Capillary electrochromatography with polyacrylamide monolithic stationary phases having bonded dodecyl ligands and sulfonic acid groups: Evaluation of column performance with alkyl phenyl ketones and neutral moderately polarpesticides

In this report, we describe the preparation of porous polyacrylamide-based monolithic columns via vinyl polymerization. These monoliths possess in the ir structures bonded dodecyl ligands and sulfonic acid groups. While the su lfonic acid groups are meant to support the electroosmotic flow (EOF) neces sary for moving the mobile phase through the monolithic capillary, the dode cyl ligands are introduced to provide the nonpolar sites for chromatographi c retention. However, incorporating the sulfonic acid groups in the monolit hs does not only support the EOF but also exhibit hydrophilic interaction w ith moderately polar compounds such as urea herbicides and carbamates insec ticides. Consequently, mixed-mode (reversed-phase/normal phase) retention b ehavior is observed with neutral and moderately polar pesticides. The amoun t of sulfonic acid group in the monolith can be conveniently adjusted by ch anging the amount of vinylsulfonic acid added to the polymerization reactio n. Optimum EOF velocity and adequate chromatographic retention are obtained when 15% vinylsulfonic acid is added to the reaction mixture. Under these conditions, rapid separation and high plate counts reaching greater than 40 0 000 plates/m are readily obtained.