Hybrid Monolith Research Articles

Enantioseparation of basic chiral compounds on a clindamycin phosphate-silica/zirconia hybrid monolith by capillary electrochromatography

An organic–inorganic silica/zirconia hybrid monolithic capillary column was prepared by sol–gel process in a fused-silica capillary by using triethoxysilylpropylcarbamate (TEOSPC) derivative of clindamycin phosphate (CLIP) as a chiral selector. A sol solution consisting of 6×10−3M of polyethylene glycol, 1M of water, 2M of acetic acid and 0.04/0.96 ratio of CLIP-TEOSPC/Zr-Bu resulted in homogeneous monolith having well defined through-pores and tightly anchored to the capillary wall. The column was employed for capillary electrochromatographic enantioseparation of eight basic chiral drugs in mobile phases consisting of acetonitrile, methanol and ammonium acetate (AA, as the electrolyte). Effects of the compositions of solvents and electrolyte in the mobile phase, applied voltage and capillary temperature on chiral separation were investigated. The highest resolution values were obtained with mobile phases consisting of 40/60 MeOH/ACN and 100mM AA (for citalopram, Tröger's base, indapamide, metoprolol, cetirizine and atropine) and 35/65 MeOH/ACN and 100mM AA (for sertraline and propranolol) using −10kV applied voltage at 25°C.

One-pot preparation of glutathione–silica hybrid monolith for mixed-mode capillary liquid chromatography based on “thiol-ene” click chemistry

A novel glutathione (GSH)–silica hybrid monolithic column synthesized via a combination of thiol-ene click reaction and one-pot process was described, where thiol-end GSH organic monomer and 2,2-azobisisobutyronitrile (AIBN) were mixed with hydrolyzed tetramethyloxysilane (TMOS) and γ-methacryloxypropyltrimethoxysilane (γ-MAPS) and then introduced into a fused-silica capillary for simultaneous polycondensation and “thiol-ene” click reaction to form the GSH–silica hybrid monolith. The effects of the molar ratio of TMOS/γ-MAPS, the amount of GSH, and the volume of porogen on the morphology, permeability and pore properties of the prepared GSH–silica hybrid monoliths were studied in detail. A uniform monolithic network with high porosity was obtained. A series of test compounds including alkylbenzenes, amides, and anilines were used to evaluate the retention behaviors of the GSH–silica hybrid monolithic column. The results demonstrated that the prepared GSH–silica hybrid monolith exhibited multiple interactions including hydrophobicity, hydrophilicity, as well as cation exchange interaction. The run-to-run, column-to-column and batch-to-batch reproducibilities of the GSH–silica hybrid monolith for phenols’ retention were satisfactory with the relative standard deviations (RSDs) less than 1.3% (n=5), 2.6% (n=3) and 3.2% (n=3), respectively, indicating the effectiveness and practicability of the proposed method. In addition, the GSH–silica hybrid monolith was applied to the separation of nucleotides, peptides and protein tryptic digests, respectively. The successful applications suggested the potential of the GSH–silica hybrid monolith in complex sample analysis.

Fabrication of three-dimensional MoS2-graphene hybrid monoliths and their catalytic performance for hydrodesulfurization

