Surface-alkylated polystyrene monolithic columns for peptide analysis in capillary liquid chromatography-electrospray ionization mass spectrometry

Trends in monoliths: Packings, stationary phases and nanoparticles

Monoliths media are gaining interest as excellent substitutes to conventional particle-packed columns. Monolithic columns show higher permeability and lower flow resistance than conventional liquid chromatography columns, providing high-throughput performance, resolution and separation in short run times. Monolithic columns with longer length, smaller inner diameter and specific selectivity to peptides or enantiomers have been played important role in hyphenated system. Monolithic stationary phases possess great efficiency, resolution, selectivity and sensitivity in the separation of complex biological samples, such as the complex mixtures of peptides for proteome analysis. The development of monolithic stationary phases has opened the new avenue in chromatographic separation science and is in turn playing much more important roles in the wide application area. Monolithic stationary phases have been widely used in fast and high efficiency one- and multi-dimensional separation systems, miniaturized devices, and hyphenated system coupled with mass spectrometers. The developing technology for preparation of monolithic stationary phases is revolutionizing the column technology for the separation of complex biological samples. These techniques using porous monoliths offer several advantages, including miniaturization and on-line coupling with analytical instruments. Additionally, monoliths are ideal support media for imprinting template-specific sites, resulting in the so-called molecularly-imprinted monoliths, with ultra-high selectivity. In this review, the origin of the concept, the differences between their characteristics and those of traditional packings, their advantages and drawbacks, theory of separations, the methods for the monoliths preparation of different forms, nanoparticle monoliths and metal-organic framework are discussed. Two application areas of monolithic metal-organic framework and nanoparticle monoliths are provided. The review article discusses the results reported in a total of 218 references. Other older references were included to illustrate the historical development of monoliths, both in preparation and types, as well as separation mechanism.

One-Pot Fabrication of Hierarchically Bicontinuous Polystyrene Monoliths with Homogeneous Skeletons and Glycopolymer Surfaces

The hierarchically bicontinuous polystyrene monoliths (HBPMs) with homogeneous skeletons and glycopolymer surfaces are fabricated for the first time based on the medium internal phase emulsion (MIPE) templating method via activator generated by electron transfer for atom transfer radical polymerization (AGET ATRP). The synergistic self-assembly of amphiphilic diblock glycopolymer (ADG) and Pluronic F127 (PF127) at the oil/water interface via hydrogen bonding interaction contributes to the formation of bicontinuous MIPE with deformed neighboring water droplets, resulting in the highly interconnected HBPM after polymerization. There is a bimodal pore size distribution in the HBPM, that is, through pores (150-5000 nm) and mesopores (10-150 nm). The HBPMs as prepared show excellent biocompatibility, homogeneous skeletons, strong mechanical strength, and high bed permeability, overcoming the practical limitations of the second generation of polystyrene (PS) monoliths. Glycoprotein concanavalin A (Con A) can be easily and quickly separated by the HBPM in hydrophilic interaction chromatography (HILIC) mode. These results suggest the HBPMs have great potentials in catalysis, separations, and biomedical applications.

Monolith columns for liquid chromatographic separations of intact proteins: A review of recent advances and applications

In this article we survey 256 references (with an emphasis on the papers published in the past decade) on monolithic columns for intact protein separation. Protein enrichment and purification are included in the broadly defined separation. After a brief introduction, we describe the types of monolithic columns and modes of chromatographic separations employed for protein separations. While the majority of the work is still in the research and development phase, papers have been published toward utilizing monolithic columns for practical applications. We survey these papers as well in this review. Characteristics of selected methods along with their pros and cons will also be discussed.

Abnormal adsorption and desorption behavior of pharmaceutical drugs on polystyrene microspheres

We report an abnormal adsorption and desorption behavior where a stronger adsorption interaction between polystyrene particles and pharmaceutical drugs results in preferable desorption behavior.

