Ligai Bai

Fabrication of an ionic liquid-based macroporous polymer monolithic column via atom transfer radical polymerization for the separation of small molecules

A polymer monolithic column was prepared in a stainless steel column (50×4.6mm i.d.) via atom transfer radical polymerization technique using triallyl isocyanurate and ionic liquid (1-allyl-3-methylimidazolium chloride) as co-monomers, ethylene dimethacrylate as cross linking agent, polyethylene glycol 200, 1,4-butanediol, and N, N- dimethylformamide as porogen system, CCl4 as initiator, and FeCl2 as catalyst. The optimized polymer columns were characterized by scanning electron microscope, nitrogen adsorption-desorption instrument, mercury intrusion porosimetry, infrared spectrometer, and thermogravimetric analysis technique. Respectively, all of these factors above could illustrate that the optimized columns had relative uniform macroporous structure and high thermal stability. A series of basic and acidic small molecules, isomers, and homologues were used to evaluate the performance of these monoliths and enhanced column efficiency was obtained.

Incorporation of ionic liquid into porous polymer monoliths to enhance the separation of small molecules in reversed-phase high-performance liquid chromatography

An ionic liquid was incorporated into the porous polymer monoliths to afford stationary phases with enhanced chromatographic performance for small molecules in reversed-phase high-performance liquid chromatography. The effect of the ionic liquid in the polymerization mixture on the performance of the monoliths was studied in detail. While monoliths without ionic liquid exhibited poor resolution and low efficiency, the addition of ionic liquid to the polymerization mixture provides highly increased resolution and high efficiency. The chromatographic performances of the monoliths were demonstrated by the separations of various small molecules including aromatic hydrocarbons, isomers, and homologues using a binary polar mobile phase. The present column efficiency reached 27 000 plates/m, which showed that the ionic liquid monoliths are alternative stationary phases in the separation of small molecules by high-performance liquid chromatography.

On-line solid phase extraction using organic-inorganic hybrid monolithic columns for the determination of trace β-lactam antibiotics in milk and water samples.

A rapid and simple method with on-line solid phase extraction (SPE) has been developed for the simultaneous determination of beta-lactam antibiotics (BLAs) (amoxicillin, cephradine, and cefazolin sodium) in aquatic environment and milk. The epoxy-based organic-inorganic hybrid monolithic column was used as SPE sorbent to simultaneously monitor three analytes. The morphology of monolithic column and pressure drop across the columns were characterized. Excellent permeability and high selectivity were obtained. The linear range of the standard curve was from 2.0 to 500 ng/mL (r(2)≥0.999). Precision for inter- and intra-day assay showed acceptable results for quantitative assay with relative standard deviation (RSD) less than 11%. The accuracy and recovery were found to be within the range of 93-103% and 83-105%. The results indicated that the prepared monolithic column could provide excellent reproducibility and implied that the prepared monolith was feasible to be used as an on-line SPE sorbent material.

Hydrophilic molecularly imprinted melamine-urea-formaldehyde monolithic resin prepared in water for selective recognition of plant growth regulators

New hydrophilic molecularly imprinted melamine-urea-formaldehyde monolithic resin (MIMR) is synthesized using dopamine hydrochloride as a dummy template via in-situ polymerization directly within pipette tips and it presents special molecular recognition to plant growth regulators in aqueous matrices. Hydrophilic groups (such as hydroxyl groups, imino groups, and amino groups) can be introduced into MIMR by melamine- urea-formaldehyde resin, which make MIMR materials compatible with aqueous media and show their specific molecular recognition in aqueous sample solutions. Meanwhile, monolithic structures avoid the influence of uneven filling on the extraction efficiency. Various parameters affecting the selective recognition of MIMR have been optimized, such as molar ratio of melamine to urea, molar ratio of melamine and urea to formaldehyde, the amount of template and porogen. The prepared MIMR is applied as the sorbents of solid phase extraction (SPE) for sensitive and selective recognition of three plant growth regulators (p-chlorophenoxyacetic acid, 1-naphthaleneacetic acid and 2.4-dichlorophenoxyacetic acid) in bean sprouts. Considering its excellent hydrophilicity and specificity, MIMR-SPE is promising to be a potential pretreatment strategy in biological, environmental, and clinical fields.

A novel ionic liquid-based monolithic column and its application in the efficient separation of proteins and small molecules by high-performance liquid chromatography

A novel skeleton porous polymer-based monolith chromatography column has successfully been prepared using an in situ free radical polymerization technique. A 50 mm × 4.6 mm i.d. stainless steel chromatographic column used dodecanol as porogen and ionic liquid (IL), 1-dodecene (C12) and trimethylol propane triacrylate (TMPTA) as monomers, and ethylene dimethacrylate as crosslinker. The effect of variables such as temperature and porogen solvent content on the porous structure was studied in detail. The polymer-based monolith obtained was characterized by scanning electron microscopy, infrared spectroscopy, mercury intrusion porosimetry, and nitrogen adsorption. The results indicated that the monolithic column had a porous structure, good mechanical stability, high permeability (6.77 × 10−14 m2), and a high specific surface area (155.62 m2 g−1). The liquid chromatographic performance of the monolith was evaluated in the separation of lysozyme from egg white and in the separation of a variety of mixtures of small molecules, such as amines and benzene analogues. The column showed good repeatability and reproducibility, and the column-to-column (n = 7) and batch-to-batch (n = 5) reproducibility was 2.85 and 3.15%, respectively.

