A study of surface modification and anchoring techniques used in the preparation of monolithic microcolumns in fused silica capillaries

A protocol for fabrication of polymer monolithic capillary columns and tuning the morphology targeting high-resolution bioanalysis in gradient-elution liquid chromatography

Polymer monolithic stationary phases are designed as a continuous interconnected globular material perfused by macropores. Like packed column, where separation efficiency is related to particle diameter, the efficiency of monoliths can be enhanced by tuning the size of both the microglobules and macropores. This protocol described the synthesis of poly(styrene-co-divinylbenzene) monolithic stationary phases in capillary column formats. Moreover, guidelines are provided to tune the macropore structure targeting high-throughput and high-resolution monolith chromatography. The versatility of these columns is exemplified by their ability to separate tryptic digests, intact proteins, and oligonucleotides under a variety of chromatographic conditions. The repeatability of the presented column fabrication process is demonstrated by the successful creation of 12 columns in three different column batches, as evidenced by the consistency of retention times (coefficients of variance [c.v.] = 0.9%), peak widths (c.v. = 4.7%), and column pressures (c.v. = 3.1%) across the batches.

UV polymerization fabrication method for polymer composite based optical fiber sensors

Optical fiber (OF) sensors are critical optical devices with excellent sensing capabilities and the capacity to operate in remote and hostile environments. However, integrating functional materials and micro/nanostructures into the optical fiber systems for specific sensing applications has limitations of compatibility, readiness, poor control, robustness, and cost-effectiveness. Herein, we have demonstrated the fabrication and integration of stimuli-responsive optical fiber probe sensors using a novel, low-cost, and facile 3D printing process. Thermal stimulus-response of thermochromic pigment micro-powders was integrated with optical fibers by incorporating them into ultraviolet-sensitive transparent polymer resins and then printed via a single droplet 3D printing process. Hence, the thermally active polymer composite fibers were grown (additively manufactured) on top of the commercial optical fiber tips. Then, the thermal response was studied within the temperature range of (25-35 °C) and (25-31 °C) for unicolor and dual color pigment powders-based fiber-tip sensors, respectively. The unicolor (with color to colorless transition) and dual color (with color to color transition) powders-based sensors exhibited substantial variations in transmission and reflection spectra by reversibly increasing and decreasing temperatures. The sensitivities were calculated from the transmission spectra where average change in transmission spectra was recorded as 3.5% with every 1 °C for blue, 3% for red and 1% for orange-yellow thermochromic powders based optical fiber tip sensors. Our fabricated sensors are cost-effective, reusable, and flexible in terms of materials and process parameters. Thus, the fabrication process can potentially develop transparent and tunable thermochromic sensors for remote sensing with a much simpler manufacturing process compared to conventional and other 3D printing processes for optical fiber sensors. Moreover, this process can integrate micro/nanostructures as patterns on the optical fiber tips to increase sensitivity. The developed sensors may be employed as remote temperature sensors in biomedical and healthcare applications.

Terminally Phosphorylated Triblock Polyethers Acting Both as Templates and Pore-Forming Agents for Surface Molecular Imprinting of Monoliths Targeting Phosphopeptides

The novel process reported here described the manufacture of monolithic molecularly imprinted polymers (MIPs) using a terminally functionalized block copolymer as the imprinting template and pore-forming agent. The MIPs were prepared through a step-growth polymerization process using a melamine-formaldehyde precondensate in a biphasic solvent system. Despite having a relatively low imprinting factor, the use of MIP monolith in liquid chromatography demonstrated the ability to selectively target desired analytes. An MIP capillary column was able to separate monophosphorylated peptides from a tryptic digest of bovine serum albumin. Multivariate data analysis and modeling of the phosphorylated and nonphosphorylated peptide retention times revealed that the number of phosphorylations was the strongest retention contributor for peptide retention on the monolithic MIP capillary column.