A simple process to synthesize three-dimensional molybdenum disulfide-graphene monolithic catalysts (3D-MoS2-G) was developed. 3D-MoS2-G hybrid monoliths were fabricated by a combined hydrothermal self-assembly and freeze-drying treatment, in which ammonium tetrathiomolybdate and graphite oxide were used as starting materials. The structure and morphology of the samples were characterized by X-ray diffraction, Fourier transform infrared spectrometry, Raman spectrometry, field emission scanning electron microscopy, transmission electron microscopy and nitrogen adsorption. The catalytic performance of the hybrid monoliths was investigated by evaluating the activity for the hydrodesulfurization (HDS) of carbonyl sulfide (COS). In addition, the influence of microwave irradiation on the catalytic property of the 3D-MoS2-G monoliths was also investigated. It is demonstrated that after microwave irradiation the 3D-MoS2-G monoliths show an excellent activity for COS hydrogenation compared with the traditional MoS2/γ-Al2O3 catalyst prepared by impregnation-sulfidation. The 3D-MoS2-G-160 M monolith hydrothermally synthesized at 160 °C exhibits the highest COS conversion of 100% at a relatively low temperature (260 °C) for the HDS reaction. The superior performance of the 3D-MoS2-G-160 M catalyst can be ascribed to the unique hybridized structure of the MoS2 nanoparticles uniformly dispersed on graphene sheets in the monolith. [New Carbon Materials 2014, 29(2): 81–88]

PURIFICATION OF LUTEOLIN AND APIGENIN FROM CELERY LEAVES USING HYBRID ORGANIC–INORGANIC MONOLITHIC CARTRIDGE

□ A new type organic–inorganic hybrid monolithic cartridge (30×9.0mm, i.d.) was prepared and used as a solid-phase extraction (SPE) sorbent to purify luteolin and apigenin from celery leaves. The morphology of the monolithic material was evaluated by field emission-scanning electron microscopy and a Brunauer–Emmett–Teller test. A SPE-high performance liquid chromatography (HPLC) method was used to further test the performance of the hybrid monolithic cartridge. The HPLC analysis was performed on a C 18 column with acetonitrile/water (40:60, v/v) as the mobile phase and a flow rate of 0.5mL min −1 . Under the optimized conditions, good calibration curves were observed at seven luteolin and apigenin concentrations ranging from 1.0 to 100.0μ g mL −1 . The method recovery ranged from 93.0%to 102.6%, and the inter-day and intra-day relative standard deviations were less than 5%. These results suggest that this type of hybrid monolith can become an ideal adsorbent for the purification of bioactive compounds from natural plant extracts.

Synthesis, characterization and application of organic-inorganic hybrid and carbaryl-imprinted capillary monolithic column

Organic-inorganic hybrid and carbaryl-imprinted capillary monolith was synthesized via methacrylic acid(MAA) as functional monomer, γ-methacryloxypropyltrimethoxysilane(γ-MAPS) as crosslinker and carbaryl as template molecule in an acetonitrile/dichloromethane mixture(1:4, volume ratio). With the capillary column obtained from this monolith, three carbamates(carbaryl, fenobucarb and metolcarb) were separated effectively by electrochromatography with the kMIP/kNIP values of 7.57, 1.27 and 1.64, respectively. In 20 mmol/L phosphate buffer solution (pH=3.5) with 30% (volume fraction) of acetonitrile, carbaryl was separated directly from the three-carbamate mixture (carbaryl, fenobucarb and metolcarb) with an effective 15 cm-length imprinted column.

Preparation of polyhedral oligomeric silsesquioxane-based hybrid monolith by ring-opening polymerization and post-functionalization via thiol-ene click reaction

A polyhedral oligomeric silsesquioxane (POSS) hybrid monolith was simply prepared by using octaglycidyldimethylsilyl POSS (POSS-epoxy) and cystamine dihydrochloride as monomers via ring-opening polymerization. The effects of composition of prepolymerization solution and polycondensation temperature on the morphology and permeability of monolithic column were investigated in detail. The obtained POSS hybrid monolithic column showed 3D skeleton morphology and exhibited high column efficiency of ∼71,000 plates per meter in reversed-phase mechanism. Owing to this POSS hybrid monolith essentially possessing a great number of disulfide bonds, the monolith surface would expose thiol groups after reduction with dithiothreitol (DTT), which supplied active sites to functionalize with various alkene monomers via thiol-ene click reaction. The results indicated that the reduction with DTT could not destroy the 3D skeleton of hybrid monolith. Both stearyl methylacrylate (SMA) and benzyl methacrylate (BMA) were selected to functionalize the hybrid monolithic columns for reversed-phase liquid chromatography (RPLC), while [2-(methacryloyloxy)ethyl]-dimethyl-(3-sulfopropyl)-ammonium hydroxide (MSA) was used to modify the hybrid monolithic column in hydrophilic interaction chromatography (HILIC). These modified hybrid monolithic columns could be successfully applied for separation of small molecules with high efficiency. It is demonstrated that thiol-ene click reaction supplies a facile way to introduce various functional groups to the hybrid monolith possessing thiol groups. Furthermore, due to good permeability of the resulting hybrid monoliths, we also prepared long hybrid monolithic columns in narrow-bore capillaries. The highest column efficiency reached to ∼70,000 plates using a 1-m-long column of 75μm i.d. with a peak capacity of 147 for isocratic chromatography, indicating potential application in separation and analysis of complex biosamples.

