Determination of dissociation rate constant of oxine-copper complex using high-performance liquid chromatography

The solvolytic dissociation kinetics of the oxine-copper complex This (8-quinolinolato) copper (II)} was Studied with a reversed-phase high-performance liquid chromatography and spectrophotometry. The analysis of the chromatographic peak height of the complex, which decreased with a decrement of the flow rate of the eluent (water-acetonitrile (70 : 30 wt%)}, gave an apparent rate constant k(d) of 1.4 0.5 X 10(-4) s(-1) for the dissociation reaction. With the spectrophotometric method, the apparent rate constant k(ex) of the ligand exchange with EDTA was determined to be 0.75 +/- 0.11 s(-1). The observed small value of k(d), compared to the value of k(ex), call be attributed to the difference of mechanisms between the ligand-exchange reaction and the solvolytic dissociation. The value of k(ex) is controlled by the concentration of EDTA, indicating that EDTA was involved with the rate-determining step of the ligand-exchange reaction. On the other hand, the solvolytic dissociation of the oxine-copper complex is induced by a lack of 8-quinolinol around complex.