In-Capillary Photodeposition of Glyphosate-Containing Polyacrylamide Nanometer-Thick Films

The present research reports on in-water, site-specific photodeposition of glyphosate (GLP)-containing polyacrylamide (PAA-GLP) nanometer-thick films (nanofilms) on an inner surface of fused silica (fused quartz) microcapillaries presilanized with trimethoxy(octen-7-yl)silane (TMOS). TMOS was chosen because of the vinyl group presence in its structure, enabling its participation in the (UV light)-activated free-radical polymerization (UV-FRP) after its immobilization on a fused silica surface. The photodeposition was conducted in an aqueous (H₂O/ACN; 3:1, v/v) solution, using UV-FRP (λ = 365 nm) of the acrylamide (AA) functional monomer, the N,N'-methylenebis(acrylamide) (BAA) cross-linking monomer, GLP, and the azobisisobutyronitrile (AIBN) UV-FRP initiator. Acetonitrile (ACN) was used as the porogen and the solvent to dissolve monomers and GLP. Because of the micrometric diameters of microcapillaries, the silanization and photodeposition procedures were first optimized on fused silica slides. The introduction of TMOS, as well as the formation of PAA and PAA-GLP nanofilms, was determined using atomic force microscopy (AFM), scanning electron microscopy with energy-dispersive X-ray (SEM-EDX) spectroscopy, and confocal micro-Raman spectroscopy. Particularly, AFM and SEM-EDX measurements determined nanofilms' thickness and GLP content, respectively, whereas in-depth confocal (micro-Raman spectroscopy)-assisted imaging of PAA- and PAA-GLP-coated microcapillary inner surfaces confirmed the successful photodeposition. Moreover, we examined the GLP impact on polymer gelation by monitoring hydration in a hydrogel and a dried powder PAA-GLP. Our study demonstrated the usefulness of the in-capillary micro-Raman spectroscopy imaging and in-depth profiling of GLP-encapsulated PAA nanofilms. In the future, our simple and inexpensive procedure will enable the fabrication of polymer-based microfluidic chemosensors or adsorptive-separating devices for GLP detection, determination, and degradation.

ACE2 and SARS-CoV-2-Main Protease Capillary Columns for Affinity Chromatography: Testimony of the Binding of Dexamethasone and its Carbon Nanotube Nanovector

In this paper, each of the two following proteins, the angiotensin-converting enzyme 2 (ACE2) and the Main protease (Main pro) of the Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) were grafted for the first time on homemade neutravidin poly(GMA-co-EDMA) capillary columns for the research of their ligands. The effect of the column diameter on the quantity of immobilized biotinylated protein was studied. For a capillary length of 40 mm, when its internal diameter varied from 75 to 25 μm, the grafted quantity of ACE2 decreased by 85% (from 1.50 to 0.24 μg). Among all the studied ligands, a particular vigilance has been given for dexamethasone, a widely used molecule today for adult patients hospitalized with SARS-CoV-2. Competition experiments were performed with SARS-CoV-2 Receptor Binding Domain used as reference molecule with the ACE2 affinity column to assess the orthosteric binding site of dexamethasone (Dex) on ACE2. This ligand was then immobilized on Multiwall Carbon Nanotubes (Dex/MWCNT). By comparison of the normalized breakthrough curves measured for Dex and Dex/MWCNT on both the ACE2 and Main pro affinity columns, it was showed for the first time that nanovectorisation of Dex with MWCNT enhanced and stabilized its binding to both ACE2 and Main pro. This last result reinforced the use of Dex and the interest of MWCNT for boosting immune health against COVID 19.

