Hydrolyzed Vinyl Acetate–Divinylbenzene Copolymer Microspheres Containing L -Proline for Chiral Separation of Amino Acids

Abstract

A new packing material for ligand-exchange chromatography, L -proline-modified hydrolyzed vinyl acetate-divinylbenzene copolymer microspheres, has been prepared and evaluated. The microspheres, prepared by a one-step swelling and polymerization method, have a narrow bead size (as determined by scanning electron microscopy, SEM), a broad pore-size distribution (by nitrogen adsorption) and, especially, inhomogeneous structural composition (by differential scanning calorimetry). The support, which has an L -proline content of 0.35 mmol g⁻¹ (nitrogen analysis), provides good enantioselectivity and column efficiency. Twenty-three of the twenty-four common D ,L -amino acids tested were resolved on a 250 mm × 4.6 mm i.d. column and mixtures of up to seven racemic amino acids were easily separated into their enantiomers. Two average pore diameters, volume-average (d_v) and surface-average (d_s) pore diameters, are defined. The ratio d_v/d_s is used to characterize the broadness of the pore-size distribution. It is shown that the widely used formula d=4V_p/S for cylindrical pores, where V_p is pore volume and S the specific surface area, gives the surface-average pore diameter.