Packing Materials For Chromatography Research Articles

Glycopolymer Grafted Silica Gel as Chromatographic Packing Materials.

The modification of the surface of silica gel to prepare hydrophilic chromatographic fillers has recently become a research interest. Most researchers have grafted natural sugar-containing polymers onto chromatographic surfaces. The disadvantage of this approach is that the packing structure is singular and the application scope is limited. In this paper, we explore the innovative technique of grafting a sugar-containing polymer, 2-gluconamidoethyl methacrylamide (GAEMA), onto the surface of silica gel by atom transfer radical polymerization (ATRP). The SiO2-g-GAEMA with ATRP reaction time was characterized by Fourier infrared analysis, Thermogravimetric analysis (TGA), and elemental analysis. As the reaction time lengthened, the amount of GAEMA grafted on the surface of the silica gel gradually increased. The GAEMA is rich in amide bonds and hydroxyl groups and is a typical hydrophilic chromatography filler. Finally, SiO2-g-GAEMA (reaction time = 24 h) was chosen as the stationary phase of the chromatographic packing and evaluated with four polar compounds (uracil, cytosine, guanosine, and cytidine). Compared with unmodified silica gel, modified silica gel produces sharper peaks and better separation efficiency. This novel packing material may have a potential for application with highly isomerized sugar mixtures.

Online measurement of phthalate–particulate matter interactions by membrane introduction mass spectrometry (MIMS)

ABSTRACTTo enable further study and assessment of indoor inhalation exposure risk, an online apparatus enabling measurement of semi-volatile compound partitioning on household particulates was developed. An example for use of the apparatus is described using dimethyl phthalate (DMP). The system employs direct measurement by membrane introduction mass spectrometry (MIMS). The MIMS system was calibrated using known gas phase DMP concentrations produced by gravimetrically calibrated permeation devices. The quantity of DMP sorbed by particles is described first using a model particle type, a reverse-phase liquid chromatography packing material, and then with a household dust sample. In addition, the desorption of semi-volatile compounds from a household dust sample was monitored using the apparatus, and characteristic fragment ion signals for phthalate compounds were observed.

Light-assisted preparation of vancomycin chiral stationary phase based on diazotized silica and its enantioseparation evaluation by high-performance liquid chromatography

Owing to enantiomers’ identical physical and chemical properties, separation work in the chiral environments is still a great challenge.and chemical properties. Chromatographic techniques employing chiral stationary phases (CSPs) have been developed as powerful tools for the chiral analysis and preparation of pure enantiomers. Here we report a facile synthesis of vancomycin stationary phase based on diazotized silica. Monodisperse silica particles were synthesized by a modified Stöber method. The obtained silica particles were modified by self-assembly photosensitive diazoresin (DR) and vancomycin on the surface. After treatment with UV light, the ionic bonding was converted into covalent bonding through a unique photochemistry reaction of DR. Baseline separation of chiral drugs was achieved by using the vancomycin@SiO2 particles as packing materials in high performance liquid chromatography (HPLC). The effects of separation parameters including elution mode, flow rate and analyte mass on the enantioselectivity of the CSP were investigated in detail. Due to the replacement of highly toxic and moisture sensitive silane agent by water soluble non-toxic DR in the modification of silica microspheres, this method provides a green and easy way to manufacture packing materials for chromatography applications.

Novel reversed-phase/weak-cation-exchange mixed-mode chromatographic packing materials applied in mass-spectrometry-based proteomics

High efficiency separation plays a key role in deep-coverage proteomics studies. In this study, we investigate a mixed-mode chromatographic packing material and use “thiol-ene” click chemistry to prepare a novel reversed-phase/weak-cation-exchange mixed-mode chromatographic packing material. First, we used a mixture of chemical compounds with low molecular weights to characterize the packing material and the results showed that it has both reversed-phase and weak-cation-exchange chromatographic retention mechanisms. Next, we used the reversed-phase/weak-cationic-exchange mixed-mode chromatographic stationary phase in the separation of a mixture of six standard peptides with similar hydrophobicities but with different theoretical isoelectric points. The experimental results showed that the packing materials have a mixed-mode retention performance. We also found that the hydrophilic properties of the embedded functional groups play an important role in decreasing the hydrophobicity of the packing material and therefore reduces the loss of some of the peptides due to the strong adsorption of very high hydrophobic peptides. Lastly, we selected an off-line RP/WCX column with a pH gradient elution as the first dimension for pre-separation and employed reversed-phase liquid chromatography (RPLC)-mass spectrometry analysis as the second dimension for the analysis of the protein mixture of 100-µg HepG2 cells. In total, we identified 5924 proteins. These results are similar to those obtained by the RPLC-mass spectrometry analysis commonly used in proteome research, which suggests that this mixed-mode chromatographic packing material can be used in proteomics research.