Monoliths in capillary electrochromatography and capillary liquid chromatography in conjunction with mass spectrometry

Here, we have reviewed separation studies utilizing monolithic capillary columns for separation of compounds preceding MS analysis. The review is divided in two parts according to the used separation method, namely CEC and capillary LC (cLC). Based on our overview, monolithic CEC-MS technique have been more focused on the syntheses of highly specialized and selective separation phase materials for fast and efficient separation of specific types of analytes. In contrast, monolithic cLC-MS is more widely used and is often employed, for instance, in the analysis of oligonucleotides, metabolites, and peptides and proteins in proteomic studies. While poly(styrene-divinylbenzene)-based and silica-based monolithic capillaries found their place in proteomic analyses, the other laboratory-synthesized monoliths still wait for their wider utilization in routine analyses. The development of new monolithic materials will most likely continue due to the demand of more efficient and rapid separation of increasingly complex samples.

Coating gigaporous polystyrene microspheres with cross-linked poly(vinyl alcohol) hydrogel as a rapid protein chromatography matrix

Gigaporous polystyrene (PS) microspheres were hydrophilized by in situ polymerization to give a stable cross-linked poly(vinyl alcohol) (PVA) hydrogel coating, which can shield proteins from the hydrophobic PS surface underneath. The amination of microspheres (PS-NH2) was first carried out through acetylization, oximation and reduction, and then 4,4'-azobis (4-cyanovaleric acid) (ACV), a polymerization initiator, was covalently immobilized on PS-NH2 through amide bond formation, and the cross-linked poly(vinyl acetate) (PVAc) was prepared by radical polymerization at the surfaces of ACV-immobilized PS microspheres (PS-ACV). Finally, the cross-linked PVA hydrogel coated gigaporous PS microspheres (PS-PVA) was easily achieved through alcoholysis of PVAc. Results suggested that the PS microspheres were effectively coated with cross-linked PVA hydrogel, where the gigaporrous structure remained under optimal conditions. After hydrophilic modification (PS-PVA), the protein-resistant ability of microspheres was greatly improved. The hydroxyl-rich PS-PVA surface can be easily derivatized by classical chemical methods. Performance advantages of the PS-PVA column in flow experiment include good permeability, low backpressure, and mechanical stability. These results indicated that PS-PVA should be promising in rapid protein chromatography.

Simultaneous extraction and separation of flavonols and flavones from Chamaecyparis obtusa by multi-phase extraction using an ionic liquid-modified microsphere polymer

INTRODUCTION

Flavonols and flavones, especially quercitrin, myricetin and amentoflavone, are the main anti-bacterial and anti-cancer compounds in Chamaecyparis obtuse. Multi-phase extraction is a new method that can extract and separate target compounds simultaneously.

OBJECTIVE

An amino ionic liquid immobilised microsphere polymer was used as a multi-phase extraction sorbent to extract and separate quercitrin, myricetin and amentoflavone from Chamaecyparis obtusa.

METHODOLOGY

The sorbent and Chamaecyparis obtusa powder were packed into a single cartridge. Using a fixed volume of methanol with five repetitions, the target compounds were extracted from the powder to the sorbent. The sorbent was then washed with n-hexane to remove any interfering species and the target compounds were eluted sequentially using water, methanol and methanol containing 1% acetic acid (vol.).

RESULTS

Under the optimised conditions, 0.45 mg/g of quercitrin, 0.18 mg/g of myricetin and 0.12 mg/g of amentoflavone from 2.0 g of powder were obtained by multi-phase extraction using 0.3 g of sorbent.

CONCLUSION

The method described has a low deviation error, requires a small amount of solvent and is highly selective and reproducible.

CEC: selected developments that caught my eye since the year 2000

During the last decade, a number of new developments have emerged in the field of CEC. This paper focuses only on monolithic columns prepared from synthetic polymers. Monolithic columns have become a well-established format of stationary phases for CEC immediately after their inception in the mid-1990s. They are readily prepared in situ from liquid precursors. Also, the control over both porous properties and surface chemistries is easy to achieve. These advantages make the monolithic separation media an attractive alternative to capillary columns packed with particulate materials. Since the number of papers concerned with just this single topic of polymer-based monolithic CEC columns is large, this overview describes only those approaches this author found interesting.