Preparation of a hybrid organic-inorganic monolith for extraction and purification of quercetin and myricetin from Chamaecyparis obtusa

A new hybrid organic-inorganic monolithic cartridge was synthesized and used as the selective sorbent for the extraction and purification of quercetin and myricetin from Chamaecyparis obtusa via a solid-phase extraction method. The morphology of the monolithic material was examined by field emission-scanning electron microscopy and a Brunauer-Emmett-Teller(BET) test. The adsorption capacity of the obtained material for quercetin and myricetin was investigated by fitting the adsorption data to four different adsorption equations, of which the Langmuir-Freundlich isotherm was selected as the most suitable model. Under optimized conditions, good calibration curves were observed at nine concentrations ranged from 0.5 μg/mL to 100.0 μg/mL of quercetin and myricetin. The extraction recovery ranged from 74.5% to 84.6% and the inter- and intra-day relative standard deviations were <6%. This type of hybrid monolith has potential for the separation and purification of bioactive compounds from natural plant extracts.

Compressible Carbon Nanotube–Graphene Hybrid Aerogels with Superhydrophobicity and Superoleophilicity for Oil Sorption

Spilled oil represents a menace to the aquatic ecosystem and the whole environment in general and requires timely cleanup. Among all the avaliable technologies, oil sorption has attracted the most attention because of its simplicity and high level of effectiveness. The key for the development of this technology is convenient fabrication of high-performance oil sorbents that can be used repeatedly. In this work, a fast microwave irradiation-mediated approach has been proposed for manufacturing multiwall carbon nanotube (MWCNT)–graphene hybrid aerogels, in which MWCNTs are vertically anchored on the surface of cell walls of graphene aerogels. The hybrid monoliths show superhydrophobicity and superoleophilicity, a large pore volume, a large pore size, and excellent compressibility, demonstrating outstanding performance for recyclable oil sorption.

Synthesis and Evaluation Methacrylate-Based Monolithic Materials Mixed with Carbon Nanotubes

An effective approach to synthesize methacrylate-based hybrid monoliths was carried out by photopolymerization and the properties of the obtained monoliths mixed with mult-wall carbon nanotube (MWNT) were studied in this paper. The prepared hybrid materials with MWNT in the range of 0-5% total weight of monomers were characterized by Fourier transform infrared spectra, thermo-gravimetric analysis (TGA), and mercury intrusion porosimetry, respectively. Moreover, their porosities were evaluated by the determination of flow rate for different prepared monolithic capillaries. The results showed that the monoliths with more MWNT (1-5%) possessed larger pore sizes between 1-10 μm. The hybrid monoliths have the potential advantages including stronger hydrophobic properties and less resistance for the application of reversed phase liquid chromatography in the micro-column separation.

