ELECTROSTATIC INTERACTIONS BETWEEN RU(BPY)(3)(2+) AND CHROMATOGRAPHICSURFACES

In HPLC, the zones of organic bases tail when silica-based stationary phases are used because the analytes and the surface are oppositely ch arged. In developing new stationary phases to achieve lower surface ch arge, a measure of surface charge is needed. The choice of a suitable. analyte to quantitate electrostatic interactions is complicated by th e acid-base equilibrium of the analyte itself and by nonelectrostatic interactions between the analyte and the surface, which alter the char ge-induced tailing. This paper describes the study of the pH dependenc e of adsorption to isolate electrostatic interaction and the use of a cationic probe, tris(2,2'-bipyridine)ruthenium chloride (Ru(bpy)(3)(2)), to sense surface charge without the complication of the probe's ac id-base equilibria. The paper further describes the application of Gou y-Chapman theory to reveal the surface charge density. The results con firm that type A silica is considerably more acidic than type B silica and that horizontal polymerization makes type A silica perform as wel l as type B silica.