Application of micro- and nano-HPLC to the determination and characterization of bioactive and biomarker peptides

This article reviews the works published since 2001 (included) on the micro/nano-HPLC analysis of bioactive and biomarker peptides. The main achievements related to the improvement of the detection sensitivity, quantitation repeatability and reproducibility, and separation selectivity are highlighted. A wide attention is paid to the application of micro/nano-HPLC to the analysis of bioactive peptides in biological matrices. The uses of micro/nano-HPLC in peptidomics to discover new endogenous bioactive peptides and to develop quantitation procedures to compare the levels of peptides of interest in two different biological samples are also considered. Finally, the application of micro/nano-HPLC to the analysis of biomarker peptides for various diseases is also included in this review.

Development of capillary electrochromatography with poly(styrene-divinylbenzene-vinylbenzenesulfonic acid) monolith as the stationary phase

A new polystyrene-based monolithic stationary phase, which was prepared by single step in situ copolymerization of styrene, divinylbenzene and vinylbenzenesulfonic acid (VBSA), was developed as a separation column for capillary electrochromatography, in which VBSA was employed as the charge-bearing monomer. Polymerization time of the polystyrene-based monolith had slightly influenced the separation time of the tested analytes, but it effectively altered their separation resolutions. Furthermore, baseline separation for a wider range of acetonitrile levels of mobile phase was achieved when a monolithic column prepared by a longer polymerization time was used. This novel polystyrene-based monolithic column provided an adequate electroosmotic flow either in basic or acidic mobile phase when VBSA level was maintained at 2.6% (w/w). Finally, this proposed polystyrene-based column allowed seven tested analytes to achieve a reproducible baseline separation within 2.2 min with theoretical plate numbers higher than 164 000 plates/m.

Novel monolithic poly(p-methylstyrene-co-bis(p-vinylbenzyl)dimethylsilane) capillary columns for biopolymer separation

Hydrophobic organo-silane based monolithic capillary columns were prepared by thermally initiated free radical polymerisation within the confines of 200 microm i.d. fused silica capillaries. A novel crosslinker, namely bis(p-vinylbenzyl)dimethylsilane (BVBDMS), was copolymerised with p-methylstyrene (MS) in the presence of 2-propanol and toluene, using alpha,alpha'-azoisobutyronitrile (AIBN) as initiator. Monolithic capillary columns, differing in the total monomer, microporogen content and microporogen nature were fabricated and the chromatographic efficiency of each monolith, regarding the separation of proteins, peptides and oligonucleotides, was evaluated and compared. Changes in monolith morphology were monitored by scanning electron microscopy (SEM). Porosity and specific surface areas of the supports were studied by means of mercury intrusion porosimetry and BET measurements, respectively. Pressure drop vs. flow rate measurements proved the prepared poly(p-methylstyrene-co-bis(p-vinylbenzyl)dimethylsilane) (MS/BVBDMS) monoliths to be mechanically stable and swelling propensity (SP) factors of 0.78-1.10 indicate high crosslinking homogeneity.

Fabrication of a poly(styrene-octadecene-divinylbenzene) monolithic column and its comparison with a poly(styrene-divinylbenzene) monolithic column for the separation of proteins

In this paper, a poly(styrene-octadecene-divinylbenzene) (PS-OD-DVB) monolithic column was prepared in one step by introducing a C18 carbon chain as monomer. N,N-Dimethylformamide and decanol served as porogens to make a homogeneous polymerization mixture in a fused silica capillary (320 microm inner diameter). Its physical and chromatographic properties were compared with those of poly(styrene-divinylbenzene) (PS-DVB) monolithic column, which was also fabricated by in-situ polymerization in a fused silica capillary with the same inner diameter. Six standard proteins were used to evaluate the columns and their potential application for the separation of human hemoglobin was also discussed. It was shown that the PS-OD-DVB and PS-DVB monoliths appeared to have similar efficiency for rapid separation of six proteins within 3.5 min. The PS-OD-DVB monolith was found to have higher loading capacity and higher resolution for the separation of alpha and beta chains of hemoglobin because of the introduction of C18 carbon chains, and shows great potential for the separation of bio-macromolecules.