A novel imidazolium-based organic–silica hybrid monolith for per aqueous capillary electrochromatography

A new imidazolium-based organic–silica hybrid monolith by binding the imidazole-1-acetic acid onto the surface of monolithic silica was prepared through a simple route. The obtained monolith exhibited per aqueous capillary electrochromatography (PACEC) characteristics in water-rich mobile phases. A typical per aqueous chromatography behavior was observed for the test solutes (an increase in H2O content resulted in an increase in retention). The effects of water content, pH and ion strength of mobile phase on the retention of test compounds in highly aqueous eluents were investigated in detail. PACEC in itself is a green chromatography mode that makes green capillary electrochromatography possible. Various hydrophilic compounds including amino acids were baseline separated with enhanced resolution of the obtained monolith under PACEC mode. It is evidenced that solutes were retained predominantly by hydrophobic interactions under PACEC conditions. Therefore, PACEC has the potential to replace hydrophilic interaction chromatography and meanwhile it is complementary to the reverse-phase chromatography.

Three-dimensional superhydrophobic porous hybrid monoliths for effective removal of oil droplets from the surface of water

An effective, facile approach is reported for constructing three-dimensional (3D) superhydrophobic porous hybrid monoliths by a reduced self-assembly procedure using a graphene oxide (GO) and polystyrene (PS) solution with L-ascorbic acid. Water contact angle (CA) measurements demonstrate that the entire body of the reduced graphene oxide/PS (rGO/PS) monolith is superhydrophobic, with a water CA of 156° for the surface and 152° for the cross-section. A nitrogen adsorption–desorption analysis reveals that there are a large number of pores (153.9 m2 g−1, BET) in the monoliths. The superhydrophobic porous hybrid monoliths exhibit a remarkable capability to adsorb a wide range of organic solvents and oil droplets from the surface of water. Furthermore, the highly water repellent character of the monoliths is still kept even under severe conditions (e.g. acidic, basic and saline). Such expedient and low-cost superhydrophobic porous monoliths have a lot of promising potential applications, including self-cleaning, anti-corrosion, anti-sticking, water remediation and oil spillage cleanup.

Photoinduced thiol-ene polymerization reaction for fast preparation of macroporous hybrid monoliths and their application in capillary liquid chromatography.

Hybrid monoliths with a macroporous structure were prepared within a few minutes via a photoinduced thiol-ene polymerization reaction, the surfaces of which showed hydrophobic character. The monolithic column demonstrated good separation performance towards alkylbenzenes, peptides, proteins and BSA tryptic digest in cLC.

Effect of dexamethasone on proteomics of endometrial fluid from mares susceptible to endometritis

A sulfonate–silica hybrid strong cation-exchange (SCX) monolith was synthesized at the proximal end of a capillary zone electrophoresis column and used for on-line solid-phase extraction (SPE) sample preconcentration. Sample was prepared in an acidic buffer and deposited onto the SCX-SPE monolith and eluted using a basic buffer. Electrophoresis was performed in an acidic buffer. This combination of buffers results in formation of a dynamic pH junction, which allows use of relatively large elution buffer volume while maintaining peak efficiency and resolution. All experiments were performed with a 50 µm ID capillary, a 1 cm long SCX-SPE monolith, a 60 cm long separation capillary, and a electrokinetically pumped nanospray interface. The volume of the capillary is 1.1 µL. By loading 21 µL of a 1×10−7 M angiotensin II solution, an enrichment factor of 3000 compared to standard electrokinetic injection was achieved on this platform while retaining efficient electrophoretic performance (N=44,000 plates). The loading capacity of the sulfonate SCX hybrid monolith was determined to be ~15 pmol by frontal analysis with 10−5 M angiotensin II. The system was also applied to the analysis of a 10−4 mg/mL bovine serum albumin tryptic digest; the protein coverage was 12% and 11 peptides were identified. Finally, by loading 5.5 µL of a 10−3 mg/mL E. coli digest, 109 proteins and 271 peptides were identified in a 20 min separation; the median separation efficiency generated by these peptides was 25,000 theoretical plates.