Specific recognition of polyphenols by molecularly imprinted polymers based on a ternary deep eutectic solvent

Typically, a target compound is selected as a template for a molecularly imprinted polymer (MIP); however, some target compounds are not suitable as templates because of their poor solubility. Using the tailoring properties of a deep eutectic solvent (DES), the insoluble target compound caffeic acid was transformed into a ternary choline chloride–caffeic acid–ethylene glycol (ChCl–CA–EG) DES, which was then employed as a template to prepare MIPs. The ternary DES-based MIPs were characterized by Fourier transform infrared spectroscopy, elemental analysis, scanning electron microscopy, and atomic force microscopy. The effects of time, temperature, ionic strength, and pH on the recognition processes for four polyphenols (caffeic acid, protocatechuic acid, catechin, and epicatechin) by 13 ChCl–CA–EG ternary DES-based MIPs was investigated using high-performance liquid chromatography. The recognition specificity of the MIPs for CA was significantly better than that for the other polyphenols, and the MIPs exhibited obvious characteristics of chromatographic packing materials. In addition, the recognition processes mainly followed a second-order kinetics model and the Freundlich isotherm model, which together indicated that the MIPs mainly recognized the polyphenols by chemical interactions including ion exchange, electron exchange, and new bond formation. Furthermore, the specific recognition ability of the MIPs for polyphenols, which was better than those of C18, C8, or non-molecularly imprinted polymer adsorbents, was successfully applied to the recognition of polyphenols in a Radix asteris sample. The transformation of an insoluble target compound in a polymeric DES for MIP preparation and recognition is a novel and feasible strategy suitable for use in further MIP research developments.

Synthesis of monodisperse silica microspheres and modification with diazoresin for mixed-mode ultra high performance liquid chromatography separations.

Monodisperse silica particles with average diameters of 1.9-2.9 μm were synthesized by a modified Stöber method, in which tetraethyl orthosilicate was continuously supplied to the reaction mixture containing KCl electrolyte, water, ethanol, and ammonia. The obtained silica particles were modified by self-assembly with positively charged photosensitive diazoresin on the surface. After treatment with ultraviolet light, the ionic bonding between silica and diazoresin was converted into covalent bonding through a unique photochemistry reaction of diazoresin. Depending on the chemical structure of diazoresin and mobile phase composition, the diazoresin-modified silica stationary phase showed different separation mechanisms, including reversed phase and hydrophilic interactions. Therefore, a variety of baseline separation of benzene analogues and organic acids was achieved by using the diazoresin-modified silica particles as packing materials in ultra high performance liquid chromatography. According to the π-π interactional difference between carbon rings of fullerenes and benzene rings of diazoresin, C60 and C70 were also well separated by ultra-high performance liquid chromatography. Because it has a small size, the ∼2.5 μm monodisperse diazoresin-modified silica stationary phase shows ultra-high efficiency compared with the commercial C18 -silica high-performance liquid chromatography stationary phase with average diameters of ∼5 μm.

Synthesis of Mesoporous Siliceous Materials in Choline Chloride Deep Eutectic Solvents and the Application of These Materials to High-Performance Size Exclusion Chromatography

Mesoporous materials were prepared in choline chloride deep eutectic solvents by triblock copolymer-templated hydrothermal synthesis. The mesoporous materials were characterized by thermogravimetric analysis, scanning electron microscopy and nitrogen sorption analysis. The mesoporous material-based choline chloride-ethylene glycol (1:2 mol ratio) deep eutectic solvent had a flower-type shape, but the material-based choline chloride-urea (1:2) and based choline chloride-acetic acid (1:2) had mesoporous spherical shapes. These mesoporous materials were applied to high-performance size exclusion chromatography column packing. The separation effect of the two dextrans was better from the choline chloride-acetic acid deep eutectic solvent-based mesoporous spheres packed in a high-performance size exclusion chromatography column. In addition, the three polysaccharides, dextran-1 (molecular weight: 670 KD), dextran-2 (molecular weight: 50 KD) and dextran-3 (molecular weight: 5 KD), were separated successfully using the choline chloride-acetic acid deep eutectic solvent-based mesoporous spheres packed in a high-performance size exclusion chromatography column. The mesoporous spheres-based deep eutectic solvents are a potential packing material in high-performance size exclusion chromatography. The separation conditions of more target compounds will be explored in future studies.