Novel monolithic poly(phenyl acrylate-co-1,4-phenylene diacrylate) capillary columns for biopolymer chromatography

Monolithic capillary columns were prepared by thermally initiated free radical polymerisation of phenyl acrylate (PA) and 1,4-phenylene diacrylate (PDA) in the confines of 200 microm I.D. fused silica capillaries. Polymerisation was performed in the presence of 2-propanol and tetrahydrofuran (THF) as inert diluents (porogens), using alpha,alpha'-azoisobutyronitrile (AIBN) as initiator. Morphology and porosity of the resulting monoliths were comprehensively studied by scanning electron microscopy (SEM), mercury intrusion porosimetry and inverse size-exclusion chromatography (ISEC). The novel poly(phenyl acrylate-co-1,4-phenylene diacrylate) (PA/PDA) monoliths showed high mechanical stability and were successfully applied to the separation of proteins and oligodeoxynucleotides, employing reversed-phase (RP) and ion-pair reversed-phase (IP-RP) conditions, respectively. Maximum loading capacities for cytochrome c and d(pT)(16) were evaluated and found to be in the region of 200 fmol. Batch-to-batch reproducibility was determined for three independently prepared PA/PDA monolithic capillary columns. Relative standard deviations (RSDs) of retention time (t(R)) of 0.7-1.6% for proteins and 0.2-2.5% for d(pT)(12-18) proved high reproducibility of the PA/PDA supports.

Use of monolithic supports in proteomics technology

An overview on the utilization of monoliths in proteomics technology will be given. Both silica- and polymer-based monoliths have broad use for microseparation of tryptic peptides in reversed-phase (RP) mode before identification by mass spectrometry (MS) or by MS/MS. For two-dimensional (2D) LC separation of peptides before MS or MS/MS analysis, a combination of ion-exchange, usually cation-exchange (CEX) chromatography with RP chromatography on monolithic supports can be employed. Immobilized metal ion affinity chromatography monoliths with immobilized Fe3+-ions are used for the isolation of phosphopeptides. Monoliths with immobilized affinity ligands are usually applied to the rapid separation of proteins and peptides. Miniaturized reactors with immobilized proteolytic enzymes are utilized for rapid on- or offline digestion of isolated proteins or protein mixtures prior to identification by LC-MS/MS. Monoliths also have broad potential for application in sample preparation, prior to further proteomic analyses. Monolithic supports with large pore sizes can be exploited for the isolation of nanoparticles, such as cells, organelles, viruses and protein aggregates. The potential for further adoption of monolithic supports in protein separation and enrichment of low abundance proteins prior to proteolytic digestion and final LC-MS/MS protein identification will be discussed.

Stability and repeatability of capillary columns based on porous monoliths of poly(butyl methacrylate-co-ethylene dimethacrylate)

Monolithic poly(butyl methacrylate-co-ethylene dimethacrylate) capillary columns have been prepared via either thermally or photochemically initiated polymerization of the corresponding monomers and the repeatability of their preparation has been explored. Three separate batches of 5 columns each were prepared using thermal and photochemical initiation for a total of 30 columns. All 30 capillary columns were tested in liquid chromatography-electrospray ionisation mass spectrometry mode for the separation of a model mixture of three proteins--ribonuclease A, cytochrome c and myoglobin. Excellent repeatability of retention times was observed for the proteins as evidenced by relative standard deviation (RSD) values of less than 1.5%. Somewhat broader variations with RSD values of up to 10% were observed for the pressure drop in the columns. The stability of retention times was also monitored using a single monolithic column and no significant shifts in either retention times or back pressure was observed in a series of almost 2200 consecutive protein separations.

