Preparation of monolithic columns with target mesopore-size distribution for potential use in size-exclusion chromatography

Poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) Monolith with Dual Porosity for Size Exclusion Chromatography

The use of polymeric monoliths as stationary phases for liquid chromatography has been limited, despite their ability to enhance the convection flow of the mobile phase with respect to particulate-based columns. This is due to a poor balance between the volume of flow through pores and the number of active sites within polymeric monoliths. In this paper, we present the obtainment of poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) (P(GMA-co-EDMA)) monoliths with dual pore size distributions (with pore sizes of 60 and 550 nm). Hierarchical pore size distributions were achieved by performing the monolith synthesis by reversible addition-fragmentation chain transfer (RAFT) polymerization as well as using ternary porogen mixtures (containing PEG, dodecanol, and dioxane). While the controlled polymerization mechanism promoted mesopores in the monolith, ternary porogen mixtures allowed the formation of macropores. The monoliths obtained were used as stationary phases for size exclusion chromatography (SEC) for the separation of poly(methyl methacrylate) standards with molar masses between 2.50 × 103 and 3.06 × 106 g/mol, allowing selectivities that were comparable with commercially available SEC columns packed with porous particles. We believe the approach presented in this work could be the first step toward the obtainment of stationary phases for SEC with enhanced accessibility of exclusion pores. Monolithic columns with accessible porous structures can be beneficial for size-based separations of ultrahigh molar mass analytes with low diffusion coefficients.

Characterization of hybrid organo-silica monoliths for possible application in the gradient elution of peptides

We characterized thermally polymerized organo-silica hybrid monolithic capillaries to test their applicability in the gradient elution of peptides. We have used a single-pot approach utilizing 3-(methacryloyloxy)propyltrimethoxysilane (MPTMS), ethylene dimethacrylate (EDMA), and n-octadecyl methacrylate (ODM) as functional monomers. The organo-silica monolith containing MPTMS and EDMA was compared with the stationary phase prepared by adding ODM to the original polymerization mixture. Column prepared using a three-monomer system provided a lower accessible volume of flow-through pores, a higher proportion of mesopores, and higher efficiency. We utilized isocratic and gradient elution data to predict peak widths in gradient elution. Both protocols provided comparable results and can be used for peptide peak width prediction. However, applying gradient elution data for peak width prediction seems simpler. Finally, we tested the effect of gradient time on achievable peak capacity in the gradient elution of peptides with a column prepared with a three-monomer system providing a higher peak capacity. However, the performance of hybrid organo-silica monolithic stationary phases in gradient elution of peptides must be improved compared to other monolithic stationary phases. The limiting factor is column efficiency in highly aqueous mobile phases, which needs to be focused on.

Liquid chromatography at the university of pardubice: a tribute to Professor Pavel Jandera

Pavel Jandera was a world-leading analytical chemist who devoted his entire professional life to research in the field of high-performance liquid chromatography. During all his scientific career, he worked at the Department of Analytical Chemistry at the University of Pardubice, Czech Republic. His greatest contribution to the field of liquid chromatography was the introduction of a comprehensive theory of liquid chromatography with programmed elution conditions. He was also involved in the research of gradient elution techniques in preparative chromatography, modeling of retention and selectivity in various phase systems, preparation of organic monolithic microcolumns and, last but not least, in the development of theory and practical applications of two-dimensional liquid chromatography, mainly in the comprehensive form. In this review article, we have tried to capture the highlights of his scientific career and provide the readers with a detailed overview of Pavel Jandera's contribution to the evolution of separation sciences. This article is protected by copyright. All rights reserved.