Sol-Gel Synthesis of Novel Silica Hybrid Xerogels: Porous Studies

Hybrid silica xerogel mesoporous composite was synthesized by a low temperature acid catalysed sol-gel route where a natural copolymer; sodium alginate (Na-COOH) together with calcium oxide (CaO) powder were incorporated into silica sol precursor prior to gel formation. For this study, bulk xerogels samples were prepared with the amount of silica precursor and the natural copolymer was fixed meanwhile the loading of calcium oxide was varied at 10 and 20 wt%. The porous properties were studied and the comparison between the hybrid silica and monolith was made. The calcium oxide powder used in this study was prepared from calcium hydroxide, CaOH compound, which been calcined at 1000°C for 3 hours in normal air. Mesoporous structure with small particle size and glassy phase of matrixes are the main features of the prepared xerogels. The presence of sodium alginate and calcium oxide in silica matrixes produces a significant decrease especially in total surface area and porosity volume of the xerogel samples. Monolith silica xerogels exhibits a very large surface area approximately at 600 m2/g compared to the hybrid xerogels which showed 120m2/g and 25m2/g for the respective 10 and 20 wt.% of calcium oxide loading. Nevertheless, only a slight increased in pore size has been observed due to the increased amount of calcium oxide loading.

Dipyridyl‐immobilized ionic liquid type hybrid silica monolith for hydrophilic interaction electrochromatography

A pyridinium-based immobilized ionic liquid type multifunctional hybrid silica monolith was prepared by the in situ polymerization of 3-chloropropyl-silica matrix and 4,4'-dipyridyl for hydrophilic interaction CEC. The obtained hybrid monolith possessed of high stable skeletal microstructures with obviously hydrophilic retention mechanism under ACN content >50% in the mobile phase. Strong and stable anodic EOF could be observed under a broad pH range from pH 3.0 to 9.0. Due to the immobilized dipyridyl groups bonded to the silica matrix surface, the resulting hydrophilic hybrid monolith possessed multiple separation interactions including hydrogen bond, π-π, and anion exchange. Excellent separations of various polar analytes including electroneutral phenols, charged acid nucleotides, and basic analytes were successfully achieved. The highest column efficiencies up to 120,000, 164,000, and 106,000 plates/m were obtained for nucleotides, nucleic acid bases, and nucleosides and nicotines, respectively. These results demonstrated that the dipyridyl-immobilized ionic liquid functionalized hybrid monolith possessed highly mechanical stability and good chromatographic performance for hydrophilic interaction electrochromatography.

Preparation of polyhedral oligomeric silsesquioxane based hybrid monoliths by ring‐opening polymerization for capillary LC and CEC

A new organic-inorganic hybrid monolith was prepared by the ring-opening polymerization of octaglycidyldimethylsilyl polyhedral oligomeric silsesquioxane (POSS) with 1,4-butanediamine (BDA) using 1-propanol, 1,4-butanediol, and PEG 10,000 as a porogenic system. Benefiting from the moderate phase separation process, the resulting poly(POSS-co-BDA) hybrid monolith possessed a uniform microstructure and exhibited excellent performance in chromatographic applications. Neutral, acidic, and basic compounds were successfully separated on the hybrid monolith in capillary LC (cLC), and high column efficiencies were achieved in all of the separations. In addition, as the amino groups could generate a strong EOF, the hybrid monolith was also applied in CEC for the separation of neutral and polar compounds, and a satisfactory performance was obtained. These results demonstrate that the poly(POSS-co-BDA) hybrid monolith is a good separation media in chromatographic separations of various types of compounds by both cLC and CEC.

