"One-pot" process for fabrication of organic-silica hybrid monolithic capillary columns using organic monomer and alkoxysilane

Facile preparation of organic-inorganic hybrid polymeric ionic liquid monolithic column with a one-pot process for protein separation in capillary electrochromatography

An organic-inorganic hybrid monolithic column based on 1-vinyl-3-dodecylimidazolium bromide (VC12Im(+)Br(-)) has been prepared in a single step by combining radical copolymerization with a non-hydrolytic sol-gel (NHSG) process. The NHSG process was significantly shortened to 6 h by using formic acid as catalyst. For comparison, we also prepared polymeric ionic liquid (PIL) monolithic columns by hydrolytic sol-gel and organic polymeric process, respectively. The resulting monolithic columns were characterized by Fourier transform infrared spectra, scanning electron microscopy, and Brunauer-Emmett-Teller. Under the capillary electrochromatography mode, these columns were applied to separate alkylbenzenes, anilines, and proteins, respectively. The results indicated that the NHSG-based hybrid PIL monolithic column exhibited the highest column efficiency among the three types of columns; organic solvent, commonly required by the traditional columns to achieve satisfactory separation efficiency for proteins, was absent in the NHSG-based hybrid PIL monolithic column because of the biocompatibility of the VC12Im(+)Br(-), which was beneficial to analysis of protein containing samples. In order to demonstrate its application potential, the developed NHSG-based hybrid PIL monolithic column was also employed to separate egg white sample.

Silica-particle-supported zwitterionic polymer monolith for microcolumn liquid chromatography

A silica-particle-supported zwitterionic polymeric monolithic column, shortened as supported column (S-column), was prepared by the in situ polymerization of methacrylic acid, ethylene dimethacrylate, and 2-(dimethylamino)ethyl methacrylate in the presence of a ternary porogenic solvent containing water, methanol, and cyclohexanol in a 250 μm id fused-silica capillary prepacked with 5 μm bare silica particles. In the S-column, a thin layer of the polymers was formed around the silica particles in the form of nanoglobules, leaving the interstitial spaces between the particles free for liquid flow. The effects of the preparation conditions on the morphology of the monolith were investigated by scanning electron microscopy and backpressure measurements. The selected volumetric ratio of porogens, monomer concentration, polymerization time, and temperature are 1:1:8 (water/methanol/cyclohexanol), 25% v/v, 5 h, and 60°C, respectively. The S-column was evaluated by comparison with its conventional organic counterpart in terms of morphology, mechanical stability, permeability, swelling-shrinking behavior, capacity, and efficiency. The results demonstrate that the S-column is superior to its counterpart in all the terms with the exception of permeability. The above merits and zwitterionic property of the S-column were further confirmed by separate separations of four inorganic anions and three organic cations.

Study on an electrochromatography method based on organic-inorganic hybrid molecularly imprinted monolith for determination of trace trichlorfon in vegetables

BACKGROUND

Organophosphorus pesticides have been widely used in agricultural production. However, the wide use of organophosphate also results in pesticide residues on the plant, which are harmful to human health because of their potential mutagenic and carcinogenic properties. Therefore, it is vital to develop a sensitive and effective analysis method to control pesticide residues.

RESULTS

In this study, a novel molecularly imprinted capillary monolithic column was prepared using trichlorfon as the template molecule by combining non-hydrolytic sol-gel process with a molecular imprinting technique. The resulting material was characterized by scanning electron microscopy and Fourier transform infrared. Under capillary electrochromatography, the effects of voltage, pH, ACN content and concentration of buffer solution on the electro-osmotic flow (EOF) of imprinted capillary monolithic column were evaluated in detail. Using this prepared material as stationary phase for capillary electrochromatography, a novel method of molecularly imprinted capillary electrochromatography (MICEC) for the detection of trace trichlorfon residues in vegetables was developed. Under optimal conditions, appreciable sensitivity was achieved with a LOD (S/N = 3) of 92.5 µg kg(-1) and method quantitation limit (MQL) of 305.3 µg kg(-1), respectively. The linear ranges of the calibration graph were 0.1 µg L(-1) to 10 mg L(-1). The peak area precision (RSD) for five replicate extractions of 0.01 mg L(-1) trichlorfon standard aqueous solution was 4.5%. To evaluate the accuracy of this method, the blank cucumber and cauliflower samples spiked with trichlorfon were extracted and analyzed by this method with good recoveries, ranging from 80.2% to 95.8%. Moreover, this method was successfully applied to the quantitative detection of the trichlorfon residues in leek samples.

CONCLUSION

With good properties of high sensitivity and simple pre-treatment, this MICEC method could provide a new tool for the rapid determination of trace trichlorfon residue in complex food samples.

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.

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.

