Hybrid Monolithic Column Research Articles

Incorporation of metal-organic framework amino-modified MIL-101 into glycidyl methacrylate monoliths for nano LC separation.

Metal-organic frameworks consisting of amino-modified MIL-101(M: Cr, Al, and Fe) crystals have been synthesized and subsequently incorporated to glycidyl methacrylate monoliths to develop novel stationary phases for nano-liquid chromatography. Two incorporation approaches of these materials in monoliths were explored. The metal-organic framework materials were firstly attached to the pore surface through reaction of epoxy groups present in the parent glycidyl methacrylate-based monolith. Alternatively, NH2 -MIL-101(M) were admixed in the polymerization mixture. Using short time UV-initiated polymerization, monolithic beds with homogenously dispersed metal-organic frameworks were obtained. The chromatographic performance of embedded UV-initiated composites was demonstrated with separations of polycyclic aromatic hydrocarbons and non-steroidal anti-inflammatory drugs as test solutes. In particular, the incorporation of the NH2 -MIL-101(Al) into the organic polymer monoliths led to an increase in the retention of all the analytes compared to the parent monolith. The hybrid monolithic columns also exhibited satisfactory run-to-run and column-to-column reproducibility.

Preparation of restricted-access material precolumns by grafting δ-gluconolactone onto a hybrid silica monolithic column for on-line solid-phase extraction of tetracycline residues from milk.

A restricted-access material-hybrid monolithic column was prepared based on single-component organosiloxane and dynamic grafting of δ-gluconolactone for on-line solid phase extraction of tetracycline antibiotic residues from milk. The hybrid monolithic column was prepared in a stainless-steel chromatographic column using methyltrimethoxysilane as the single precursor. δ-Gluconolactone was covalently coupled to aminopropyl derivatized hybrid monolithic column, which formed hydrophilic structures on the surface of the pore of the restricted-access material-hybrid monolithic column. The columns were characterized by scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, nitrogen adsorption, contact angle analysis, dynamic adsorption, and chromatographic performance evaluation. The restricted-access material-hybrid monolithic column was applied to the on-line extraction of tetracycline residues from milk. An enrichment factor of 15.8 and a good sample clean-up effect were obtained under the optimized conditions. The recoveries of the three spiked milk samples were between 81.7 and 102.5% with relative standard deviations (n=3) in the range of 2-5%. The limits of detection (S/N=3) for target compounds were in the range of 3.80-9.03μg/kg. The results show that the on-line extraction using the restricted-access material-hybrid monolithic column was powerful for food sample pretreatment with high selectivity and good clean-up effect.

Synthesis of Hybrid Monolithic Columns Using a Click Chemistry Reaction for Application in Capillary Liquid Chromatography

Hybrid monolithic columns present characteristics of both silica and organic monoliths, such as good mechanical properties, wide pH tolerance, high permeability and stability and little swelling or shrinkage. A common way to prepare this type of material is by using alkoxysilanes and organic monomers via the sol-gel process and click chemistry reactions. In this paper, a co-condensation organic-silica hybrid monolith was prepared based on tetramethoxysilane (TMOS) and vinyltrimethoxysilane (VTMS) as precursors for the sol-gel process. The hybrid monolithic matrix was modified with dodecanethiol through the thiol-ene click chemistry reaction and the resulting material was compared with a dodecanesilane bonded phase column, in order to evaluate the differences in the chromatographic performance of a stationary phase prepared by a classic reaction or by a thiol-ene click reaction. Additionally, the stability of the thiol-ene column over time was evaluated. The effects of different synthetic proportions were investigated in detail by scanning electron microscopy (SEM), scanning capacitively coupled contactless conductivity detection (sC4D), Fourier-transform infrared spectroscopy (FTIR) and retention behavior in capillary liquid chromatography (cLC). The hybrid monolithic column prepared with dodecanethiol was the best one for the separation of alkylbenzenes and polycyclic aromatic hydrocarbons by cLC-UV.

