HPLC analysis of V, Co, Fe, and Ni by 4-(2-pyridylazo)-resorcinol, PAR, and H₂O₂ and studies on complex properties influencing retention

Summary

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 μl 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 ε_mix of the complexes and the change in free energy of formation of the hydrous metal ions, respectively.