A novel C18 reversed phase organic–silica hybrid cationic monolithic capillary column with an ionic liquid as an organic monomer via a “one-pot” approach for capillary electrochromatography

A novel IL hybrid monolithic column with great potential in separation has been fabricated via a “one-pot” approach for capillary electrochromatography

Synthesis and characterization of cellulose 3,5-dimethylphenylcarbamate silica hybrid spheres for enantioseparation of chiral β-blockers

A cellulose derivative-based chiral stationary phase (CSP) is considered one of the most widely applied CSPs due to its powerful enantioseparation ability. The high loading capacity and mechanical strength of CSPs are crucial for their application in preparative chromatography, such as a simulated moving bed. Compared to traditional cellulose-based CSPs that have been adsorbed onto chromatographic supports, organic-inorganic hybrid CSPs exhibit a potentially higher loading capacity and mechanical strength by increasing the density of chiral recognition groups. A hybrid cellulose 3,5-dimethylphenylcarbamate chiral stationary phase (organic/inorganic: 70/30, w/w) was prepared via a sol-gel method and characterized with several analytical techniques, including Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and (29)Si cross polarization/magic angle spinning nuclear magnetic resonance ((29)Si CP/MAS NMR). In addition, the as-synthesized hybrid chiral silica spheres were treated with an end-capping process to mask the residual silica hydroxyl groups. Compared to a commercial Chiralpak IB column, better separation of β-blocker drugs, including pindolol (selectivity of 5.55), metoprolol (2.30), propranolol (1.96), bisoprolol (1.74) and atenolol (1.46), on the end-capped CSP was achieved using liquid chromatography, which suggests that the packing material synthesized in this work has sufficient chiral discriminating ability for the effective separation of β-blocker drugs.

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.

Facile preparation of organic-silica hybrid monolith for capillary hydrophilic liquid chromatography based on "thiol-ene" click chemistry

In this work, a one-step approach to facile preparation of organic-inorganic hybrid monoliths was successfully developed. After vinyl-end organic monomers and azobisisobutyronitrile (AIBN) were mixed with hydrolyzed tetramethoxysilane (TMOS) and 3-mercaptopropyltrimethoxysilane (MPTMS), the homogeneous mixture was introduced into a fused-silica capillary for simultaneous polycondensation and "thiol-ene" click reaction to form the organic-silica hybrid monoliths. By employing this strategy, two types of organic-silica hybrid monoliths with positively charged quaternary ammonium and amide groups were prepared, respectively. The functional groups were successfully introduced onto the monoliths during the sol-gel process with "thiol-ene" click reaction, which was demonstrated by ζ-potential assessment, energy dispersive X-ray spectroscopy (EDX), and Fourier transform infrared (FT-IR) spectroscopy. The porous structure of the prepared monolithic columns was examined by scanning electron microscopy (SEM), nitrogen adsorption-desorption measurement, and mercury intrusion porosimetry. These results indicate the prepared organic-silica hybrid monoliths possess homogeneous column bed, large specific surface area, good mechanical stability, and excellent permeability. The prepared monolithic columns were then applied for anion-exchange/hydrophilic interaction liquid chromatography. Different types of analytes, including benzoic acids, inorganic ions, nucleosides, and nucleotides, were well separated with high column efficiency around 80,000-130,000 plates/m. Taken together, we present a facile and universal strategy to prepare organic-silica hybrid monoliths with a variety of organic monomers using one-step approach.

Cage-like silica nanoparticles-functionalized silica hybrid monolith for high performance capillary electrochromatography via "one-pot" process

A cage-like silica nanoparticles-functionalized silica hybrid monolith for high performance capillary electrochromatography (CEC) has been prepared via "one-pot" process. In this process, the polycondensation of hydrolyzed alkoxysilanes and in situ reaction of mercaptopropyltrimethoxysilane (MPTS) with sodium 3-mercapto-1-propanesulfonate modified octavinyloctasilasesquioxane (MPS-OVS) simultaneously occurred in a pretreated capillary. The characterization and evaluation results indicated that the obtained MPS-OVS hybrid monolithic capillary column has homogeneous macroporous morphology with a permeability of 5.37×10(-13)m(2) and strong electro osmotic flow (EOF) over a wide pH range from 2.7 to 11.2. The EOF on the MPS-OVS hybrid monolithic column reached its maximum of 0.327cm(2)kV(-1)s(-1) at pH 9.7. The best theoretical efficiency of ∼470,000plates/m was obtained for 2-aminophenol in CEC. Anilines and phenols were well separated on the MPS-OVS hybrid monolithic column by CEC, indicating typical reversed-phase and cation-exchange chromatographic retention mechanisms of the column. The monolith was further applied to the separation of bovine serum albumin (BSA) tryptic digests, and the result indicated its potential in the analysis of some complex samples.

Quantification of 5-methylcytosine and 5-hydroxymethylcytosine in genomic DNA from hepatocellular carcinoma tissues by capillary hydrophilic-interaction liquid chromatography/quadrupole TOF mass spectrometry

BACKGROUND

5-Methylcytosine (5-mC) is an important epigenetic modification involved in development and is frequently altered in cancer. 5-mC can be enzymatically converted to 5-hydroxymethylcytosine (5-hmC). 5-hmC modifications are known to be prevalent in DNA of embryonic stem cells and neurons, but the distribution of 5-hmC in human liver tumor and matched control tissues has not been rigorously explored.