Exploration of Mesoporous Stationary Phases Prepared Using Deep Eutectic Solvents Combining Choline Chloride with 1,2-Butanediol or Glycerol for Use in Size-Exclusion Chromatography

Mesoporous siliceous particles were prepared using deep eutectic solvents (DESs)—either choline chloride and 1,2-butanediol in a 1:2 molar ratio (ChCl-B) or choline chloride and glycerol in a 1:2 molar ratio (ChCl-G)—and then tested as column packing materials in size-exclusion chromatography (SEC). When they were tested as column packing materials in SEC of a mixture of two dextrans with different molecular weights using a methanol mobile phase, the ChCl-G-based particles were not able to separate the dextrans, whereas the ChCl-B-based particles provided good separation (considerably better than that afforded by traditional sorbents) at a flow rate of 0.3 mL min−1. This high separating power of the ChCl-B-based particles can be attributed to the utilization of the DES ChCl-B during their preparation.

A reversed-phase/hydrophilic interaction mixed-mode C18-Diol stationary phase for multiple applications

A mixed-mode chromatographic packing material, C18 and diol groups modified silica (C18-Diol), was prepared with controllable hydrophobicity and hydrophilicity. It demonstrated excellent aqueous compatibility and stability in aqueous mobile phase; compared to the traditional C18 column, improved peak shape of basic analytes was also obtained. Additionally, it exhibited both reversed-phase liquid chromatographic (RPLC) and hydrophilic interaction chromatographic (HILIC) performance; the analyte separation scope was thus enlarged, demonstrated by simultaneous separation of twenty acids, bases and neutrals. More interestingly, a novel on-line two-dimensional liquid chromatography on the single column (2D-LC-1C) was established by modifying the high performance liquid chromatographic instrument only with the addition of an extra six-port two-position valve. The early co-eluted components of the extract of Lonicera japonica on the 1st-dimension (RPLC) were collected for the online re-injection to the 2nd-dimension (HILIC) by conveniently varying the mobile phase components. Six more peaks were obtained. The established system was simple, easy operation and low cost, which had advantages in analyzing complicated samples.

New Materials Applied for the Stationary Phases in View of the Optimized HPLC and UHPLC Column Classification System Used in the Pharmaceutical Analysis

Pharmacopoeial monographs define usually requirements for the use of the particular chromatographic packing materials in a very general way. Even if a selection of particular chromatographic column packed with the defined material is suggested, it appears often that column is currently not present in the laboratory, or is no longer commercially available. With respect to those facts, there are needs to replace the given column material for another one, however with the similar physicochemical characteristics. This can be achieved by using one of the classification systems of columns’ material (e.g., the procedure developed by the researchers at the Katholieke Universiteit Leuven – and therefore called tentatively by us as KUL procedure).In the first stage of the work, it has been proven that the results obtained by KUL procedure can be related to results obtained during chemometrics verification of the suitability of selected stationary phases’ material used in the individual columns for purity test of alfuzosin as pharmaceutical substance and their impurities and related compounds. The next step was to adapt KUL procedure to allow the classification of modern and new UHPLC and Core-Shell (CS) columns’ material characterized by the novel physicochemical properties. Together, properties of 61 columns packed with variable materials have been characterized. The last step comprised the data collection to examine the possibilities to use UHPLC and CS columns materials as equivalent ones to the classical HPLC columns’ materials in view of the method transfer for the previously mentioned assay for alfuzosin.

