Study of a polymer immobilized on silica gel as stationary phase for chiral liquid chromatography

Preparation and characterisation of poly(vinyl alcohol)/cyclodextrin microspheres as matrix for inclusion and separation of drugs

Poly(vinyl alcohol) (PVA) microspheres containing cyclodextrin (CD) were obtained by chemical cross-linking with glutaraldehyde of an acidified mixture solution of PVA and alpha-, beta- or gamma-CD. The amount of linked CD in microspheres, estimated by tetrazolium blue method, decreases in the order beta- > gamma- > alpha-CD. The dimensions of PVA/gamma-CD microspheres are much higher than those of PVA/alpha- and beta-CD. The cross-linking density of microspheres was estimated by the amount of iodine retained by the polymer matrix. The pore size as well as the porous volume of PVA/CD microspheres decrease significantly on increasing the amount of glutaraldehyde, but are enough large to permit the access of drugs to the CD cavity. In order to test the PVA/CD microsphere inclusion ability, the microspheres were packed in a glass column and the liquid chromatographic behaviour by isocratic elution of different drugs or typical organic compounds, taken as model drugs, was investigated.

Study of the retention properties of warfarin enantiomers on a beta-cyclodextrin polymeric support

High-performance liquid chromatography was used to study the retention properties of (R)- and (S)-warfarins on a silica support coated with a beta-cyclodextrin polymer. The influence of the methanol content of the acetate buffer eluent was investigated at pH 4. The measure of the variations of retention time with temperature enables one to determine the enthalpy and the entropy of adsorption. The plot of the two thermodynamic functions shows a minimum around 30% (v/v) methanol. At low methanol contents, the decrease of the hydrophobic interactions with increasing methanol content explains the decrease of the enthalpic and entropic terms. Above 40% (v/v) methanol, the decrease of the adsorption enthalpy absolute value is due to the solvation by the organic component. From the analysis of peak shape in mass-overload conditions, the column capacity toward each enantiomer was determined. A lower capacity was found toward (S)-warfarin, the more retained enantiomer. Peak shape analysis in mass-overload conditions was used to determine the adsorption isotherm. A Langmuir-type adsorption isotherm accounts well for the experimental data.

The design of chiral separation media using monodisperse functionalized macroporous beads: effects of polymer matrix, tether, and linkage chemistry

Porous size monodisperse methacrylate beads containing amino and hydroxyl groups, which can be used as a platform for the production of chiral separation media, have been prepared using the staged templated suspension polymerization process. The monomers 2-hydroxyethyl methacrylate and several tert-butoxycarbonyl-protected aminoalkyl methacrylates were used for the preparation of both hydroxyl- and amino-functionalized beads. Attachment of a chiral selector based on L-valine-3,5-dimethylanilide through a carbamate and a urea linkage, respectively, provides chiral stationary phases with excellent enantioselectivities in the separation of the enantiomers of 3,5-dinitrobenzamido derivatives of alpha-amino acids. For comparison purposes, a separation medium was also prepared by the direct polymerization of a chiral monomer analogous to the hydroxyethyl methacrylate-based stationary phase. The chiral stationary phases prepared with the N-methyl-2-aminoethyl methacrylate platform exhibit the best selectivity, and separation factors as high as 15 were achieved under normal-phase HPLC conditions.

Polymer- versus silica-based separation media: elimination of nonspecific interactions in the chiral recognition process through functional polymer design

A novel chiral stationary phase that contains a new chiral selector based on L-valine-3,5-dimethylanilide attached to monodisperse poly(glycidyl methacrylate-co-ethylene dimethacrylate) beads has been prepared. The polymeric separation medium provides greatly enhanced enantioselectivities and reduced retention times when compared to the analogous silica-based chiral stationary phase in the separation of the enantiomers of 3,5-dinitrobenzamido derivatives of alpha-amino acids under normal-phase HPLC conditions. Separation factors (alpha) of up to 7 were achieved with the polymeric separation medium, which is also useful for the separation of large samples under overload conditions.