New data on the sorption properties of alpha(1)-acid glycoprotein chiral stationary phase

A binding study on alpha(1)-acid glycoprotein (AGP), a widely used chiral s tationary phase in drug analysis, has been performed. Being a selectivity d ecisive factor in enantiomer separation, the adsorption of the organic modi fiers, as the regularly used acetonitrile (AcCN) and also of dioxane, was d etermined from phosphate buffer eluents (pH 7.2 and 4.0) in the concentrati on range of 0.57-3.81 M and 0.11-1.9 M, respectively. The adsorbed amount w as determined by gas chromatography. At lower modifier concentrations no si gnificant difference was found in the binding extent of AcCN and dioxane. A t higher, characteristic concentrations of the organic additives, a saturat ion was obtained at both pH values; furthermore, at pH 4.0 it was followed by a definite rise in the modifier adsorption. This particular behaviour ma y indicate the exposure of new binding sites on AGP surface, as a result of changes in the protein structure, which was confirmed by CD-spectroscopic measurements. The pH dependence of binding in equimolar concentration (1.9 M) has shown the priority of dioxane at PPI 4.0, while the adsorption of Ac CN dominated at higher pH, indicating the different character of the two so lvents. The increased hydrogen bond formation should cause the preferred ad sorption of dioxane at pH 4.0. Chirality 11:212-217, 1999. (C) 1999 Wiley-L iss, Inc.