Development of capillary electrochromatography with poly(styrene-divinylbenzene-vinylbenzenesulfonic acid) monolith as the stationary phase (original) (raw)
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Journal of Chromatography A, 2006
Methacrylate-ester-based monoliths containing quaternary ammonium groups were prepared in situ in capillary columns and in simultaneous experiments in vials, employing thermal initiation. The chromatographic properties of the monoliths were determined with capillary electrochromatography (CEC), and their morphology was studied with mercury-intrusion porosimetry on the bulk materials. Materials with different, well repeatable pore-size distributions could be prepared. A satisfactory column-to-column and run-to-run repeatability was obtained for the electro-osmotic mobility, the retention characteristics (k-values) and the efficiency on the columns prepared and tested in the CEC mode. A relatively high electro-osmotic flow was observed in the direction of the positive electrode. The electroosmotic mobility was found to be influenced only marginally by mobile-phase parameters such as the pH, ionic strength, and acetonitrile content. The retention behavior of the monolithic columns was similar to that of columns packed with C 18 -modified silica particles. Columns could be prepared with optimum plate heights ranging from 6 m for unretained compounds to 20 m for well retained (k = 2.5) polyaromatic hydrocarbons. However, for specific analytes a -still unexplained -lower chromatographic column efficiency was observed.
Microchemical Journal, 2013
Monolithic poly(octadecyl methacrylate-co-ethylene dimethacrylate) capillary columns for use in capillary electrochromatography (CEC) were developed and characterized by porosimetric measurements and scanning electron microscopy (SEM). The stationary phases were prepared using 2-acryloylamido-2-methylpropanesulfonic acid (AMPS) as the ionizable monomer and 2,2′-azobisisobutyronitrile (AIBN) as the initiator of thermal polymerization, which occurred at 60°C. The porogenic solvents used in this work were amyl alcohol and 1,4-butanediol, in the proportion 65:35 (v/v). The ratio between monomers and porogenic solvents was varied in a range of 60 to 80% (v/v) of porogenic agents. The porosimetry showed that the increase in content of porogenic solvents caused an increase in pore surface area, but a relationship with the separation efficiencies was not observed. SEM agreed with the conclusions made through porosimetry, where decreases in globule size could be noted with increases in porogenic solvents.
ELECTROPHORESIS, 2001
Separation of basic, acidic and neutral compounds by capillary electrochromatography using uncharged monolithic capillary columns modified with anionic and cationic surfactants A mode of capillary electrochromatography (CEC), based on the dynamical adsorption of surfactants on the uncharged monolithic stationary phases has been developed. The monolithic stationary phase, obtained by the in situ polymerization of butyl methacrylate with ethylene dimethacrylate, was dynamically modified with an ionic surfactant such as the long-chain quaternary ammonium salt of cetyltrimethylammonium bromide (CTAB) and long-chain sodium sulfate of sodium dodecyl sulfate (SDS). The ionic surfactant was adsorbed on the surface of polymeric monolith by hydrophobic interaction, and the ionic groups used to generate the electroosmotic flow (EOF). The electroosmotic mobility through these capillary columns increased with increasing the content of ionic surfactants in the mobile phase. In this way, the synthesis of the monolithic stationary phase with binary monomers can be controlled more easily than that with ternary monomers, one of which should be an ionic monomer to generate EOF. Furthermore, it is more convenient to change the direction and magnitude of EOF by changing the concentration of cationic or anionic surfactants in this system. An efficiency of monolithic capillary columns with more than 140 000 plates per meter for neutral compounds has been obtained, and the relative standard deviations observed for t 0 and retention factors of neutral solutes were about 0.22% and less than 0.56% for ten consecutive runs, respectively. Effects of mobile phase composition on the EOF of the column and the retention values of the neutral solutes were investigated. Simultaneous separation of basic, neutral and acidic compounds has been achieved.
Journal of Chromatography A, 1999
The effect of methanol and acetonitrile, respectively, on the separation of neutral compounds (benzyl alcohol, phenols) is investigated in electrokinetic chromatographic (EKC) systems consisting of polyethyleneimine (PEI) as charged, polymeric, replaceable pseudostationary phase. The separation systems consist of a buffer solution (2-morpholinoethanesulfonic acid, pH 7.0, 20 mM) containing 0.3-0.9% (w / v) PEI as additive and a varying percentage of methanol (0-50%, v / v) or acetonitrile (0-30%, v / v). EKC is carried out in fused-silica capillaries [47.0 cm (effective length 40.3 cm)3100 mm I.D.]. They are dynamically coated with PEI, resulting in an electroosmotic flow directed towards the anode. The neutral analytes are migrating with the electroosmotic flow, and are retarded by the electrically driven counterflow of PEI. Separation of the analytes follows in the sequence benzyl alcohol, phenol, resorcinol, pyrogallol, reflecting the increasing hydrogen bond acidity and polarity (polarizibility) of the solutes. However, addition of methanol or acetonitrile causes a drastic loss of resolution, whereby the relative retention of the separands (related to benzyl alcohol) indicates a decrease of retardation upon addition of the organic solvents.