Silanization of 3D-Printed Silica Fibers and Monoliths

Surface functionalization of complex three-dimensional (3D) porous architectures has not been widely investigated despite their potential in different application domains. In this work, silanization was performed in silica 3D-printed porous structures, and the homogeneity of functional groups within the architecture was investigated by comparing the extent of the functionalization in the walls and core of the monolith. A silica ink was used for direct ink writing (DIW) to shape fibers and monoliths with different architectures and stacking designs. The surfaces of the fibers and monoliths were functionalized with 3-aminopropyl(triethoxysilane) (APTES) using different reaction conditions. The nature of the functional groups on the surface and the presence of RSiO_1.5 bonds were identified by solid-state ¹³C-NMR, ²⁹Si-NMR, and by ξ-potential measurements. Elemental analysis was used to quantify the concentration of bonded APTES in the core and walls of the monolith. The availability and hydrolytic stability of the introduced amine group on fibers were evaluated using the adsorption of PdCl₄^2- ions within the pH range of 2-5. The study found that geometries with interfiber distances above 250 μm are homogeneously functionalized with amine groups. As the interfiber distance of the monolith decreases, a significantly lower density of amine groups is detected in the core of the monolith. The determination of the homogeneity of 3D-printed monoliths makes this work relevant as it provides the limits of functionalization carried out in stirred batch reactors for geometrically defined structures produced from a 3D-printing process.

Poly(acrylamide-co-N,N'-methylenebisacrylamide) Monoliths for High-Peak-Capacity Hydrophilic-Interaction Chromatography-High-Resolution Mass Spectrometry of Intact Proteins at Low Trifluoroacetic Acid Content

In this study, we optimized a polymerization mixture to synthesize poly(acrylamide-co-N,N′-methylenebisacrylamide) monolithic stationary phases for hydrophilic-interaction chromatography (HILIC) of intact proteins. Thermal polymerization was performed, and the effects of varying the amount of cross-linker and the porogen composition on the separation performance of the resulting columns were studied. The homogeneity of the structure and the different porosities were examined through scanning electron microscopy (SEM). Further characterization of the monolithic structure revealed a permeable (K_f between 2.5 × 10^–15 and 1.40 × 10^–13 m²) and polar stationary phase suitable for HILIC. The HILIC separation performance of the different columns was assessed using gradient separation of a sample containing four intact proteins, with the best performing stationary phase exhibiting a peak capacity of 51 in a gradient of 25 min. Polyacrylamide-based materials were compared with a silica-based particulate amide phase (2.7 μm core–shell particles). The monolith has no residual silanol sites and, therefore, fewer sites for ion-exchange interactions with proteins. Thus, it required lower concentrations of ion-pair reagent in HILIC of intact proteins. When using 0.1% of trifluoroacetic acid (TFA), the peak capacities of the two columns were similar (30 and 34 for the monolithic and packed column, respectively). However, when decreasing the concentration of TFA to 0.005%, the monolithic column maintained similar separation performance and selectivity (peak capacity 23), whereas the packed column showed greatly reduced performance (peak capacity 12), lower selectivity, and inability to elute all four reference proteins. Finally, using a mobile phase containing 0.1% formic acid and 0.005% TFA, the HILIC separation on the monolithic column was successfully hyphenated with high-resolution mass spectrometry. Detection sensitivity for protein and glycoproteins was increased and the amount of adducts formed was decreased in comparison with separations performed at 0.1% TFA.

Development of nano affinity columns for the study of ligand (including SARS-CoV-2 related proteins) binding to heparan sulfate proteoglycans

The interactions of heparan sulfate proteoglycans (HSPGs) present on the cell surface with target proteins lead to cell signaling and they are considered as viral receptors. The analysis of the recognition mechanism between HSPG and its potential ligands and high-throughput screening in drug discovery thus remain important challenges. Glycidyl methacrylate-based monoliths were thus prepared in situ in miniaturized capillary columns (internal diameter 75 μm) and HSPG was grafted onto them by the use of the Schiff base method. The quantity of grafted HSPG was in the nanogram range (11 nanograms per cm of capillary length). This is of significant importance when working with less available or expensive biological material. Other advantages of our miniaturized capillary column are as follows: (i) the immobilization process of HSPG onto the organic monolithic support was reliable and reproducible. (ii) The resultant affinity capillary column showed a strong resistance to changes in temperature and pH and a negligible non-specific interaction. So as to confirm the proper functioning of our miniaturized capillary column, the molecular recognition by HSPG of five selected compounds including three ligands of interest related to SARS-CoV-2 was studied.

