactive towards 5-Br-PADAP, was postulated. For V(V) system distribution of metal ion between V(V)-(5-Br-PADAP) binary and V(V)-tartrate(5-Br-PADAP) ternary complexes was evaluated. On this ba se it was proved, that coloured ternary vanadium complex is only an in termediate stage in the formation of stable V(V)-tartrate binary compl ex.