Journal of Chromatography A, 2010
In this study, a series of poly(divinylbenzene-alkyl methacrylate) monolithic stationary phases, which were prepared by single step in situ polymerization of divinylbenzene and various alkyl methacrylates (butyl-, octyl-, or lauryl-methacrylate), were developed as separation columns of benzophenone compounds for capillary electrochromatography (CEC). In addition to the presence of plenty of benzene moieties, the stationary phases contained long and flexible alkyl groups on the surface. With an increase in the molecular length of alkyl methacrylate, the polymeric monolith, which had higher hydrophobicity, effectively reduced the peak tailing of benzophenones, but a weaker retention was observed. The unusual phenomenon was likely due to theinteraction between the aromatic compound and the polymeric material. The usage of longer alkyl methacrylate as reaction monomer limited the retention of aromatic compounds on the stationary phase surface, thus theinteraction between them was possibly reduced. Consequently, the retention time of aromatic compounds was markedly decreased with an increase in carbon length of alkyl methacrylate that was carried on the polymeric monolith. Compared to previous reports on polystyrene-based columns in which the peak-tailing problem was reduced by decreasing the benzene moieties on the stationary phase, this study demonstrated that the undesirable retention (peak-tailing) could also be improved by the inclusion of long alkyl methacrylate to the polystyrene-based columns.
Analytical Chemistry, 2000
A permanent polycation, polydiallyldimethylammonium (PDADMA), is applied as a linear, polymeric, replaceable, and nonmicellar pseudostationary phase for the separation of neutral analytes by capillary electrokinetic chromatography. It is shown that this polymer used in the background electrolyte is able to separate the analytes even if it does not form micelles under the given conditions. The most favorable aspect for practical use lays in the simple replacement of the separation media after each run, thus generating highly reproducible conditions. To determine the capacity factors of the analytes, a new method, based on an isotachophoretic regime, has been introduced for the measurement of the electrophoretic mobility of the polymeric pseudo-stationary phase. The capacity factors in the separation system, derived from the mobilities of the polymer, the electroosmotic flow, and the mobilities of 15 individual aromatic analytes, range between 0.3 and 1.2 for the given separation media (aqueous solution of acetate buffer, pH 5.2, with 4% w/w PDADMA). The type of interaction in the pseudochromatographic system was clarified from solvation parameters based on the linear free energy relationship model. It was found that π and n electron interactions and hydrogen-bond basicity of the polymer, as compared with the aqueous bulk phase, are the main cause of retention of the analytes.
Journal of Chromatography A, 2011
A very simple and readily performed method is described for the preparation of poly(styrenedivinylbenzene-methacrylic acid) monolithic columns for capillary liquid chromatography. The effect of the methacrylic acid content on the morphological and chromatographic properties has been investigated. Methacrylic acid is shown to be essential for isocratic separations of small organic analytes by capillary liquid chromatography. Column efficiencies of about 28,000 theoretical plates/m have been obtained for all the test compounds. The batch-to-batch and run-to-run repeatability of the retention times is better than 1.5%.
Monolithic organic polymeric columns for capillary liquid chromatography and electrochromatography
Journal of Chromatography B, 2006
This review briefly summarizes the present state of the preparation and use of capillary monolithic columns for liquid chromatography (LC) and electrochromatography (EC). Most important approaches to the preparation of monolithic stationary phases based on organic polymers are outlined and the properties of the monoliths obtained are compared with those of classical particulate phases. A few selected applications of monolithic columns are shown to demonstrate the most important advantages of monolithic capillary columns. It is concluded that both the monolithic and particulate capillary columns are important and that judicious choice of the type suitable for a particular application requires careful consideration of the purpose of the separation and the properties of the solutes to be separated. Monolithic columns are substantially younger than packed ones and thus will require further theoretical and experimental study to further improve their preparation and to enable reliable prediction of their properties and applicability; nevertheless, they are very promising for the future.
Journal of Chromatographic Science, 2012
Butyl methacrylate (BMA)-ethylene dimethacrylate (EDMA)-methacrylic acid (MAA) and BMA-EDMA-2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) monolithic columns were prepared by varying the percentage of ionic monomers for capillary electrochromatography. Monolithic columns with a higher content of ionic monomers provided better column efficiency, and the performance of BMA-EDMA-MAA monoliths was better than BMA-EDMA-AMPS. To characterize and optimize BMA-EDMA-MAA monoliths, the effects of the content of cross-linker and the total monomer in the polymerization mixture on column performance were also studied. Plate heights of 8.2 mm for the unretained solute (thiourea) and 12.6 mm for the retained solute (naphthalene) were achieved with a monolithic column using 2.5% MAA (Column I).
Polymer, 2010
Porous polystyrene-based monolithic columns were engineered through the in-situ generation of poly (3-caprolactone) (PCL)/polystyrene (PS) semi-interpenetrating polymer networks (semi-IPNs), followed by the extraction of the uncrosslinked partner acting as a polymeric porogen. In a first stage, the semi-IPNs were prepared within the confines of fused silica capillaries by UV-initiated free-radical copolymerization of styrene and divinylbenzene, in the presence of PCL oligomers. In a second stage, the quantitative extraction of uncrosslinked oligoesters led to the formation of porous frameworks with a hierarchical porosity, as evidenced by SEM and DSC-based thermoporometry. Such as-obtained porous monoliths could be efficiently used as reversed-phase stationary phases for the separation of alkyl benzene derivatives by capillary electrochromatography (CEC).