Fabrication of polymer monoliths within the confines of non-transparent 3D-printed polymer housings

In the last decade, 3D-printing has emerged as a promising enabling technology in the field of analytical chemistry. Fused-deposition modelling (FDM) is a popular, low-cost and widely accessible technique. In this study, RPLC separations are achieved by in-situ fabrication of porous polymer monoliths, directly within the 3D-printed channels. Thermal polymerization was employed for the fabrication of monolithic columns in optically non-transparent column housings, 3D-printed using two different polypropylene materials. Both acrylate-based and polystyrene-based monoliths were created. Two approaches were used for monolith fabrication, viz. (i) in standard polypropylene (PP) a two-step process was developed, with a radical initiated wall-modification step 2,2'-azobis(2-methylpropionitrile) (AIBN) as the initiator, followed by a polymerization step to generate the monolith; (ii) for glass-reinforced PP (GPP) a silanization step or wall modification preceded the polymerization reaction. The success of wall attachment and the morphology of the monoliths were studied using scanning electron microscopy (SEM), and the permeability of the columns was studied in flow experiments. In both types of housings polystyrene-divinylbenzene (PS-DVB) monoliths were successfully fabricated with good wall attachment. Within the glass-reinforced polypropylene (GPP) printed housing, SEM pictures showed a radially homogenous monolithic structure. The feasibility of performing liquid-chromatographic separations in 3D-printed channels was demonstrated.

Confinement of Monolithic Stationary Phases in Targeted Regions of 3D-Printed Titanium Devices Using Thermal Polymerization

In this study, we have prepared thermally initiated polymeric monolithic stationary phases within discrete regions of 3D-printed titanium devices. The devices were created with controllable hot and cold regions. The monolithic stationary phases were first locally created in capillaries inserted into the channels of the titanium devices. The homogeneity of the monolith structure and the interface length were studied by scanning a capacitively coupled conductivity contactless detector (C4D) along the length of the capillary. Homogeneous monolithic structures could be obtained within a titanium device equipped with a hot and cold jacket connected to two water baths. The confinement method was optimized in capillaries. The sharpest interfaces (between monolith and empty channel) were obtained with the hot region maintained at 70 °C and the cold region at 4 or 10 °C, with the latter temperature yielding better repeatability. The optimized conditions were used to create monoliths bound directly to the walls of the titanium channels. The fabricated monoliths were successfully used to separate a mixture of four intact proteins using reversed-phase liquid chromatography. Further chromatographic characterization showed a permeability (Kf) of ∼4 × 10-15 m2 and a total porosity of 60%.

In-situ photopolymerized polyhedral oligomeric silsesquioxane-derived monolithic capillary columns with quinidine functionality for enantioseparation by nano-liquid chromatography

The successful fabrication of monolithic capillary columns for enantiomer separations was achieved within vinylized fused silica capillaries via fast "one-pot" photo-initiated free radical polymerization reaction. A mixture consisting of polyhedral oligomeric silsesquioxane, O-[2-(methacryloyloxy)ethylcarbamoyl]-10,11-dihydroquinidine was copolymerized in the presence of n-butanol, ethylene glycol and photo-initiator 2,2-dimethoxy-2-phenylacetophenone. The morphology of the resultant polymeric hybrid inorganic-organic material and its permeability as well as porosity can be controlled by adjusting the composition of the monomers and binary porogenic solvent. The chromatographic characteristics of the columns have been investigated. Separation factors of N-acetyl-phenylalanine (Ac-Phe) and dichlorprop dropped with decrease of chiral functional monomer. Permeability was better when the macroporogen ethyleneglycol was present at higher concentrations during the polymerization. In general, the chiral compounds were well separated (dichlorprop: α = 1.53, R_s up to 4.14; Ac-Phe: α = 1.36, R_s up to 2.69) by nano-HPLC with an optimized enantioselective monolithic capillary column which can be prepared within a few minutes.