Thiol-Containing Polysilsesquioxane Liquid and Photocurable Sulfur-Containing Transparent Organic–Inorganic Hybrid Monoliths Obtained via Cosolvent-Free Hydrolytic Polycondensation

Abstract Cosolvent-free hydrolytic polycondensation of trimethoxy(3-sulfanylpropyl)silane under acidic conditions was found to yield thiol-containing polysilsesquioxane (PSQ) liquid. The resultant PSQ liquid is stable at room temperature and serves as a precursor of sulfur-containing transparent organic–inorganic hybrid monoliths prepared via ultraviolet (UV) photoinduced thiol–ene reaction. The factors that determine the UV transparency of the hybrids were investigated. Sulfur-containing organic–inorganic hybrids showing good transparency in the UV spectral region are obtained using a vinyl compound, which is transparent around the UV absorption edge of thiol groups.

A novel organic–inorganic hybrid monolithic column prepared in-situ in a microchip and its application for the determination of 2-amino-4-chlorophenol in chlorzoxazone tablets

γ-Alumina nanoparticles (γ-Al2O3) were introduced to the conventional poly(methacrylic acid-co-ethylene glycol dimethacrylate) (MAA-co-EGDMA) monolith to prepare a novel organic-inorganic hybrid monolith, poly(MAA-co-EGDMA)-Al2O3 monolith. The polymerization was induced in-situ with UV irradiation in an ultraviolet transparent polymethyl methacrylate (PMMA) microfluidic chip. The monolith-based solid phase microextraction system was used for the on-line determination of 2-amino-4-chlorophenol (ACP) in chlorzoxazone tablets coupled with an optical fiber spectrophotometer. Several parameters affecting the adsorption/desorption, including sample pH value, sample flow rate, sampling time, eluent flow rate, and eluting time, were investigated in detail. Under the optimized conditions, limit of detection (LOD) and limit of quantification (LOQ) of the method were calculated to be 2.8 and 9.1µgL−1, respectively, with the relative standard deviation (RSD) of 3.1%.

Improved sulfoalkylbetaine‐based organic‐silica hybrid monolith for high efficient hydrophilic interaction liquid chromatography of polar compounds

A novel sulfoalkylbetaine-based zwitterionic organic-silica hybrid monolith was synthesized by using 3-dimethyl-(3-(N-methacrylamido) propyl) ammonium propane sulfonate (DMMPPS, neutral sulfoalkyl-betaine monomer). The added amount of zwitterionic monomer was significantly increased when DMMPPS was used instead of the conventionally used acidic sulfoalkyl-betaine monomer, that is, the N,N-dimethyl-N-methacryloxyethyl-N-(3-sulfopropyl) ammonium betaine, and this led to a significantly improved hydrophilicity of the monolith. The DMMPPS-based organic-silica hybridmonolith exhibited good mechanical stability and excellent separation performance. About ∼20 mμ plate height (corresponding to column efficiency of ∼50,000 plates/m) was obtained for nucleoside at the linear velocity of 1 mm/s. The proposed monolithic column was successfully applied to separate purines/pyrimidines, nucleotides, and tryptic digest of bovine hemoglobin in a nano-HILIC mode, and the results demonstrated that such monolith has the potential for separation of a variety of hydrophilic substances.

Preparation of a polyhedral oligomeric silsesquioxane-based perfluorinated monolithic column

A monolithic column with high affinity to fluorous compounds was prepared using a polyhedral oligomeric silsesquioxane (POSS) reagent as the cross-linker and pentadecafluorooctyl methacrylate (PDFOMA) as the functionality monomer. The pore properties and permeability could be tuned by the composition of the polymerization mixture. The characterization and evaluation results revealed that the obtained POSS–PDFOMA hybrid monolith owned the merits of POSS and PDFOMA with good mechanical stability, no residual silanol and high affinity to fluorous compounds. A series of perfluoroalkyl methacrylates were baseline resolved on the optimized monolithic column under isocratic elution of 70% acetonitrile aqueous solution. Such a resolution could not be achieved on a silica-based C18 monolithic column. A column efficiency of 30000N/m was observed. In addition, several perfluoroalkyl sulfonates were also baseline separated on the fluorous monolith applying 0.1% (v/v) acetic acid aqueous solution containing 75% acetonitrile as mobile phase without the addition of ammonium.