Exploration of deep eutectic solvent‐based mesoporous silica spheres as high‐performance size exclusion chromatography packing materials

ABSTRACTCholine chloride (ChCl) with three alcohol‐based deep eutectic solvents (DESs) was applied as a new type of green solvent for the modification of mesoporous silica spheres. The mesoporous silica spheres were characterized by field emission scanning electron microscopy and Brunauer–Emmett–Teller surface area analysis. Many uniform and mesoporous silica spheres were obtained with a ChCl–1,2‐butanediol DES as a reactant. The DES‐modified mesoporous silica spheres were used for the adsorption of polysaccharides (alginic acid, fucoidan, and laminarin). The adsorption results show that the ChCl–1,2‐butanediol DES‐based silica spheres had stable interactions with the target compounds. A comparison of the three sorbents as size exclusion chromatography packing materials showed that the ChCl–1,2‐butanediol DES‐based silica spheres produced good resolution of the three test polysaccharides and exhibited the best separation capability. This was attributed to the uniform mesoporous structure of the ChCl–1,2‐butanediol DES‐based silica spheres. Therefore, more DESs should be applied to the preparation of mesoporous silica spheres in future studies. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42203.

Developing a new and versatile ordered mesoporous organosilica as a pH and temperature stable chromatographic packing material

Periodic Mesoporous Organosilicas (PMOs) have been successfully spray dried for the first time using a novel cyclic multifunctional organosilane molecule.

One-step synthesis of sub-2 μm vinyl functionalized silica sphere as stationary phase for liquid chromatography

Vinyl-functionalized silica spheres (VFSS) were synthesized through the one-step method. The effects of reactant ratio, temperature, reaction time and ammonium hydroxide dripping speed were investigated. The diameter of the spheres reached sub-2μm magnitude by controlling the reaction conditions, which is suitable for high performance liquid chromatography (HPLC) packing material. The vinyl groups in the silica spheres were further successfully modified by octadecyl (C18) groups through a “thiol-ene” click reaction. Raw VFSS and C18modified VFSS (C-VFSS) were used as HPLC stationary phases to separate benzene homologs (benzene, toluene, and meta-xylene) and nonpolar compounds with different ring contents (benzene, phenantherene and fluoranthene). Both VFSS and C-VFSS exhibited hydrophobic retention behavior. Additionally, vinyl groups in the silica spheres may offer a π–π electron–donor–acceptor (EDA) retention mechanism for chromatographic separation.

Investigation of porous structure of packing materials based on 1‐vinyl‐2‐pyrrolidone

Highly crosslinked copolymers of 1‐vinyl‐2‐pyrrolidone (VP) were obtained in the form of microspheres by combined suspension–emulsion polymerization. The porous structure of the copolymers was created by the use of proper diluents. The main parameters of porous structure were established in the dry and wet states. Three methods: inverse size‐exclusion chromatography (ISEC), nitrogen adsorption, and small X‐ray scattering (SAXS) were used in porous structure investigations. It was shown that the determined parameters strongly depend on the chosen method and the microspheres can be used as packing materials in chromatography. Copyright © 2014 John Wiley & Sons, Ltd.

Evaluation of preparative hydrodynamic chromatography of silica stationary phase supports

Reducing the particle size distribution (PSD) of sub-2μm chromatographic packing materials can improve the performance of capillary UHPLC columns, but several size refinement methods are only partially effective in this size range. To this end, a preparative scale hydrodynamic chromatography (HDC) method was developed to size-refine C18 functionalized sub-2μm particles, but suffered from poor reproducibility and particle aggregation issues. Presented here are improvements based on the use of an ammonium hydroxide as the mobile phase. This mobile phase makes the method reproducible, decreases column conditioning requirements, and focuses on the preparation of bare silica material which allows for a wider variety of stationary phase bondings. Additionally, particle recovery for both non-porous silica size standards and bridged-ethyl hybrid (BEH) particles are detailed to highlight the advantages of this method. The data presented demonstrates the capability of this method to reduce the relative standard deviation (RSD) of the PSD of BEH particles by 33% in under 2h with sufficient yield to pack several capillary columns.

Preparation and Characterization TiO2 Microspheres for the Liquid Chromatography Stationary Phase

TiO2 microspheres with a uniform particle size distribution were synthesized by hydrothermal method. After being sintered, the titania microspheres that are obtained have an average diameter of 5 μm, a surface area of 383.5 m2/g, an average pore volume of 0.25 cm3/g, and an average pore diameter of 35.9 nm. Normal phase chromatography was separated the mixture of benzene, nitrobenzene and nitro-anisole, three substances were separated well on the titania column. The microspheres possess enough rigidity to withstand high packing pressure and are very useful as a new kind of chromatographic packing material for high performance liquid chromatography (HPLC).