Modulating Inflammation in Monocytes Using Capillary Fiber Organic Electronic Ion Pumps

An organic electronic ion pump (OEIP) delivers ions and drugs from a source, through a charge selective membrane, to a target upon an electric bias. Miniaturization of this technology is crucial and will provide several advantages, ranging from better spatiotemporal control of delivery to reduced invasiveness for implanted OEIPs. To miniaturize OEIPs, new configurations have been developed based on glass capillary fibers filled with an anion exchange membrane (AEM). Fiber capillary OEIPs can be easily implanted in proximity to targeted cells and tissues. Herein, the efficacy of such a fiber capillary OEIP for modulation of inflammation in human monocytes is demonstrated. The devices are located on inflammatory monocytes and local delivery of salicylic acid (SA) is initiated. Highly localized SA delivery results in a significant decrease in cytokine (tumor necrosis factor alpha and interleukin 6) levels after lipopolysaccharide stimulation. The findings-the first use of such capillary OEIPs in mammalian cells or systems-demonstrate the utility of the technology for optimizing transport and delivery of different therapeutic substances at low concentrations, with the benefit of local and controlled administration that limits the adverse effect of oral/systemic drug delivery.

Overcoming transport limitations in miniaturized electrophoretic delivery devices

Organic electronic ion pumps (OEIPs) have been used for delivery of biological signaling compounds, at high spatiotemporal resolution, to a variety of biological targets. The miniaturization of this technology provides several advantages, ranging from better spatiotemporal control of delivery to reduced invasiveness for implanted OEIPs. One route to miniaturization is to develop OEIPs based on glass capillary fibers that are filled with a polyelectrolyte (cation exchange membrane, CEM). These devices can be easily inserted and brought into close proximity to targeted cells and tissues and could be considered as a starting point for other fiber-based OEIP and "iontronic" technologies enabling favorable implantable device geometries. While characterizing capillary OEIPs we observed deviations from the typical linear current-voltage behavior. Here we report a systematic investigation of these irregularities by performing experimental characterizations in combination with computational modelling. The cause of the observed irregularities is due to concentration polarization established at the OEIP inlet, which in turn causes electric field-enhanced water dissociation at the inlet. Water dissociation generates protons and is typically problematic for many applications. By adding an ion-selective cap that separates the inlet from the source reservoir this effect is then, to a large extent, suppressed. By increasing the surface area of the inlet with the addition of the cap, the concentration polarization is reduced which thereby allows for significantly higher delivery rates. These results demonstrate a useful approach to optimize transport and delivery of therapeutic substances at low concentrations via miniaturized electrophoretic delivery devices, thus considerably broadening the opportunities for implantable OEIP applications.

Smart blood spots for whole blood protein analysis

A reactor for whole blood sampling integrated with instant protein digestion in a “lab-on-paper” format is introduced here.

Controlled crosslinking of trimethylolpropane trimethacrylate for preparation of organic monolithic columns for capillary liquid chromatography

Organic monolithic columns based on single crosslinking of trimethylolpropane trimethacrylate (TRIM) monomer were prepared in a single step by living/controlled free-radical polymerization. Full optimization of the preparation, such as using different percentages of TRIM and different amounts of radical promoter as well as various porogen solvents were explored. The resulting monolithic columns were characterized by scanning electronic microscopy and nitrogen sorption for structure morphology studies and surface area measurements, respectively. Using capillary liquid chromatography, 150 μm i.d. columns were applied to separate a mixture of small hydrophobic molecules. The results indicated that column performance is highly sensitive to the type and the amount of porogen solvents used in the polymerization mixture composition. Good resolution factors and methylene selectivity were obtained, indicating the promising potential of this material for capillary liquid chromatography separations.