Polymeric stationary phases for size exclusion chromatography: A review

Synthetic and natural macromolecules are commonly used in a variety of fields such as plastics, nanomedicine, biotherapeutics, drug delivery and tissue engineering. Characterising macromolecules in terms of their structural parameters (size, molar mass and distribution, architecture) is key to have a better understanding of their structure-property relationships. Size exclusion chromatography (SEC) is a commonly used technique for polymer characterization since it offers access to the determination of the size of a macromolecule, its molar mass and the molar mass distribution. Moreover, detectors that allow the determination of true molar masses, macromolecule's architecture and the composition of copolymers can be coupled to the chromatographic system. Like other chromatographic techniques, the stationary phase is of paramount importance for efficient SEC separations. This review presents the basic principles for the design of stationary phases for SEC as well as synthetic methods currently used in the field. Current status of fully-porous polymeric stationary phases used in SEC is reviewed and their advantages and limitations are also discussed. Finally, the potential of polymer monoliths in SEC is also covered, highlighting the limitations this column technology could address. However, further development in the polymer structure is needed to consider this column technology in the field of macromolecule separation.

Advances in organic polymer-based monolithic column technology for high-resolution liquid chromatography-mass spectrometry profiling of antibodies, intact proteins, oligonucleotides, and peptides

This review focuses on the preparation of organic polymer-based monolithic stationary phases and their application in the separation of biomolecules, including antibodies, intact proteins and protein isoforms, oligonucleotides, and protein digests. Column and material properties, and the optimization of the macropore structure towards kinetic performance are also discussed. State-of-the-art liquid chromatography-mass spectrometry biomolecule separations are reviewed and practical aspects such as ion-pairing agent selection and carryover are presented. Finally, advances in comprehensive two-dimensional LC separations using monolithic columns, in particular ion-exchange×reversed-phase and reversed-phase×reversed-phase LC separations conducted at high and low pH, are shown.

Cross-linker effects on the separation efficiency on (poly)methacrylate capillary monolithic columns. Part I. Reversed-phase liquid chromatography

We synthesized 8 polymethacrylate monolithic capillary columns using laurylmethacrylate functional monomer and various cross-linking monomers differing in the polarity and size. The efficiency of monolithic columns for low-molecular compounds significantly improved with increasing number of repeat non-polar methylene groups in the cross-linker molecules, correlating with greater proportion of small pores with size less than 50 nm. The best efficiency with HETP=25 μm for alkylbenzenes was achieved for columns prepared using hexamethylene dimethacrylate (HEDMA). Columns prepared with polar (poly)oxyethylene dimethacrylate cross-linkers show also improved efficiency with increasing chain length and generally better performance in comparison to the (poly)methylene dimethacrylate cross-linkers of comparable size, however with less apparent effects of the chain lengths on the pore distribution. The monolithic columns prepared with tetraoxyethylene dimethacrylate (TeEDMA) showed the best efficiency of all the columns tested, corresponding to HETP=15 μm (approx. 70,000 theoretical plates/m), show excellent column-to-column reproducibility with standard deviations of 2.5% in retention times, good permeability and low mass transfer resistance, so that is suitable for fast separation of low-molecular compounds in 2 min or less. By modification of the fused-silica capillary inner walls pre-treatment procedure, very good long-term stability was achieved even in 0.5 mm i.d. capillary format. The TeEDMA column can be also used for size-exclusion chromatography of lower non-polar synthetic polymers, whereas it is less suitable for separations of proteins than the HEDMA column.

Recent advances in the design of organic polymer monoliths for reversed-phase and hydrophilic interaction chromatography separations of small molecules

Owing to their favorable porous structure with pore size distribution shifted towards large flow-through pores, organic polymer monoliths have been mainly employed for the separation of macromolecules in gradient elution liquid chromatography. The absence of significant amounts of small pores with a stagnant mobile phase and the resulting low surface area were considered as the main reason for their poor behavior in the isocratic separation of small molecules. Several recent efforts have improved the separation power of organic polymer monoliths for small molecules offering column efficiency up to tens of thousands of plates per meter. These attempts include optimization of the composition of polymerization mixture, including the variation of functional monomer, the cross-linking monomer, and the porogen solvents mixture, adjustment of polymerization temperature, and time. Additionally, post-polymerization modifications including hypercross-linking and the use of carbon nanostructures showed significant improvement in the column properties. This review describes recent developments in the preparation of organic polymer monoliths suitable for the separation of small molecules in the isocratic mode as well as the main factors affecting the column efficiency.