CEC with monolithic poly(styrene-divinylbenzene-vinylsulfonic acid) as the stationary phase

In this study, poly(styrene-divinylbenzene-vinylsulfonic acid) monolithic columns, prepared by singlestep in situ polymerization, were first used as separation columns for CEC in which vinylsulfonic acid was employed as the charge-bearing monomer. The effects of the polymerization conditions (compositions of monomer and porogenic solvent, and polymerization time) on the chromatographic property of the polystyrene-based monolithic column were examined. Furthermore, an increase in water content of the porogenic solvent markedly altered the retention behaviors of these analytes, where the monolithic column was able to be produced in a higher ratio of vinylsulfonic acid. Finally, the study demonstrated that acidic analytes could be successfully separated by the polystyrene-based monolithic column under an acidic mobile phase.

Capillary scale monolithic trap column for desalting and preconcentration of peptides and proteins in one- and two-dimensional separations

Monolithic columns based on poly-(styrene-divinylbenzene) (PS-DVB) were utilized both for preconcentration (in 10 mm x 0.20 mm I.D. format) and analytical separation (in 60 mm x 0.20 and 0.10 mm I.D. format) of peptides and proteins in column switching micro-scale high-performance liquid chromatography. A special holder for short monolithic preconcentration columns was designed and pressure durability tests approved long-term stability up to 400 bar. An 11-20% decrease in the average peak widths of nine peptides was obtained upon combining a preconcentration column with an analytical column as compared with a setup using an analytical column only. Trapping efficiency, especially for small and hydrophilic peptides, was optimized by using 0.10% heptafluorobutyric acid instead of 0.050% trifluoroacetic acid as solvent additive during sample loading. Using a 10 mm x 0.20 mm I.D. preconcentration column, loadabilities between 0.5 and 1.6 microg were determined by frontal analysis of proteins and bioactive peptides, respectively. A 100-fold concentration followed by direct on-line intact mass determination is demonstrated for diluted (3 micromolL(-1)) protein solutions. The applicability of the monolithic preconcentration column for multidimensional chromatography was tested by off-line two-dimensional separation, combining strong cation-exchange chromatography and ion-pair reversed-phase chromatography. Peptide identification data from digested protein mixtures demonstrated reproducibilities of 46-75% in triplicate analyses, and confident peptide identifications of low abundant peptides even in the presence of a 650-fold molar excess of high abundant peptides.

Monolithic media in microfluidic devices for proteomics

Considerable effort has been invested in the development of integrated microfluidic devices for fast and highly efficient proteomic studies. Among various fabrication techniques for the preparation of analytical components (separation columns, reactors, extractors, valves, etc.) in integrated microchips, in situ fabrication of monolithic media is receiving increasing attention. This is mainly due to the ease and simplicity of preparation of monolithic media and the availability of various precursors and chemistries. In addition, UV-initiated photopolymerization technique enables the incorporation of multiple analytical components into specified parts of a single microchip using photomasks. This review summarizes preparation methods for monolithic media and their application as microfluidic analytical components in microchips.

Separation of parabens in capillary electrochromatography using poly(styrene-divinylbenzene-methacrylic acid) monolithic column

In this study, a series of poly(styrene-divinylbenzene-methacrylic acid) monolithic capillaries was used as the separation column of CEC for the analyses of parabens in commercial pharmaceutical and cosmetic products. The results showed that the chromatographic characteristics of these analytes were strongly affected by the preparation condition of the monolithic column including monomer content, porogenic solvent composition, and polymerization time. Baseline separations were markedly sped up by lowering the polymerization time without any obvious loss of resolution. Furthermore, mobile-phase composition (pH, ACN, and electrolyte concentration) was also able to effectively improve the separation behavior. Similar to the influence of lowering the polymerization time, retention times for all analytes were significantly shortened in the CEC method by decreasing the electrolyte concentration in the mobile phase.