Improvement in Liquid Chromatographic Performance of Organic Polymer Monolithic Capillary Columns with Controlled Free-Radical Polymerization

Capillary columns containing butyl or lauryl methacrylate monoliths were prepared using two different free-radical polymerization methods: conventional free-radical polymerization and controlled/living free-radical polymerization, both initiated thermally, and these methods were compared for the first time. Both monolith morphology and chromatographic efficiency were compared for the synthesized stationary phases using scanning electronic microscopy (SEM) and capillary liquid chromatography, respectively. Columns prepared using controlled method gave better chromatographic performance for both monomers tested. The lauryl-based monolith showed 7-fold improvement in chromatographic efficiency with a plate count of 42,000 plates/m (corrected for dead volume) for a non-retained compound. Columns fabricated using controlled polymerization appeared more homogenous radially with fused small globular morphologies, evaluated by SEM, and lower column permeability. The columns were compared with respect to resolving power of a series of alkylbenzenes under isocratic and gradient elution conditions.

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.

Cationic pTyr/pSer imprinted polymers based on a bis-imidazolium host monomer: phosphopeptide recognition in aqueous buffers demonstrated by μ-liquid chromatography and monolithic columns

Capillary monoliths featuring grafted molecularly imprinted polymer films incorporating on a bis-imidazolium host monomer, displayed a remarkable crossreactivity with phosphorylated peptides in buffered media.

Different Stationary Phase Selectivities and Morphologies for Intact Protein Separations

The central dogma of biology proposed that one gene encodes for one protein. We now know that this does not reflect reality. The human body has approximately 20,000 protein-encoding genes; each of these genes can encode more than one protein. Proteins expressed from a single gene can vary in terms of their post-translational modifications, which often regulate their function within the body. Understanding the proteins within our bodies is a key step in understanding the cause, and perhaps the solution, to disease. This is one of the application areas of proteomics, which is defined as the study of all proteins expressed within an organism at a given point in time. The human proteome is incredibly complex. The complexity of biological samples requires a combination of technologies to achieve high resolution and high sensitivity analysis. Despite the significant advances in mass spectrometry, separation techniques are still essential in this field. Liquid chromatography is an indispensable tool by which low-abundant proteins in complex samples can be enriched and separated. However, advances in chromatography are not as readily adapted in proteomics compared to advances in mass spectrometry. Biologists in this field still favour reversed-phase chromatography with fully porous particles. The purpose of this review is to highlight alternative selectivities and stationary phase morphologies that show potential for application in top-down proteomics; the study of intact proteins.

Fabrication of a GMA-co-EDMA Monolith in a 2.0 mm i.d. Polypropylene Housing

Polymers are interesting housing materials for the fabrication of inexpensive monolithic chromatography and solid phase extraction (SPE) devices. Challenges arise when polymeric monoliths are formed in non-conical, cylindrical tubes of larger diameter due to potential monolith detachment from the housing wall resulting in loss of separation performance and mechanical stability. Here, a two-step protocol is applied to ensure formation of robust homogeneous methacrylate monolith in polypropylene (PP) tubing with a diameter of 2.0 mm. Detailed Fourier-transform infrared (FTIR) spectroscopic analysis and Scanning Electron Microscopy (SEM) imaging confirm the successful pre-modification of the tubing wall with an anchoring layer of cross-linked ethylene dimethacrylate (EDMA). Subsequent formation of an EDMA-glycidyl methacrylate (GMA) monolith in the PP tube resulted in a homogeneous monolithic polymer with enhanced mechanical stability as compared to non-anchored monoliths.

Fabrication of a polymer nozzle array in a microstructured fibre as a nanoelectrospray emitter for mass spectrometry