Preparation of methacrylate-based anion-exchange monolithic microbore column for chromatographic separation of DNA fragments and oligonucleotides

In this paper, we report on the preparation of a microbore-scale (1 mm i.d.) anion-exchange monolithic column suitable not only for analytical purposes but also for potentially preparative applications. In order to meet the conflicting requirements of high permeability and good mechanical strength, the following two-step procedure was applied. First, an epoxy-containing monolith was synthesized by in situ copolymerization of glycidyl methacrylate (GMA) and ethylene dimethacrylate (EDMA) within the confines of a silicosteel tubing of 1.02 mm i.d. and 1/16" o.d. in the presence of a ternary porogenic mixture of 1-propanol, 1,4-butanediol, and water. The monolithic matrix was subsequently converted into weak anion-exchanger via the ring-opening reaction of epoxy group with diethyl amine. The dynamic binding capacity was 21.4 mg mL(-1) for bovine serum albumin (BSA) at 10% breakthrough. The morphology and porous structure of this monolith were assessed by scanning electron microscope (SEM) and inverse size exclusion chromatography (ISEC). To optimize the separation efficiency, the effects of various chromatographic parameters upon the separation of DNA fragments were investigated. The resulting monolithic anion exchanger demonstrated good potential for the separation of both single- and double-stranded DNA molecules using a gradient elution with NaCl in Tris-HCl buffer (20 mM). Oligodeoxythymidylic acids (dT(12)-dT(18)) were successfully resolved at pH 8, while the fragments of 20 bp DNA ladder, 100 bp DNA ladder, and pBR322-HaeIII digest were efficiently separated at pH 9.

New monolithic capillary columns with well-defined macropores based on poly(styrene-co-divinylbenzene)

Macroporous polymer monoliths based on poly(styrene-co-divinylbenzene) with varied styrene/divinylbenzene ratios have been prepared by organotellurium-mediated living radical polymerization. The well-defined cocontinuous macroporous structure can be obtained by polymerization-induced spinodal decomposition, and the pore structures are controlled by adjusting the starting composition. The separation efficiency of small molecules (alkylbenzenes) in the obtained monoliths has been evaluated in the capillary format by high-performance liquid chromatography (HPLC) under the isocratic reversed-phase mode. Baseline separations of these molecules with a low pressure drop (∼2 MPa) have been achieved because of the well-defined macropores and to the less-heterogeneous cross-linked networks.

Hypercrosslinking: new approach to porous polymer monolithic capillary columns with large surface area for the highly efficient separation of small molecules

Monolithic polymers with an unprecedented surface area of over 600 m(2)/g have been prepared from a poly(styrene-co-vinylbenzyl chloride-co-divinylbenzene) precursor monolith that was swollen in 1,2-dichloroethane and hypercrosslinked via Friedel-Crafts reaction catalyzed by ferric chloride. Both the composition of the reaction mixture used for the preparation of the precursor monolith and the conditions of the hypercrosslinking reaction have been varied using mathematical design of experiments and the optimized system validated. Hypercrosslinked monolithic capillary columns contain an array of small pores that make the column ideally suited for the high efficiency isocratic separations of small molecules such as uracil and alkylbenzenes with column efficiencies reproducibly exceeding 80,000 plates/m for retained compounds. The separation process could be accelerated while also improving peak shape through the use of higher temperatures and a ternary mobile phase consisting of acetonitrile, tetrahydrofuran, and water. As a result, seven compounds were well separated in less than 2 min. These columns also facilitate separations of peptide mixtures such as a tryptic digest of cytochrome c using a gradient elution mode which affords a sequence coverage of 93%. A 65 cm long hypercrosslinked capillary column used in size exclusion mode with tetrahydrofuran as the mobile phase afforded almost baseline separation of toluene and five polystyrene standards.