Simultaneous speciation analysis of chromium and antimony by novel carboxyl-functionalized hybrid monolithic column solid phase microextraction coupled with ICP-MS

Carboxyl hybrid monolithic columns were prepared from simple silane agents by one-pot for simultaneous speciation analysis of chromium and antimony.

Monolithic Material Prepared with Nanodiamond as Monomer for the Enrichment of β-Sitosterol in Edible Oil

In this paper, a hybrid monolithic column with modified nanodiamond and 1-dodecene as co-monomers was prepared and applied to the online enrichment and purification of β-sitosterol in edible oil. The obtained monolithic column was characterized by scanning electron microscopy (SEM) and nitrogen adsorption–desorption isotherm measurement, which indicated that the monolith possessed characteristics of porous structure and high permeability. Under the optimum conditions for extraction and determination, the linear regression coefficient for β-sitosterol was 0.998; the limit of detection (LOD) and the limit of quantitation (LOQ) were 3.0 μg mL−1 and 10.0 μg mL−1, respectively; the relative standard deviation (RSD) of intra-day and inter-day assays for four edible oils were 2.33–6.58% and 3.24–6.94%, respectively. The recovery was in the range of 89.6–105.5%. The results showed that the hybrid monolithic column with high selectivity and good permeability were successfully used as online solid-phase extraction (SPE) column for determination of β-sitosterol in edible oil.

Preparation of thiol- and amine-bifunctionalized hybrid monolithic column via “one-pot” and applications in speciation of inorganic arsenic

A thiol- and amine-bifunctionalized organic-inorganic hybrid monolithic column was prepared for the first time via one-pot co-condensation of 3-mercaptopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane and tetraethylorthosilicate, and utilized for separation and enrichment of inorganic arsenic species. Various parameters of solid phase microextraction (SPME) operation and analytical performance were also investigated systematically. Under the optimum condition, both As(III) and As(V) can be adsorbed over a wide pH range (3.0–8.0) and eluted in turn, in which 3% HNO3 (v/v) was firstly used to selectively release As(V), and then 3% HNO3 with 0.01 mol L−1 KIO3 or 15% mercaptosuccinic acid (MSA) (m/v) to selectively release As(III). Meanwhile, the elution mechanism of As(III) and As(V) was elucidated comprehensively, and notably, the novel eluent, HNO3 + MSA, was recommended for eluting As(III). Therefore, the thiol- and amine-bifunctionalized organic-inorganic hybrid monolithic column as an ideal SPME matrix for the speciation analysis of arsenic in environmental waters has the merits of facile preparation, low cost, high adsorption capacity and selective desorption. In addition, compared with thiol- and amine-bifunctionalized mesoporous silica, the bifunctional hybrid monolith based SPME protocol with less time and reagent consumption is promising to be applied not only to filed sampling but also to on-line analysis.

Preparation of an acryloyl β-cyclodextrin-silica hybrid monolithic column and its application in pipette tip solid-phase extraction and HPLC analysis of methyl parathion and fenthion.

An acryloyl β-cyclodextrin-silica hybrid monolithic column for pipette tip solid-phase extraction and high-performance liquid chromatography determination of methyl parathion and fenthion has been prepared through a sol-gel polymerization method. The synthesis conditions, including the volume of cross-linker and the ratio of inorganic solution to organic solution, were optimized. The prepared monolithic column was characterized by thermogravimetric analysis, scanning electron microscopy, and Fourier transform infrared spectroscopy. The eluent type, volume and flow rate, sample volume, flow rate, acidity, and ionic strength were optimized in detail. Under the optimized conditions, a simple and sensitive pipette tip solid-phase extraction with high-performance liquid chromatography method was developed for the determination of methyl parathion and fenthion in lettuce. The method yielded a linear calibration curve in the concentration ranges of 15-400μg/kg for methyl parathion and 20-400μg/kg for fenthion with correlation coefficients of above 0.9957. The limits of detection were 4.5μg/kg for methyl parathion and 6.0μg/kg for fenthion, respectively. The recoveries of methyl parathion and fenthion spiked in lettuce ranged from 96.0 to 104.2% with relative standard deviations less than 8.4%.

