RP-HPLC STUDY OF REDOX EQUILIBRIA IN VANADIUM-PAR BINARY AND TERNARY-SYSTEMS - DIRECT DETERMINATION OF VANADIUM IN STEEL

The reversed-phase high-performance liquid chromatographic (RP-HPLC) b ehaviour of the binary chelates of V(V) and V(IV) with 4-(2-pyridylazo ) resorcinol (PAR) and ternary chelates of vanadium with PAR and auxil iary ligands: hydrogen peroxide, hydroxylamine, tartrate and citrate w ere studied using a C-18 column. The complex double-peak chromatograms of V(IV)/V(V)-PAR systems were studied and the origin of each peak wa s proved. Vanadium in ternary systems with PAR and hydrogen peroxide w as found exclusively in V(V)-H2O2-PAR complex (single peak on the chro matogram) despite its initial oxidation state. The double role of hydr oxylamine (complex agent and reductor) in vanadium systems with PAR wa s confirmed: in the V(V) system three species were identified (V(V)-PA R, VM-NH2OH-PAR and V(IV)-PAR), but in the V(IV) system only two: V(IV )-PAR and V(V)-NH2OH-PAR. Citrate and tartrate giving single peak were found as auxiliary ligands in ternary V(V) systems of analytical impo rtance. Due to its masking potential towards iron (III) ions, citrate was chosen as the most suitable third component of a ternary vanadium system with PAR, to form the basis of an RP-HPLC method for direct det ermination of V in steel.