Comparison on photo-initiators for the preparation of methacrylate monolithic columns for capillary electrochromatography.

The synthesis of lauryl methacrylate monoliths for capillary electrochromatography by UV polymerization using several free-radical initiators (alpha,alpha'-azobisisobutyronitrile, 2,2-dimethoxy-2-phenylacetophenone, dibenzoyl peroxide (BPO) and lauroyl peroxide (LPO)) has been investigated. Using a 1,4-butanediol/1-propanol mixture as porogenic solvent, the influence of each initiator and its content on the morphological and electrochromatographical properties of beds was evaluated. Under their respective optimum content, satisfactory separations of a test mixture of PAHs with similar efficiencies (minimum plate heights of 8.0-12.7 microm obtained from Van Deemter plots) were achieved for the four investigated photo-initiators. The columns photo-polymerized with LPO provided the best compromise between chromatographic performance and analysis time. Moreover, this initiator showed a fine control in the column retention properties. The resulting monolithic columns exhibited a good run-to-run repeatability in the tested chromatographic parameters (RSD<2.4%) for all initiators investigated; and satisfactory column-to-column repeatability (RSD<6.0%), except for beds photo-polymerized with BPO (RSD<10.8%).