Study of peak shape and efficiency in butyl acrylate-based monolithic columns for capillary electrochromatography.

The study and modelling peak shape of in capillary electrochromatography (CEC), obtained using butyl acrylate (BA)-based monolithic columns, is described in this article. A modified-Gaussian model, which is a function of conventional experimental parameters: retention time (t(R)), peak height (H(0)) and standard deviation (sigma(0)) at the peak maximum, and left (A) and right (B) halfwidths, was used to describe the peaks of thiourea and several polyaromatic hydrocarbons compounds, which were eluted under several applied voltages. A mean relative error below 2% in the prediction of peak shape is obtained. Based on peak parameters, an easy and reliable estimation of global chromatographic performance, efficiency and peak capacity of BA-based monoliths was also considered. A comparison in terms of chromatographic performance of BA-based monoliths in CEC with CE mode and RPLC microparticulate columns was also performed.

Comparison of thermal- and photo-polymerization of lauryl methacrylate monolithic columns for CEC.

Lauryl methacrylate-based (LMA) monolithic columns for CEC, prepared using either thermal initiation or by UV-irradiation in the presence of AIBN have been compared. Thermal polymerization was carried out at 70 degrees C for 20 h. For UV initiation, the effects of the time exposure to UV light and irradiation energy were investigated. For each initiation process, the influence of composition of porogenic solvent (1,4-butanediol/1-propanol ratio) on the physical and electrochromatographic properties of the resulting monoliths was also evaluated. Photochemically lauryl methacrylate stationary phases initiated showed higher permeabilities and better efficiencies than those prepared by thermal initiation. After optimization of polymerization mixture, photopolymerized columns provided a permeability of 4.25 x 10(-13) m(2) and a minimum plate height of 13.4 microm for a mixture of polycyclic aromatic hydrocarbons. Similar column-to-column and batch-to-batch reproducibilities, with RSD values below 11.6 and 11.0 % for the thermal- and UV-initiated columns, respectively, were obtained.

CEC column behaviour of butyl and lauryl methacrylate monoliths prepared in non-aqueous media.

Polymeric monolithic stationary phases for capillary electrochromatography were prepared using two bulk monomers, butyl methacrylate (BMA) and lauryl methacrylate (LMA), by in situ polymerization in non-aqueous media. The effect of 1,4-butanediol/1-propanol ratio on porous properties was investigated separately for each monomer, keeping the proportion of monomers to pore-forming solvents fixed at 40:60 wt:wt. Also, mixtures of BMA and LMA at different 1,4-butanediol/1-propanol ratios were studied for tailoring the morphological features of the monolithic columns. The chromatographic performance of the different columns was evaluated by means of van Deemter plots of polycyclic aromatic hydrocarbons. Mercury-intrusion porosimetry, SEM, and nitrogen-adsorption measurements were also performed in order to understand their retention behaviour and porous properties. A comparison of these features was also performed for monoliths made with one bulk monomer (BMA or LMA) and with mixtures of both. These mixed monoliths showed satisfactory efficiencies and analysis times compared with those made with one bulk monomer; thus, the BMA-LMA monoliths constitute an attractive alternative to manipulate the electrochromatographic properties of methacrylate beds in CEC.

Chemical initiation for butyl and lauryl acrylate monolithic columns for CEC.

Butyl acrylate (BA)- and lauryl acrylate (LA)-based monolithic stationary phases for CEC were synthesized, using a redox system as initiator of polymerization. BA monoliths were initiated with ammonium peroxodisulfate, whereas LA columns were obtained with lauroyl peroxide as initiator. In both cases, TEMED was used to activate the process. The influence of porogenic solvent composition on both morphological and electrochromatographic properties of the resulting monoliths was investigated. Excellent efficiencies (minimum plate heights of 4.2-6.3 microm for BA columns and 2.6-5.3 microm for LA stationary phases, for a PAHs mixture) were achieved. The capability of separation of both types of monolithic beds was compared by the analysis of complex mixtures of polycyclic aromatic hydrocarbons and anabolic steroids.

Preparation and evaluation of butyl acrylate-based monolithic columns for CEC using ammonium peroxodisulfate as a chemical initiator.