Amino acid and ionic liquid modified polyhedral oligomeric silsesquioxane-based hybrid monolithic column for high-efficiency capillary liquid chromatography

In this study, a novel amino acid and ionic liquid dual organically functionalized reagents modified polyhedral oligomeric silsesquioxane methacryl substituted (POSS-MA) based hybrid monolithic column (POSS-VBI-Cys) was designed and reported. With amino acid L-cysteine and ionic liquid 1-vinyl-3-butylimidazolium bromide as dual monomers, POSS-MA as the crosslinker, the new POSS-VBI-Cys hybrid monolithic column could be facilely fabricated via the “one-pot” free radical copolymerization and thiol-ene click reaction. Because of the introduction of polar amino acid L-cysteine, the new POSS-VBI-Cys column exhibited attenuated hydrophobicity in reversed-phase liquid chromatography separation. Polar amides, nucleosides and nucleic acid bases displayed strong retention on the POSS-VBI-Cys column and could be successfully separated. Furthermore, the new POSS-VBI-Cys column displayed good separation selectivity for model glycoproteins and non-glycoproteins mixture and it was also successfully used for the purification and separation of TARG1 protein from its originally expressed sample. In the future research, we will further exploit its performances for separation of intact proteins and in-depth proteome applications.

Effect of carbon nanohorns in the radical polymerization of methacrylate monolithic capillary columns and their application as extractant phases

A successful copolymerization of the single-walled carbon nanohorns (SWNHs) with methacrylate monomers was achieved via thermal initiated free-radical polymerization because of the high reactivity of the SWNHs in comparison with other carbon nanostructures. The hybrid solids were deeply characterized in terms of morphology, by scanning electron microscopy (SEM). The effect of the incorporation of the bare or oxidized (o-SWNHs) carbon nanoparticles at different percentages (0–0.5 wt%) in polymerization mixtures to obtain hybrid monolithic capillary columns has been evaluated. In addition, their impact both in the polymerization step and in the extraction capacity was deeply studied. Final hybrid monoliths were applied for the extraction of polycyclic aromatic hydrocarbons and nonsteroidal anti-inflammatory drugs in water and biological samples, respectively. The precision was calculated both intra- and inter-capillaries obtaining satisfactory RSD values of less than 19.1%, which indicated the high robust reproducibility of the extraction procedure and the synthesis method. The accuracy of the method was also evaluated through a recovery study giving good recovery values, which varied between 78% and 112% for PAHs in waters, and 90–114% for NSAIDs in human urine samples.

Preparation and analytical application of novel thiol-functionalized solid extraction matrices: From mesoporous silica to hybrid monolithic capillary column

A comprehensively comparative study of thiol-functionalized mesoporous silica and organic-inorganic hybrid monolithic column was reported, aiming at the separation and enrichment of inorganic arsenic. Thiol-functionalized mesoporous silica was synthesized based on the one-step co-condensation method. At the same time, a novel thiol-functionalized organic-inorganic hybrid monolithic column was synthesized using an unconventional ternary weak basic solvent system via one-step sol-gel process. The approach to prepare monolithic column through mild condition remarkably improved delamination phenomenon of thiol-functionalized hybrid monolithic column easily caused by conventional methods. As(III) can be selectively uptaken by the hybrid monolithic column and homemade syringe-based solid phase extraction device containing mesoporous silica through chelation in a wide range of pH, while As(V) cannot, and then the captured As(III) was eluted by 3% HNO3 (v/v) with 0.01 mol L−1 KIO3. Under the optimized conditions, the extraction recoveries were 91–102% and 93–103% for mesoporous silica and monolithic column, respectively. Although both two materials were ideal solid matrices for the removal and speciation analysis of As(III) in environmental waters, the monolith-based solid phase microextration protocol was more fast and reagent-saving than the other, which endued monolithic columns with more application prospects for trace elemental analysis and speciation. Even so, the exploration of mesoporous silica could efficiently pilot the synthesis of monolithic columns.