Ionic liquid as porogen in the preparation of a polymer-based monolith for the separation of protein by high performance liquid chromatography

A novel polymer-based monolith for high performance liquid chromatography was fabricated via atom transfer radical polymerization without the expensive complexing ligand, in which methyl methacrylate was used as the monomer, vinyl ester resin as a cross-linker, 1-butyl-3-methylimidazolium chloride/dodecanol as the porogen, carbon tetrachloride as the initiator and ferrous chloride as the catalytic agent. The morphology of the monolith was studied using scanning electronic microscopy. The chemical groups of the monolith were assayed using the infrared spectroscopy method. The pore size distribution was determined using a mercury porosimeter and nitrogen absorption–desorption isotherms. The monolith was used to separate lysozyme from chicken egg white in a short time with good resolution and reproducibility. The effects of pH and buffer concentration on elution have been investigated. In addition, the monolith was used to separate a mixture of proteins (bovine serum albumin, papain and lysozyme) and aromatic compounds with good resolution.

Investigation of temperature-responsivity and aqueous chromatographic characteristics of a thermo-responsive monolithic column

A thermo-responsive and macroporous monolithic cryogel was directly prepared by in situ free-radical redox cryo-polymerization in a stainless steel chromatographic column (100 mm × 4.6mm i.d.) using N-isopropylacrylamide (NIPAAm) as functional monomer and PEG-20,000 as porogen at -12°C. The internal morphology of resulting monolithic cryogel was estimated by scanning electron microscopy (SEM). Based on that, a submicron skeleton structure was observed. Besides, the gravimetrically determined rates of swelling/deswelling for thermo-responsive monolithic cryogel were much higher than that of hydrogel adopting the same component proportion via conventional method (25°C for 24h). Simultaneously, a temperature-dependent resolution of steroids was also achieved using only water as a mobile phase. The theoretical plate number of every analyte was more than 2000.

One-pot synthesis of ethylenediamine-connected graphene/carbon nanotube composite material for isolation of clenbuterol from pork

A fluffy porous ethylenediamine-connected graphene/carbon nanotube composite (EGC), prepared by a simple and time-saving one-pot synthesis, was successfully applied as an adsorbent in pipette-tip solid-phase extraction (PT-SPE) for the rapid extraction and determination of clenbuterol (CLB) from pork. In the one-pot synthesis, carbon nanotubes were inserted into graphene sheets and then connected with ethylenediamine through chemical modification to form a three-dimensional framework structure to prevent agglomeration of the graphene sheets. Under the optimum conditions for extraction and determination, good linearity was achieved for CLB in the range of 15.0-1000.0ngg-1 (r=0.9998) and the recoveries at three spiked levels were in the range of 92.2-96.2% with relative standard deviation ≤9.2% (n=3). In comparison with other adsorbents, including silica, NH2, C18, and Al2O3, EGC showed higher extraction and purification efficiency for CLB from pork samples. This analytical method combines excellent adsorption performance of EGC and high extraction efficiency of PT-SPE.

Property evaluations and application for separation of small molecules of a nanodiamond-polymer composite monolithic column.

A nanodiamond-polymer composite monolithic column was first prepared successfully with modified nanodiamond (ND) as monomer, ethylene glycol dimethacrylate (EDMA) as cross-linker, 1-dodecanol as porogenic agent and benzoyl peroxide/dimethylacetamide (BPO/DMA) as initiator at 35°C for 2.5h. There was a sharp increase of specific surface area with ND added about 22 times from 0mg (3.90m(2)/g) to 7mg (81.2m(2)/g) determined with BET. Characterizations including scanning electron microscopy (SEM), fourier-transform infrared spectra (FIRT) and mercury intrusion porosimetry (MIP) were used to determine the microstructure, group composition, pore size distribution (≃1.56μm) and porosity (≃0.7484μm) of the monolith. An excellent column stability was confirmed by permeability (1.258x10(-10)cm(2)) and good linearity (R(2)=0.998) corresponding to backpressures measured at different flow rates. The highest swelling ability of the composite was about (5%) and classical RPLC of the column obtained occurred with the acetonitrile concentration increasing from 20% to 85% in the mobile phase, above which another retention model of normal-phase chromatography appeared. The items of the eddy dispersion and the absorption-release kinetics were the decisional factors of the composite column compared with the factors of longitudinal diffusion, and the skeleton-eluent mass transfer resistance due to the finite diffusivity. Good separation of neutral and basic small molecules was obtained (24,350 plates/m for neutral molecules and 22,300 plates/m for basic ones) with the hydrophobicity retention mechanism, but not for the acidic ones except to regulate the pH of the mobile phase.

Preparation of a porous polymer monolithic column with an ionic liquid as a porogen and its applications for the separation of small molecules in high performance liquid chromatography

A novel porous polymer monolithic column was prepared by in situ free radical polymerization and used as a stationary phase for high performance liquid chromatography (HPLC). In this process, an ionic liquid (IL) was used as a porogen and reaction medium to create pores and enhance the flow-through properties of the polymer monoliths. The effect of IL in the polymerization mixture on the performance of the monoliths was studied in detail. The addition of IL can enhance the resolution and column efficiency compared to the monoliths with alcohol as the porogen. The chromatographic performance of the columns was demonstrated by the separation of various small molecules. The monolith exhibited a typical reversed phase chromatographic behavior with a column efficiency of 12 500 plates per m, which outperformed the commonly used porogen alcohol compounds. The results demonstrated that the IL was a potentially efficient porogen for the preparation of polymer monolithic columns. Moreover, the good mechanical stability, permeability, and reproducibility of column fabrication suggested that the proposed monolith can be expected to be an alternative tool for HPLC separation.