Acrylate-ester-based monoliths for CEC using peroxodisulfate as a chemical initiator were prepared. The influence of two ternary porogenic solvents on the physical and chromatographic properties of butyl acrylate monolithic stationary phases was investigated. The composition and the ratio of porogenic solvent were adjusted to obtain highly permeable rigid monoliths with adequate column efficiency. Among the prepared butyl acrylate monoliths, those polymerized from a ternary porogenic solvent of acetonitrile/ethanol/water exhibited the most promising performance with a minimum plate height for naphthalene of 10.5 microm and a bed permeability of 7.3 x 10(-14) m(2). A comparison in terms of efficiency and permeability with thermal and UV initiation using alpha,alpha'-AIBN was also performed. The resulting monolithic stationary phases were evaluated in terms of reproducibility, giving RSD values below 5.1% in the electrochromatographic properties studied.

Lauroyl peroxide as thermal initiator of lauryl methacrylate monolithic columns for CEC.

The preparation of lauryl methacrylate (LMA)-based monolithic columns for CEC using lauroyl peroxide (LPO) as thermal initiator of polymerization has been investigated. The influence of initiator amount and composition of porogenic solvent on the physical and electrochromatographic properties of the resulting LMA-based monoliths was evaluated. A comparison with LMA-based columns thermally polymerized with AIBN was performed. At a given porogenic solvent composition, LMA stationary phases initiated with LPO showed higher permeabilities and better efficiency values than those prepared using AIBN as initiator. The optimum polymerization mixture found for LPO initiator provided a minimum plate height of 9.5 mum in a polycyclic aromatic hydrocarbon mixture. The produced monolithic beds also exhibited a good run-to-run repeatability and column-to-column and mixture-to-mixture reproducibility, with RSD values below 5.3% for the retention factors, areas and plate heights.

Preparation and characterization of hexyl methacrylate monolithic columns for CEC.

The preparation of hexyl methacrylate (HMA) monolithic columns for CEC separations has been investigated with two initiation systems: (i) ammonium peroxodisulphate and TEMED to activate the polymerization reaction, and (ii) by thermal initiation with AIBN. For both initiators, the influence of composition of porogenic solvent on morphological and chromatographic properties of monoliths was investigated. Two porogenic solvent systems, aqueous and non-aqueous media, were also studied for monolithic beds polymerized with AIBN. Under optimal conditions, low minimum plate heights (9.6 mum for peroxodisulphate, 8.4 and 10.0 mum for AIBN in aqueous and non-aqueous porogenic solvents, respectively) were obtained. A comparison in terms of chromatographic performance of HMA monoliths with butyl methacrylate columns polymerized with both initiators was also performed. The resulting HMA-based stationary phases also exhibited a good repeatability and column-to-column reproducibility, with RSD values below 5.6% in the studied electrochromatographic parameters. The potential of HMA-based columns was demonstrated by the analysis of complex mixtures of polyaromatic hydrocarbons and anabolic steroids.

Peroxodisulfate as a chemical initiator for methacrylate-ester monolithic columns for capillary electrochromatography.

Organic monolithic stationary phases for CEC were synthesized in situ in fused-silica capillaries. Polymerization mixtures were composed of butyl methacrylate, ethylene dimethacrylate, and [2-(methacryloyloxy)ethyl]trimethyl ammonium chloride in the presence of a porogenic solvent, using ammonium peroxodisulfate as chemical initiator, and N,N,N',N'-tetramethylethylenediamine to activate the reaction. The influence of the amount of initiator, temperature, and composition of porogenic solvent on the physical and chromatographic properties of monolithic stationary phases has been investigated. A minimum plate height of 14.5 microm was obtained at 18 wt% of 1,4-butanediol in the polymerization mixture. The produced monolithic stationary phases exhibited a good repeatability and batch-to-batch and mixture-to-mixture reproducibility, with RSD values below 5.6% in the electrochromatographic parameters studied. A comparison with columns prepared by thermal initiation with alpha,alpha'-azobisisobutyronitrile (AIBN) was also performed. The most efficient column initiated with peroxodisulfate showed better efficiencies and selectivities than that prepared with AIBN at the same composition mixture.