Immobilization of stationary liquids on silica particles by γ-radiation

Summary

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.