Immobilization of stationary liquids in reversed- and normal-phase liquid chromatography : Production and testing of materials for bonded-phase chromatography

New types of silanization reagents for small-particle silica packing materials and a solventless vacuum technique for carrying out the reaction were tested with the aim of conveniently achieving a more complete reaction of the silanol groups. Materials for bonded-phase chromatography with better quality and reproducibility were obtained. In a second series of experiments we attempted to fix monomeric and oligomeric siloxanes and also certain unsaturated hydrocarbons on either unsilanized or presilanized materials by cross-linking reactions with γ-radiation or peroxides. With the presilanized materials of the Si-O-Si(CH3)3 type we obtained better surface deactivation and fixation of the siloxane oligomers on the surface alkylsilyl groups by the cross-linking reaction. All silicas should be examined for particle size and structure before and after chemical treatment and analysed for carbon content in bulk and in the surface layer, for permeability and for tailing behaviour after packing of a column. Surface area determinations are also advisable. Chromatographic measurements for efficiency and polarity (selectivity) gave information about the practical value of these materials

Syntheses of stationary phases for reversed-phase LC using silanization and polymer coating

Various methods and reagents for silanization of silicas originating from different manufacturers were investigated in comparison to the method published by the authors which makes use of an enolate of acetylacetone. This reagent proved to be highly reactive. New types of reversed phase materials were also synthesized by polymer coating applying crosslinking and chemical bonding to the surfaces of silica and alumina. In this work dicumyl peroxide and azo-t-butane were used for radical generation. The reversed phase materials obtained with alumina can be used for separations at PH-values up to 12. Silica materials begin to already be deteriorated at a PH-value of 8

Immobilization of stationary liquids on silica particles by γ-radiation

Continuing our work on new silanization reagents for producing chemically-modified small-particle, silica support material exhibiting improved chromatographic performance and especially good shielding of silanol groups in respect of solute-stationary phase interaction, we have developed new silica-based polymer phases with different “polarities” by crosslinking or polymerization reactions induced by γ-radiation. Polybutadienes or polysiloxanes were immobilized on non-, or specially presilanized, 5μm silica particles by using different dose-rates of γ-radiation and by addition of different amounts of allylmethacrylate as a radical stabilizer. The materials obtained were tested by elemental analysis, scanning electron microscopy, ESCA and IR-reflexion measurements as well as by chemical Si−OH determinations. Chromatographic testing has been carried out with different, especially strongly basic solutes, under normal and reversed phase conditions. The dual retention mechanism model of Nahum and Horvath [1] was applied to the usual commercially available phases and those phases produced by ourselves. The influences of mobile phase additives such as acetonitrile or tetrahydrofuran were also investigated following the chromatographic test procedures for characterization of the support materials synthesized. The silicas obtained show excellent long term stability to all types of HPLC solvents. Their inertness with respect to irreversible adsorption of polar, especially basic, compounds can only be compared with that of reticular bulk polymer stationary phases without any silica skeleton. Unlike pure polymer particles these materials exhibit high pressure stability, only moderate shrinking and swelling effects, and most importantly, high plate numbers, comparable with normal brushtype stationary phases