Thiol-radical-mediated polymerization for preparation of POSS-containing polyacrylate monoliths in capillary liquid chromatography

Through introducing octakis (3-mercaptopropyl) octasilsesquioxane (POSS-SH) synthesized in our lab to the prepolymerization solution containing stearyl acrylate (SA), 1,6-hexanediol ethoxylate diacrylate (HEDA) in the existence of porogenic solvents (tetrahydrofuran, 1,4-butanediol and 1-propanol), a POSS-containing hybrid monolithic column was fabricated via photo-initiated thiol-acrylate polymerization within 7 min. The resulting poly(SA-co-HEDA-co-POSS) monoliths were investigated by physical characterization and chromatographic evaluation. It was found that both the additive amount of thiol group and the proportion of porogenic solvents played vital effect on column efficiency, pore morphology and hydrophobicity of monolithic columns. Consequently, the poly(SA-co-HEDA-co-POSS) monolith possessed superior thermal stability, suitable permeability and homogeneous microstructure. The highest column efficiency was ∼111,000 N m−1 for butylbenzene at the linear velocity of 0.71 mm s−1 in reversed-phase liquid chromatography. Subsequently, baseline separations of 9 phenolic compounds, 5 anilines and 5 antibiotics were achieved, indicating the monolithic poly(SA-co-HEDA-co-POSS) column had great ability for separation of small molecules. The analytic results of the tryptic digest of BSA and HeLa were also proved that the hybrid monolith had potential for the analysis of complicated biological samples.

Preparation of attapulgite nanoparticles-based hybrid monolithic column with covalent bond for hydrophilic interaction liquid chromatography

In current study, an attapulgite nanoparticles-based hybrid monolith was prepared by crosslinking 3-trimethoxysilylpropyl methacrylate modified attapulgite nanoparticles with acrylamide and N, N′-methylenebisacrylamide. The crosslinking of attapulgite into the hybrid monolithic matrix has notable increased the column efficiency of adenosine comparing with the neat one without attapulgite. The resulting hybrid monoliths showed good permeability and good mechanical stability. It was further applied for separation of polar compounds by hydrophilic interaction chromatography (HILIC). The key factors affecting the separation efficiency of the developed hybrid monoliths (i.e. acetonitrile content, salt concentration and pH in the mobile phase) have been completely investigated. The column efficiency was up to 147,613 plates/m for the HILIC separation of aspirin. Good repeatability of retention time was achieved, with relative standard deviations for run-to-run (n = 3), column-to-column (n = 3) and batch-to-batch (n = 3) in the range of 1.08–1.45%, 2.44–3.41% and 2.15–4.96%, respectively. We propose that the attapulgite nanoparticles-based hybrid monolith would provide a promising stationary phase for hydrophilic interaction chromatography.

One-pot preparation of an acryloyled β-cyclodextrin-silica hybrid monolithic column and its application for determination of carbendazim and carbaryl

This work describes, for the first time, an acryloyled β-cyclodextrin hybrid monolith column was synthesized, under aqueous-phase conditions, and used for solid-phase microextraction of carbendazim and carbaryl. The monolithic column was characterized using scanning electron microscopy, nitrogen adsorption–desorption, thermogravimetric analysis and Fourier transform infrared spectroscopy, and used as the adsorbent for solid phase microextraction (SPME) of carbendazim and carbaryl. After optimization of the SPME conditions, a simple and sensitive SPME-HPLC method was developed for the determination of carbendazim and carbaryl in leafy vegetables. The method exhibited a good liner response in the range 5–400 μg/kg (R2 = 0.9994) for carbendazim and 10–400 μg/kg (R2 = 0.9996) for carbaryl, respectively. The limits of detection were 1.0 and 1.5 μg/kg for carbendazim and carbaryl, respectively, in leafy vegetables. Recoveries ranged from 92.6% to 110.1%, and the relative standard deviations were less than 6.1%.

Ultrafast preparation of a polyhedral oligomeric silsesquioxane-based ionic liquid hybrid monolith via photoinitiated polymerization, and its application to capillary electrochromatography of aromatic compounds.

