HPLC ANALYSIS OF V, CO, FE, AND NI BY 4-(2-PYRIDYLAZO)-RESORCINOL, PAR, AND H2O2 AND STUDIES ON COMPLEX PROPERTIES INFLUENCING RETENTION

Metal ions of V, Co, Fe, Ga and Ni are separated by adding PAR and H2O2 to an aqueous sample at pH 6.5 and the complexes are determined by HPLC with LiChrosorb RP-18 and methanol-water as mobile phase. The chromatograms using pre-column in combination with on-column derivatisation of V, Co, Fe and Ni have shown them to be ternary V-PAR-peroxo and binary M-PAR (M = Co, Fe, Ni) complexes, respectively. The calibration curves obtained for 20-mu-l samples were linear for 0.02-0.4 mg/l V, 0.02-1.0 mg/l Co, 0.02-0.9 mg/l Fe and 0.06-0.9 mg/l Ni. The relative standard deviations were between 2.5 and 10%. In addition, the stability constants of various M-PAR complexes have been calculated from multiwavelength spectrophotometric data. The calculations indicated that at pH 6.5 mainly the complexes V(PAR), V(PARH), Co(PAR)2, Fe(PAR)2, Fe(PARH), Fe(PARH)2, Ni(PAR)2 and Ni(PARH)2 could be formed. The experimental and calculated results have shown that the retention times (t(R)) were qualitatively inversely and directly proportional to the mixed molar extinction coefficient epsilon(mix) of the complexes and the change in free energy of formation of the hydrous metal ions, respectively.