Monolithic capillary columns consisting of poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) and their diol derivatives with incorporated hydroxyl functionalized multiwalled carbon nanotubes for reversed-phase capillary electrochromatography

Abstract

Two types of monolithic stationary phases with incorporated hydroxyl functionalized multiwalled carbon nanotubes (OH-MWCNTs) were introduced and evaluated, namely, the poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) monolith, denoted as poly(GMA-co-EDMA), and a diol derivative of the poly(GMA-co-EDMA) monolith. The diol derivative monolith was obtained by subjecting the poly(GMA-co-EDMA) monolith with physically incorporated OH-MWCNTs to an acid treatment with 0.1 M sulfuric acid at a moderate temperature of 50 °C for a total of 7.5 h. Also, the poly(GMA-co-EDMA) monolith with both physically and covalently incorporated OH-MWCNTs was prepared by subjecting the physically incorporated monolithic column to a Lewis acid catalyzed reaction in the presence of BF₃ in order to react some of the OH-MWCNTs with the epoxy rings of the poly(GMA-co-EDMA) monolith. In all cases, the OH-MWCNTs were subjected to high power sonication at an output power of 10 W for 15 min with the aim of better dispersing the incorporated nanotubes into the monoliths under investigation. In fact, high power sonication yielded columns with a relatively higher plate count (∼2 fold increase) when compared to low power sonication. While the incorporation of OH-MWCNTs into the poly(GMA-co-EDMA) monolith acted as an amendment boosting the nonpolar character of the monolith and providing additional π–π interactions, the diol derivative monolith with its polar backbone character acted nearly as a support for the OH-MWCNT stationary phase giving rise to a carbon nanotube sorbent providing hydrophobic and π–π interactions via the incorporated OH-MWCNTs. These two kinds of columns were evaluated using alkylbenzenes, toluene derivatives, aniline compounds, phenols and polyaromatic hydrocarbons.