We report a modified silica microstructured fibre (MSF) as a multiple electrospray (MES) emitter, with dimensional compatibility with conventional liquid chromatography and mass spectrometry equipment, to generate stable electrospray from a wide range of applied potentials and flow rates. An array of polymer nozzles is fabricated in the MSF by a procedure involving templated polymerization of microtubes and wet chemical etching of the silica at the tip. The structure of the emitting end of the MSF was optimized with respect to the etching process, and the morphology of the polymer nozzles was optimized with respect to polymerization conditions. The mechanisms of the etching and of the templated polymerization of the microtubes were explored. Optimization experiments were performed using commercially available MSF having 126 tubular air channels arranged in a hexagonal pattern with channel diameter of ∼5.6 μm. However, the flexibility and versatility in the pattern, shape, and size of channels in MSFs allowed a custom-designed MSF to be fabricated and tested for MES. In the new design, six channels were evenly spaced in a radial pattern, and when polymer nozzles were made, six stable electrosprays were observed over a wide range of electrospray conditions. Using these MES emitters, the spray current is enhanced by a factor related to the number of nozzles.

Post-polymerization photografting on methacrylate-based monoliths for separation of intact proteins and protein digests with comprehensive two-dimensional liquid chromatography hyphenated with high-resolution mass spectrometry

Post-polymerization photografting is a versatile tool to alter the surface chemistry of organic-based monoliths so as to obtain desired stationary phase properties. In this study, 2-acrylamido-2-methyl-1-propanesulfonic acid was grafted to a hydrophobic poly(butyl methacrylate-co-ethylene glycol dimethacrylate) monolith to create a strong cation exchange stationary phase. Both single-step and two-step photografting were addressed, and the effects of grafting conditions were assessed. An experimental design has been applied in an attempt to optimize three of the key parameters of the two-step photografting chemistry, i.e. the grafting time of the initiator, the monomer concentration and the monomer irradiation time. The photografted columns were implemented in a comprehensive two-dimensional column liquid chromatography (^tLC × ^tLC) workflow and applied for the separation of intact proteins and peptides. A baseline separation of 11 intact proteins was obtained within 20 min by implementing a gradient across a limited RP composition window in the second dimension. ^tLC × ^tLC with UV detection was used for the separation of cytochrome c digest, bovine serum insulin digest and a digest of a complex protein mixture. A semi-quantitative estimation of the occupation of separation space, the orthogonality, of the ^tLC × ^tLC system yielded 75 %. The ^tLC × ^tLC setup was hyphenated to a high-resolution Fourier transform ion cyclotron resonance mass spectrometer instrument to identify the bovine serum insulin tryptic peptides and to demonstrate the compatibility with MS analysis.

Preparation of monolithic affinity media for nano-liquid chromatography applications

In this protocol, a strategy is described for preparing affinity media with monolithic materials as stationary phase, which is exemplified for the biotin-avidin interaction pair. The capillary columns prepared in this manner are compatible with nano-liquid chromatographic conditions. Our protocol is easily adapted to the preparation of specific affinity media with different functionalities and as such provides a platform for a multitude of applications.

Photografting as a versatile, localizable, and single-step surface functionalization of silica-based monoliths dedicated to microscale separation techniques

In this work, we developed a surface functionalization way of silica monoliths with a rapid, simple, versatile, and localizable photografting step. The elaboration of a photoreactive layer at the surface of monoliths was first optimized. The functionalization with [γ-(methacryloyloxy)propyl]trimethoxysilane at 80°C in a hydro-organic solution containing triethylamine as catalyst allows reachng the highest density of methacrylate photoactive moieties on silica surfaces. These methacrylate reactive surfaces were subsequently photografted within few minutes with acrylate monomers bearing alkyl chains (C12 and C18). The photografting efficiency was determined by monitoring the retentive properties of monoliths in the RP mode. The retention factors are of the same order of magnitude as highly retentive columns obtained by modification of silica surface with long-alkyl chain silanes or by thermal polymerization of long-alkyl chain monomers. It was also verified that such grafting neither impaired the efficiency of the monolithic stationary phase (Hmin = 6-8 μm in nano-LC) nor its permeability (about 6 × 10(-14) m(2)). Further, it was also demonstrated that photografting is localizable in nonmasked defined areas. Results obtained in anion-exchange chromatography after photopolymerization of [2-(methacryloyloxy)ethyl]trimethylammonium chloride are presented as well to demonstrate the versatility of the developed approach.