Restricted access media as a streamlined approach toward on‐line sample preparation: Recent advancements and applications

Restricted access media (RAM) as an alternative to traditional sample preparation strategies are reviewed. RAM comprise chromatographic packing materials that combine, typically, a restrictive outer surface to exclude the retention of large biomolecules, which are common interferences in biological fluids, with retentive inner pores or phases to capture analytes of interest. Through the years, a variety of RAM formats have been created, including internal surface phases, semipermeable phases, and molecularly imprinted polymer phases. Many phases are commercially available through a variety of manufacturers. The use of on-line sample preparation using RAM can increase throughput, recovery, and ease of use for sample preparation of complex biological matrices. The state-of-the-art with respect to production and use of these media for a variety of applications is covered.

Plastic LC/MS microchip with an embedded microstructured fibre having the dual role of a frit and a nanoelectrospray emitter

Integrating functionality on a microfluidic platform, such as a frit or electrospray emitter for coupling with a mass spectrometer, can be complicated, costly, and introduce dead volume deleterious to liquid chromatography (LC). Here, we demonstrate the fabrication of a LC/MS microchip device with an integrated nanoelectrospray emitter that also functions as a retaining frit. The integrated emitter effectively minimizes dead volume associated with coupling the device externally to MS with electrospray ionization and complications associated with frit microfabrication. The emitter is made of microstructured optical fibre, which has an array of equivalent parallel channels. The size and spacing of these channels make the fibre amenable to retaining chromatographic packing material while simultaneously performing as a nanoelectrospray emitter. The chromatographic chip is fashioned from cyclic olefin copolymer (Zeonor) using hot embossing and thermal/solvent bonding techniques. The device is fabricated in less than 3 h with simple technique and low-cost materials while maintaining sufficient solvent resistance and mechanical strength, withstanding pressure drops of up to 100 bar. This microchip was used to effectively separate small drug molecules by isocratic elution and larger peptides using gradient elution. Robustness of the plastic LC/MS devices was demonstrated by frequent use over several months with consistent results. Such devices represent a practical approach to the facile integration of a frit and/or an ESI emitter in a microfluidic device at low cost while minimizing dead volume associated with coupling the chip to MS.

Synthesis and evaluation of molecularly imprinted polymeric microspheres for highly selective extraction of an anti-AIDS drug emtricitabine

The molecularly imprinted polymeric microspheres (MIPMs, 3~5 μm), used as high-performance liquid chromatography (HPLC) and solid-phase extraction (SPE) packing materials for anti-AIDS drug emtricitabine (FTC), were synthesized by precipitation polymerization. The effects of ratio of chloroform to acetonitrile on the morphology and diameter of MIPMs were investigated. The prepared MIPMs were characterized by HPLC. The imprinting factor (2.26) suggests that the resultant MIPMs exhibit good recognition and affinity to FTC. In addition, the MIPMs were used in SPE as packing material for separation and enrichment of FTC. The recovery of FTC on MIPMs cartridge was 97.6 % in standard solution. Finally, the MIPMs cartridge was applied to extract the FTC in human serum samples. Impurities in sample have been mostly removed, and the average recovery of 92.5 % was obtained with a detection limit of 0.005 μg/mL and a linear range of 0.02~4.0 μg/mL. The method established can be used to monitor the FTC in human serum sample with good accuracy and selectivity.

Novel Composite Materials for Chiral Separation from Cellulose and Barium Sulfate

Cellulose was dissolved in an aqueous solution of sodium hydroxide (NaOH) and urea followed by the addition of barium sulfate (BaSO4) to yield the BaSO4/cellulose composite particles. The morphology, particle size, and BaSO4content of the composite particles were adjusted by controlling the feed ratio of cellulose and BaSO4. The cellulose within the composite particles then reacted with 3,5-dimethylphenyl isocyanate. The resulting materials were utilized as the chiral stationary phases (CSPs) whose enantioseparation capabilities were evaluated by various chiral analytes. Due to the mechanical enhancement effect of BaSO4, the composite particles could be applied to the chromatographic packing materials.