METHODS

We developed an online trapping/capillary hydrophilic-interaction liquid chromatography (cHILIC)/in-source fragmentation/tandem mass spectrometry system for quantifying 5-mC and 5-hmC in genomic DNA from hepatocellular carcinoma (HCC) tumor tissues and relevant tumor adjacent tissues. A polymer-based hydrophilic monolithic column was prepared and used for the separation of 12 nucleosides by cHILIC coupled with an online trapping system. Limits of detection and quantification, recovery, and imprecision of the method were determined.

RESULTS

Limits of detection for 5-mC and 5-hmC were 0.06 and 0.19 fmol, respectively. The imprecision and recovery of the method were determined, with the relative SDs and relative errors being <14.9% and 15.8%, respectively. HCC tumor tissues had a 4- to 5-fold lower 5-hmC content compared to tumor-adjacent tissues. In addition, 5-hmC content highly correlated with tumor stage (tumor-nodes-metastasis, P = 0.0002; Barcelona Clinic liver cancer, P = 0.0003).

CONCLUSIONS

The marked depletion of 5-hmC may have profound effects on epigenetic regulation in HCC and could be a potential biomarker for the early detection and prognosis of HCC.

Recent advances in preparation and application of hybrid organic-silica monolithic capillary columns

Hybrid organic-silica monolithic columns, regarded as a second generation of silica-based monoliths, have received much interest due to their unique properties over the pure silica-based monoliths. This review mainly focuses on development in the fields of preparation of hybrid monolithic columns in a capillary and their application for CEC and capillary liquid chromatography separation, as well as for sample pretreatment of solid-phase microextraction and immobilized enzyme reactor since July 2010. The preparation approaches are comprehensively summarized with three routes: (i) general sol-gel process using trialkoxysilanes and tetraalkoxysilanes as coprecursors; (ii) "one-pot" process of alkoxysilanes and organic monomers concomitantly proceeding sol-gel chemistry and free radical polymerization; and (iii) other polymerization approaches of organic monomers containing silanes. The modification of hybrid monoliths containing reactive groups to acquire the desired surface functionality is also described.

Preparation and characterization of hybrid-silica monolithic column with mixed-mode of hydrophilic and strong anion-exchange interactions for pressurized capillary electrochromatography

A novel organic-silica hybrid monolithic stationary phase with a mixed-mode of hydrophilic and strong anion-exchange interactions (HI-SAX) was prepared with a modified "one-pot" process of functional monomers and alkoxysilanes. Using a hydrosoluble initiator 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AIBA), the homogeneous prepolymerization system of this hybrid monolith was successfully obtained by a simple operation. The polycondensation of alkoxysilanes (tetramethoxysilane (TMOS) and vinyl-trimethoxysilane (VTMS)) and the in situ copolymerization of a quaternary ammonium group-containing acrylic monomer ([2-(acryloyloxy)ethyl] trimethyl ammonium methyl sulfate (AETA)) on the precondensed siloxanes were achieved. The morphologies of the hybrid-silica monolithic matrixes were observed by SEM, and the performances of the organic-silica hybrid monolithic columns were investigated by pressurized capillary electrochromatography. The mechanical stability and reproducibility of the obtained hybrid monolithic column preformed acceptable. Both hydrophilic interaction chromatography mechanism and strong anion-exchanged interaction were investigated. A mixed mode of HI-SAX was obtained for the analysis of nucleotides with a good resolution, and the separation of polar and basic nucleic acid bases and nucleosides was also achieved without peak tailing.

Synthesis and characterization of a hydrogel with controllable electroosmosis: a potential brain tissue surrogate for electrokinetic transport

Electroosmosis is the bulk fluid flow initiated by application of an electric field to an electrolyte solution in contact with immobile objects with a nonzero ζ-potential such as the surface of a porous medium. Electroosmosis may be used to assist analytical separations. Several gel-based systems with varying electroosmotic mobilities have been made in this context. A method was recently developed to determine the ζ-potential of organotypic hippocampal slice cultures (OHSC) as a representative model for normal brain tissue. The ζ-potential of the tissue is significant. However, determining the role of the ζ-potential in solute transport in tissue in an electric field is difficult because the tissue's ζ-potential cannot be altered. We hypothesized that mass transport properties, namely the ζ-potential and tortuosity, could be modulated by controlling the composition of a set of hydrogels. Thus, poly(acrylamide-co-acrylic acid) gels were prepared with three compositions (by monomer weight percent): acrylamide/acrylic acid 100/0, 90/10, and 75/25. The ζ-potentials of these gels at pH 7.4 are distinctly different, and in fact vary approximately linearly with the weight percent of acrylic acid. We discovered that the 25% acrylic acid gel is a respectable model for brain tissue, as its ζ-potential is comparable to the OHSC. This series of gels permits the experimental determination of the importance of electrokinetic properties in a particular experiment or protocol. Additionally, tortuosities were measured electrokinetically and by evaluating diffusion coefficients. Hydrogels with well-defined ζ-potential and tortuosity may find utility in biomaterials and analytical separations, and as a surrogate model for OHSC and living biological tissues.