An ionic liquid hybrid monolithic capillary column was prepared within 7min via photoinitiated free-radical polymerization of an ionic liquid monomer (1-butyl-3-vinylimidazolium-bis[(trifluoromethyl)sulfonyl]imide); VBIMNTF2) and a methacryl substituted polyhedral oligomeric silsesquioxane (POSS-MA) acting as a cross-linker. The effects of composition of prepolymerization solution and initiation time on the porous structure and electroosmotic flow (EOF) of monolithic column were investigated. The hybrid monolith was characterized by scanning electron microscopy and FTIR. Owing to the introduction of a rigid nanosized POSS silica core and ionic liquids with multiple interaction sites, the monolithic column has a well-defined 3D skeleton morphology, good mechanical stability, and a stable anodic electroosmotic flow. The hybrid monolithic stationary phase was applied to the capillary electrochromatographic separation of various alkylbenzenes, phenols, anilines and polycyclic aromatic hydrocarbons (PAHs). The column efficiency is highest (98,000 plates/m) in case of alkylbenzenes. Mixed-mode retention mechanisms including hydrophobic interactions, π-π stacking, electrostatic interaction and electrophoretic mobility can be observed. This indicates the potential of this material in terms of efficient separation of analytes of different structural type. Graphical Abstract Preparation of a mixed-mode ionic liquid hybrid monolithic column via photoinitiated polymerization of methacryl substituted polyhedral oligomeric silsesquioxane (POSS-MA) and 1-butyl-3-vinylimidazolium-bis[(trifluoromethyl)sulfonyl]imide (VBIMNTF2) ionic liquid for use in capillary electrochromatography.

A hybrid monolithic column based on layered double hydroxide-alginate hydrogel for selective solid phase extraction of lead ions in food and water samples

In order to develop an accurate and precise determination method based on solid phase extraction of Pb(II) in food and water samples, a hybrid monolithic column based on layered double hydroxides (LDHs) nanosheets-alginate hydrogel has been synthesized. Combining the advantages of porous 3D framework of hydrogel with selective adsorption of LDHs toward Pb(II), the hydrogel-based hybrid monolithic column shows enhanced enrichment selectivity and efficiency for target ions. Effects of hydrogel composition, pH, concentration and type of eluent, sample volume, and interfering ions on the recoveries of the analytes were also investigated. Under the optimal experiment conditions of method, the limit of detection, preconcentration factor and precision as RSD% are found to be 0.39 μg L−1, 53.7 and 2.65%, respectively. Trace Pb(II) can be quantitatively preconcentrated at pH 6.0 with recoveries >97%. Finally, the method was successfully verified by analyzing spiked Pb2+ in water and drinking samples.

Fast preparation of hybrid monolithic columns via photo-initiated thiol-yne polymerization for capillary liquid chromatography

Although several approaches have been developed to fabricate hybrid monoliths, it would still take a few hours to finish the formation of monoliths. Herein, photo-initiated thiol-yne polymerization was first adopted to in situ fabricate hybrid monoliths within the confines of UV-transparent fused-silica capillary. A silicon-containing diyne (1,3-diethynyltetramethyl-disiloxane, DYDS) was copolymerized with three multithiols, 1,6-hexanedithiol, trimethylolpropane tris(3-mercaptopropionate) and pentaerythriol tetrakis(3-mercaptopropionate), by using a binary porogenic system of diethylene glycol diethyl ether (DEGDE)/poly(ethylene glycol) (PEG200) within 10 min. Several characterizations of three hybrid monoliths (assigned as I, II and III, respectively) were performed. The results showed that these hybrid monoliths possessed bicontinuous porous structure, which was remarkably different from that via typical free-radical polymerization. The highest column efficiency of 76,000 plates per meter for butylbenzene was obtained on the column I in reversed-phase liquid chromatography (RPLC). It was observed that the efficiencies for strong-retained butylbenzene were almost close to those of weak-retained benzene, indicating a retention-independent efficient performance of small molecules on hybrid column I. The surface area of this hybrid monolith was very small in the dry state (less than 10.0 m2/g), and the chromatographic behavior of hybrid monolithic columns would be possibly explained by radical-mediated step-growth process of thiol-yne polymerization. Finally, the column I was applied for separation of BSA tryptic digest by cLC–MS/MS, indicating satisfactory separation ability for complicated samples.