Octadecylated Silica Monolith Capillary Column with Integrated Nanoelectrospray Ionization Emitter for Highly Efficient Proteome Analysis

An improved strategy for the preparation of octadecylated silica monolith capillary column with high homogeneity was proposed. Column performance was evaluated by nanoscale HPLC. The design for constructing an integrated nanoelectrospray emitter on the octadecylated silica monolith capillary column was first introduced. In comparison with the separated configuration where the emitter is connected to monolithic capillary column by the aid of a zero dead volume union, the integrated capillary column has the inherent advantage of the minimized extracolumn volume thus providing improved separation quality. The performance of the integrated monolithic capillary column was evaluated by separation of BSA tryptic digest, and peak capacity of 313 with a 30-cm column was obtained. The high separation performance allowed highly confident identification of 662 distinct proteins through assignment of 1933 unique peptides by analysis of tryptic digest of 0.5 mug of Saccharomyces cerevisiae proteins. The higher separation efficiency by a 60-cm monolithic capillary column increased the proteome coverage with identification of 1323 proteins through assignment of 5501 unique peptides over 400-min gradient elution.

Ultra-fast tandem mass spectrometry scanning combined with monolithic column liquid chromatography increases throughput in proteomic analysis

Liquid chromatography combined with electrospray ionization mass spectrometry (LC/ESI-MS) has been used successfully for the characterization of biomolecules in proteomics in the last few years. This methodology relied largely on the use of reversed-phase chromatography, in particular C18-based resins, which are suitable for separation of peptides. Here we show that polymeric [polystyrene divinylbenzene] monolithic columns can be used to separate peptide mixtures faster and at a higher resolution. For 500 fmol bovine serum albumin, up to 68% sequence coverage and Mascot Mowse scores of >2000 were obtained using a 9 min gradient on a monolithic column coupled to an ion trap mass spectrometer with ultra-fast MS/MS scan rates. In order to achieve similar results using C18 columns, it was necessary to extend gradient times to 30 min. In addition, we demonstrate the utility of this approach for the analysis of whole Escherichia coli cell lysates by one-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (1D-SDS-PAGE) in combination with LC/MS/MS using 4 min gradients on monolithic columns. Our results indicate higher throughput capabilities of monolithic columns (3-fold gain in time or more) for conventional proteomics applications, such as protein identification and high sequence coverage usually required for detection of post-translational modifications (PTMs). Further optimization of sensitivity and quality of sequence information is discussed, in particular when combined with mass spectrometers that have very fast MS-MS/MS switching and scanning capabilities.

Towards high capacity latex-coated porous polymer monoliths as ion-exchange stationary phases

The preparation of high capacity agglomerated monolithic ion-exchangers for capillary ion chromatography is described. Post-modification of reactive monoliths was investigated as an alternative to co-polymerisation of a suitable functional monomer with an overarching goal of increasing ion-exchange capacity. Direct sulfonation of poly styrene-co-divinyl benzene monoliths using concentrated sulfuric acid or chlorosulfonic acid was unsuccessful even for monoliths containing as low as 8% crosslinker. In contrast, chemical transformation of reactive monoliths containing glycidyl methacrylate was used to increase the ion-exchange capacity by up to more than thirty-fold with ion exchange capacities of 14-29 microequiv g(-1) achieved. Three different reactions were considered, including reaction with 4-hydroxybenenesulfonic acid under basic conditions; reaction with thiobenzoic acid followed by transformation to a reactive thiol and the subsequent oxidation to the sulfonic acid; and direct sulfonation with sodium sulfite. Of these, the reaction with sodium sulfite resulted in the most significant increase in the capacity and the best separation performance. In the isocratic mode separation efficiencies of over 13,500 plates m(-1) were observed (for iodate). The separation of seven inorganic anions was also demonstrated using a hydroxide gradient.