Mixed-mode reversed-phase and ion-exchange monolithic columns for micro-HPLC.
ABSTRACT This paper describes the fabrication of RP/ion-exchange mixed-mode monolithic materials for capillary LC. Following deactivation of the capillary surface with 3-(trimethoxysilyl)propyl methacrylate (gamma-MAPS), monoliths were formed by copolymerisation of pentaerythritol diacrylate monostearate (PEDAS), 2-sulphoethyl methacrylate (SEMA) with/without ethylene glycol dimethacrylate (EDMA) within 100 microm id capillaries. In order to investigate the porous properties of the monoliths prepared in our laboratory, mercury intrusion porosimetry, SEM and micro-HPLC were used to measure the monolithic structures. The monolithic columns prepared without EDMA showed bad mechanical stability at high pressure, which is undesirable for micro-HPLC applications. However, it was observed that the small amount (5% w/w) of EDMA clearly improved the mechanical stability of the monoliths. In order to evaluate their application for micro-HPLC, a range of neutral, acidic and basic compounds was separated with these capillaries and satisfactory separations were obtained. In order to further investigate the separation mechanism of these monolithic columns, comparative studies were carried out on the poly(PEDAS-co-SEMA) monolithic column and two other monoliths, poly(PEDAS) and poly(PEDAS-co-2-(methacryloyloxy)ethyl-trimethylammonium methylsulphate (METAM)). As expected, different selectivities were observed for the separation of basic compounds on all three monolithic columns using the same separation conditions. The mobile phase pH also showed clear influence on the retention time of basic compounds. This could be explained by ion-exchange interaction between positively charged analytes and the negatively charged sulphate group.
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ABSTRACT: New affinity monolithic capillary columns of 150 µm internal diameter were prepared in situ fused glass capillary via either immobilization or encapsulation of Candida antarctica lipase B (CALB) on or within polymer monoliths, respectively. The immobilized lipase-based monoliths were prepared via copolymerization of 19.1% monomers (8.9% MMA and 10.2% GMA), 19.8% EDMA, and 61.1% porogens (54.2% formamide and 6.9% 1-propanol) w/w or 20% GMA, 20% EDMA, and 60% porogens (51.6% cyclohexanol and 8.4% 1-dodecanol) in the presence of AIBN (1%) as a radical initiator. This was followed by pumping a solution of lipase through the capillaries and rinsing with potassium phosphate buffer. On the other hand, the encapsulated lipase-based monoliths were prepared via copolymerization of 20% monomers (GMA), 20% EDMA, and 60% porogens (48% 1-propanol, 6% 1,4-butanediol) or 16.4% monomers (16% BuMA, 0.4% SPMA), 23.6% EDMA, and 60% porogens (36% 1-propanol, 18% 1,4-butanediol along with 6% lipase aqueous solution in potassium phosphate buffer. The prepared capillary columns were investigated for the enantioselective nano liquid chromatographic separation of a set of different classes of racemic pharmaceuticals, namely, α- and β-blockers, antiinflammatory drugs, antifungal drugs, dopamine antagonists, norepinephrine-dopamine reuptake inhibitors, catecholamines, sedative hypnotics, diuretics, antihistaminics, anticancer drugs, and antiarrhythmic drugs. Run-to-run repeatability was quite satisfactory. The encapsulated lipase-based capillary monolith showed better enantioselective separations of most of the investigated compounds. Baseline separation was achieved for alprenolol, atenolol, bromoglutithimide, carbuterol, chloropheneramine, cizolertine carbinol, 4-hydroxy-3-methoxymandelic acid, desmethylcizolertine, nomifensine, normetanephrine, and sulconazole under reversed phase chromatographic conditions. A speculation about the understanding of the chiral recognition mechanism of lipase-based monoliths toward the investigated pharmaceuticals is discussed. Chirality 00:000–000, 2014. © 2014 Wiley Periodicals, Inc.Chirality 03/2014; · 1.72 Impact Factor
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ABSTRACT: The separations of small molecules using columns containing porous polymer monoliths invented two decades ago went a long way from the very modest beginnings to the current capillary columns with efficiencies approaching those featured by their silica-based counterparts. This review article presents a variety of techniques that have been used to form capillary formats of monolithic columns with enhanced separation performance in isocratic elutions. The following text first describes the traditional approaches used for the preparation of efficient monoliths comprising variations in polymerization conditions including temperature as well as composition of monomers and porogenic solvents. Encouraging results of these experiments fueled research of completely new preparation methods such as polymerization to an incomplete conversion, use of single crosslinker, hypercrosslinking, and incorporation of carbon nanotubes that are described in the second part of the text.Journal of Chromatography A 07/2011; 1228:250-62. · 4.61 Impact Factor
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ABSTRACT: 2,3,6-Tris(phenylcarbamoyl)-β-cyclodextrin-6-methacrylate was prepared and used as a functional monomer for the preparation of new β-cyclodextrin (β-CD) functionalized polymer monoliths. The polymer monoliths were prepared via the copolymerization of β-CD methacrylate and ethylene glycol dimethacrylate in different ratios in situ in fused silica capillary (internal diameter 150μm). The effect of functional monomer/cross linker concentration on the chiral separation of different classes of pharmaceuticals namely; α- and β-blockers, antiinflammatory drugs, antifungal drugs, dopamine antagonists, norepinephrine-dopamine reuptake inhibitors, catecholamines, sedative hypnotics, diuretics, antihistaminics, anticancer drugs and antiarrhythmic drugs was investigated. Baseline separation was achieved for propranolol, ifosfamide, alprenolol, tertalol, 1-indanol, tebuconazole, o-methoxymandelic acid, celiprolol and cizolertine under reversed phase conditions with mobile phase composed of methanol and water, using nano liquid chromatography. The method provides more economical analysis under environmentally benign conditions. The prepared capillary columns showed good mechanical stability and good repeatability (run-to run and batch-to batch).Journal of Chromatography A 04/2014; · 4.61 Impact Factor