Synthesis of boronate-functionalized organic-inorganic hybrid monolithic column for the separation of cis-diol containing compounds at low pH.

In this work, an organic-inorganic hybrid boronate affinity monolithic column was prepared via "one-pot" process using 4-vinylphenylboronic acid as organic monomer and divinylbenzene as cross-linker. The effects of reaction temperature, solvents and composition of organic monomers on the column properties (e.g. morphology, permeability, and mechanical stability) were investigated. A series of test compounds including small neutral molecules, aromatic amines, and cis-diol compounds were used to evaluate the retention behaviors of the prepared hybrid monolithic column. The results demonstrated that the prepared hybrid monolith exhibited mixed-interactions including hydrophilicity, cation exchange, and boronate affinity interaction. The run-to-run, day-to-day and batch-to-batch reproducibilities of the prepared hybrid monolith for thiourea's retention time were satisfactory with the relative standard deviations (RSDs) less than 0.09, 1.45 and 4.05% (n=3), respectively, indicating the effectiveness and practicability of the proposed method.

Preparation of a long-alkyl-chain-based hybrid monolithic column with mixed-mode interactions using a "one-pot" process for pressurized capillary electrochromatography.

A simple "one-pot" approach for the preparation of a new vinyl-functionalized organic-inorganic hybrid monolithic column is described. In this improved method, the hydrolyzed alkoxysilanes of tetramethoxysilane and triethoxyvinylsilane were used as precursors for the synthesis of a silica-based monolith, while 1-hexadecene and sodium ethylenesulfonate were used as vinyl functional monomers along with azobisisobutyronitrile as an initiator. The effects of reaction temperature, urea content, and composition of organic monomers on the column properties (e.g. morphology, mechanical stability, and chromatographic performance) were investigated. The monolithic column was used for the separation of neutral solutes by reversed-phase pressurized capillary. Furthermore, the monolith can separate various aromatic amines, which indicated its excellent cation-exchange capability and hydrophobic interactions. The baseline separation of the aromatic amines was obtained with a column efficiency of up to 78000 plates/m.

Green synthesis of monolithic column incorporated with graphene oxide using room temperature ionic liquid and eutectic solvents for capillary electrochromatography

In this work, a hybrid monolith incorporated with graphene oxide (GO) was prepared in the first time with binary green porogens of deep eutectic solvents (DESs) and room temperature ionic liquids (RTILs). GO was modified with 3-(trimethoxysilyl) propylmethacrylate (γ-MPS), and the resultant GO-MPS can be incorporated into poly (methacrylic acid-co-butylmethacrylate-co-ethylene glycol dimethacrylate) monoliths covalently. A hybrid monolithic column with high permeability and homogeneity can be achieved due to good dispersion of GO-MPS in the green solvents. The GO-MPS incorporated monolith was characterized by transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis and nitrogen adsorption tests. The separation of small organic molecules of alkylphenones and alkylbenzenes was used to evaluate the performance of GO-MPS grafted monolith. The GO-MPS grafted monolith displayed the maximum column efficiency of 147,000 plates/m, about twice higher than the GO-free monolith. In addition, all of the retention and selectivity of small molecules of alkylphenones and alkylbenzenes increased due to the addition of GO-MPS. The results demonstrated that the use of DESs and RTILs is a powerful approach for the preparation of GO incorporated polymer monoliths. The monolith was further applied to the separation of tryptic digests from bovine serum albumin, and the result indicated its potential in the analysis of some complex samples.

Evaluation of the Effect of Plant Growth Promoting Endophytic Bacteria from Pinellia ternata Using an Efficient Organic Silica Hybrid Monolithic Column

Evaluation of the Effect of Plant Growth Promoting Endophytic Bacteria from <i>Pinellia ternata </i> Using an Efficient Organic Silica Hybrid Monolithic Column