CENTRIFUGAL PARTITION CHROMATOGRAPHY OF PALLADIUM(II) AND THE INFLUENCE OF CHEMICAL KINETIC FACTORS ON SEPARATION EFFICIENCY

Separation efficiencies in the centrifugal partition chromatographic (CPC) method for the distributing species, a palladium ion complex and an organic solute (3-picoline) for the heptane: water phase pair have been compared. The column efficiency for the Pd(II)-TOPO (trioctylphosphine oxide) system (N = 500 +/- 40) has been found to be significantly less than for the 3-picoline system (N = 1280 +/- 80) st a flow rate of 0.50 +/- 0.05 mL/min and is dependent on its distribution ratio. The behavior of the Pd(II)-TOPO system in CPC can be attributed to the slow kinetics of back-extraction of the PdCl2(TOPO)2 complex. The dissociation rate constant for this complex in aqueous solution has been determined to be 168 +/- 8 M-1 s-1 by the stopped-flow kinetics procedure. This kinetic study revealed that the parameter channel equivalent of a theoretical plate (CETP), which is analogous to the reduced plate height, can be correlated to the half-life for the back-extraction and the distribution ratio of Pd(II). These findings have general application to all chromatographic separations involving metal complex formation and dissociation because reaction kinetics too fast to be observed by ordinary means will have a significant effect on chromatographic efficiency.