RESUMEN
Short-term polymerization or the so-called low-conversion polymerization was applied for the preparation of N-vinylcarbazole (NVC) and 1,4-divinylbenzene (DVB) monolithic capillary columns. The synthesis was carried out by thermally initiated free radical copolymerization under the influence of inert micro- (toluene) and macroporogen (1-decanol) and α,α'-azoisobutyronitrile (AIBN) as radical initiator. The morphological and porous properties were studied by scanning electron microscopy (SEM), nitrogen adsorption, and mercury intrusion porosimetry (MIP). The copolymerization process was studied by monomer conversion measurements. This approach led to increased porosity and specific surface area. A specific surface area above 400 m(2)/g of the monolith and a distinct bimodal pore size distribution were obtained. The chromatographic performance was determined in terms of theoretical plate heights and number of theoretical plates. The lowest plate height value was found to be 3.9 µm (corresponding to ≈256,000 plates per meter) applying methylparaben utilizing an 80 mm × 0.2 mm i.d. monolithic capillary. The developed NVC/DVB monolithic supports showed high separation efficiency towards small molecules, which was exemplified applying reversed-phase (RP) separation of alkylbenzenes, beta-blockers, flavanoids, parabens, and phenones. The loading capacity was analyzed for isocratic separation of seven alkylbenzenes and was found to be up to 77 ng total mass of alkylbenzenes. Furthermore, a long-term stability test of 1,000 consecutive runs was performed and resulted in a maximum variance of 0.97, 0.85, and 0.16 % RSD for resolution, peak width at half height, and retention times, respectively. The material was proven to have a high permeability of 1.11E-14 m(2), applying water as a mobile phase.
RESUMEN
Monolithic capillary columns were prepared by thermally initiated free radical copolymerization of N-vinylcarbazole (NVC) and 1,4-divinylbenzene (DVB) within the confines of 200 and 100 µm i.d. fused silica capillaries. The reaction was carried out under the influence of inert micro-(toluene) and macroporogen (1-decanol) and α,α'-azoisobutyronitrile (AIBN) as a free radical initiator. The material proved high mechanical stability applying water and acetonitrile as mobile phases. The morphological and porous properties were studied by scanning electron microscopy (SEM), nitrogen sorption (BET) and mercury intrusion porosimetry (MIP). The homogeneity of the copolymerization process was confirmed by elemental analysis and monomer conversion measurements. The newly developed NVC/DVB monolithic supports showed high separation efficiency towards biomolecules, applying reversed-phase (RP) and ion-pair reversed-phase (IP-RP) separation modes, which is exemplified by the separations of peptides, proteins and oligonucleotides. Furthermore the maximum loading capacity was evaluated. The chromatographic performance under isocratic elution was determined in terms of theoretical plate number and plate height, where up to 41,000 plates per column and a minimum plate height value of 1.7 µm were achieved, applying oligonucleotide separations. In gradient elution mode, peak capacities of 96 and 127 were achieved within a gradient time window of 60 min for protein and oligonucleotide separations, respectively. The material proved to have high permeability, good repeatability of the fabrication process and high surface areas in the range of 120-160 m(2) g(-1).