Capillary columns for reversed-phase CEC prepared via surface functionalization of polymer monolith with aromatic selectors.

Macroporous crosslinked organic polymers based on N-acryloxysuccinimide (NAS) and ethylene dimethacrylate (EDMA) were prepared in the confines of 75 μm id fused-silica capillaries by photoinitiated free radical copolymerization in the presence of 2-2'-azobisisobutyronitrile as initiator and toluene as porogen. Monoliths with good mechanical strength, large porosity as well as surface reactive sites (succinimide leaving groups) could be obtained. Nucleophilic aromatic derivatives, namely benzylamine, phenylbutylamine and naphthylamine were grafted on the monolith surface to introduce π-conjugated ligands to develop particular selectivity. Successful achievement of the post-copolymerization functionalization was ascertained on the basis of in situ chemical characterization by means of Raman spectroscopy. Electrochromatographic properties of π-functionalized poly(NAS-co-EDMA) regarding alkylbenzenes, polycyclic aromatic hydrocarbons, anilines and phenols were evaluated in terms of retention, selectivity and resolution. The as-designed monolithic columns exhibited π-π interaction in addition to hydrophobic interaction due to the aromatic and non-polar nature of the surface-grafted aromatic selectors. One of the major results of this study is that monolithic columns with mixed selectivity providing high potentiality for the separation of solutes with varied chemical structure variation can be obtained by the surface grafting of the appropriate selector. Herein, an example is given for the phenylbutylamine functionalized poly(NAS-co-EDMA) where the butyl and phenyl fragments afford enhanced hydrophobic and π-selectivity, respectively.