Adsorption equilibria and overloaded band profiles of basic drugs in a reversed-phase system

Single-solute adsorption equilibrium isotherms of three basic drugs: buspir one, doxepin and diltiazem were determined by frontal analysis in a reverse d-phase system composed of an octadecylsilica packing material and a buffer ed mobile phase containing acetonitrile. The adsorption data were fitted to the bi-langmuir model. Within the framework of this model, the adsorption of the drugs is assumed to occur on two distinct kinds of sites with differ ent average adsorption energies. The data are consistent with the assumptio n that the low energy sites account for the hydrophobic interactions betwee n the solutes and the chemically bonded alkyl chains and the high energy si tes account for the ion-exchange interactions between the residual active s ilanols and the protonated bases. Multisolute, overloaded band profiles wer e also measured for the three binaries and for mixtures of the three drugs. Theoretical band profiles were calculated using the equilibrium dispersive model and the ideal adsorbed solution theory model which uses the paramete rs determined from the correlation of the single-solute adsorption data. Go od agreement was found between the experimental and calculated overloaded b and profiles. (C) 2000 Elsevier Science B.V. All rights reserved.