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Chiral compounds are known to be important not only because they are the fundamental components of living organisms, but also for their unique chiroptical properties. In recent years, scientists have fabricated several chiral organic supramolecular aggregates by using chiral physical fields, such as vortex flow. Herein, the relationship between dynamic chiroptical properties and rheological nature is discussed, suggesting the shear thinning properties of non-Newtonian fluids might help colloidal particles adopt a chiral arrangement in vortices. Furthermore, the storage modulus of colloids could be increased by adding a linking agent, which successfully kept the dynamic chiroptical properties in the static state. Moreover, the salt effect on the host-guest interaction involved in the colloids was studied, the results suggested a significant enhancement of the transferred dynamic circular dichroism for the achiral guest molecule., (© 2021 Wiley-VCH GmbH.)

Recently, scientists have reported a range of chiral fluorescence materials or chiral composites that can emit circularly polarized luminescence. Herein, two achiral metal-organic colloidal solutions were studied, showing active circularly polarized luminescence, which is observed in vortex stirring. The absolute values for g lum are 0.05 and 0.03 and the plus or minus sign of g lum depends on the colloidal structure and stirring direction, which make the property easy to manipulate. Further, the host-guest interaction study suggests both electrostatic interactions and coordination bonding may influence the chiroptical property from the colloidal solution to the guest molecule. Rhodamine 6G and its carboxylic acid derivative exhibit good quantum yields and acceptable g lum values in the colloidal solution., (© 2021 Wiley-VCH GmbH.)

A functional stainless steel microextraction fiber easily prepared by in situ growing metal-organic framework UiO-66 was presented and used for high-performance analysis of polycyclic musks. Via the robust Ag-SH bonding reaction, mercaptoacetic acid was easily anchored on Ag film to provide carboxyl group on the stainless steel fiber, then in situ grown UiO-66 was fulfilled via the coordination reaction between Zr 4+ and carboxyl group. Good characteristics including large surface area, high thermal stability, and good adsorption property were achieved. Sensitive detection limits (0.015-0.040 ng/L) were achieved for polycyclic musks by coupling with gas chromatography with mass spectrometry, and it could be stable enough for 150 extraction cycles without a significant loss of extraction efficiency. Compared with the classical commercial fibers, 2.2-11.4 times higher enhancement factors were shown. Applied to the analysis of fortified river water samples, five typical polycyclic musks were well detected with the recoveries of 90.2-101.8%, respectively. It showed a facile approach for preparing stainless steel microextraction fiber via chemically bonding in situ grown metal-organic framework for high-performance enrichment., (© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Developing a high-performance modification protocol is critical for efficiently fabricating affinity monolith. Herein, by using 2,4,6-trichloro-1,3,5-triazine as the linker, a simple triazine-bridged approach was proposed for efficiently fabricating aptamer-grafted polyhedral oligomeric silsesquioxane-polyethyleneimine affinity monolith with high specificity toward ochratoxin A. Experimental parameters, column characteristics and specificity performances of the resultant affinity monolith were investigated in detail. Under the optimal conditions, 2,4,6-trichloro-1,3,5-triazine was rapidly grafted on the polyamine matrix, and effectively applied to the subsequent bridge linkage of aptamers. It was simple and effective, which resulted in a significant decrease of modification time, excellent properties including the high coverage density of aptamer up to 1799 pmol/μL and sensitive detection of ochratoxin A as low as 10 pg/mL in beer samples. This protocol provides a facile approach for fabricating aptamer-grafted polyamine affinity monoliths with highly selective discrimination performance., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A strategy on amperometric detection for CZE of phenol carbamates as model analytes with a facile in-line thermal hydrolysis was presented, in which a thermal hydrolysis, subsequent CZE separation and final column-end amperometric detection were accomplished in an intact capillary. Key parameters of hydrolysis dynamics of carbamates and electrochemical detection of the hydrolysates were studied, as well as electrophoretic conditions. Under the optimal conditions, the capillary was utilized as chambers for in situ hydrolysis, CZE separation, and electrochemical detection. The successive separation of hydrolysates of five carbamates (propoxur, carbofuran, 3-OH-carbofuran, carbaryl and bendiocarb) were achieved within 17 min. Applied to vegetable samples, the recoveries of carbamates fortified at 0.02 and 0.05 mg/kg were ranging in 88-107.2 and 86.3-107.3%, respectively. The success in the implementation of such a scheme resulted in a simple instrument as compared with those current analytical methods with post-column derivization or pre-column hydrolysis, or online enrichment in chip, respectively. This protocol might possess a potential utility for the sensitive amperometric detection of phenol carbamates., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

An organic-silica hybrid monolith was prepared by a single-step ring-opening polymerization of octaglycidyldimethylsilyl polyhedral oligomeric silsesquioxane (POSS-epoxy), polyethylenimine (PEI), and β-cyclodextrin (β-CD) in a ternary porogenic solvent consisting of polyethylene glycol, 1,4-butanediol, and 1-propanol. The framework of POSS-PEI hybrid monolith could offer well-defined 3D skeleton, while β-CD with the ability of forming a host-guest inclusion complexes with a variety of compounds could show an ability of specific selection. The obtained hybrid monoliths were successfully applied for separation of phenols, benzoic acids, and nucleobases. Especially due to the introduction of β-CD, positional isomers including hydroquinone and resorcinol, o-nitrophenol and p-nitrophenol, as well as p-chlorophenol and o-chlorophenol were baseline separated and the column efficiency reached 82 300 plates/m for hydroquinone., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Via the facile ring-opening reaction of epoxy groups with quinine, a novel polymer monolith with quaternary ammonium for reversed-phase/strong anion-exchange mixed-mode has been fabricated for pressurized capillary electrochromatography (pCEC). Optimization on the preparation of quinine-modified monoliths has been investigated, and characteristics including morphology, permeability, mechanical stability, reproducibility, and column performance have been also studied. Active quaternary ammonium groups were conveniently produced to generate cationic action sites and stable anodic electroosmotic flow. Multiple interactions including reversed-phase, strong anion-exchange, electrostatic repulsion and π-π stacking interactions were obtained. Satisfactory separation capability of various analytes such as alkylbenzenes, polycyclic aromatic hydrocarbons, benzoic acid and its homologs, and β 2 -receptor excitants has been achieved. Applied to the real sample, the good resolution of three alkaloids in Corydalis yanhusuo were achieved by pCEC with the quinine-modified monolith. The results light a potential access to facilely fabricating quaternary ammonium-functionalized polymer monolith with multiple interactions for efficient electrochromatography profiling of various compounds., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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 78 000 plates/m., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A novel o-phenanthroline-immobilized ionic-liquid-modified hybrid monolith for capillary electrochromatography was synthesized based on chloropropyl-silica, which was prepared by the in situ polymerization of tetramethoxysilane and 3-chloropropyltrimethoxysilane via a sol-gel process. The morphology of the hybrid monolith was characterized by scanning electron microscopy, and relatively stable anodic electroosmotic flow was observed under a broad pH ranged from pH 3.0 to 9.0. The separation mechanism was investigated by separating four neutral molecules (toluene, dimethylformamide, formamide, and thiourea). The obtained hybrid monolith possessed an obviously reversed-phase retention mechanism, but when the acetonitrile content in the mobile phase was >90% v/v, a weak hydrophilic mechanism was observed on the resultant o-phenanthroline-modified chloropropyl-silica hybrid monolith. The reproducibility of the column was also investigated by measuring relative standard deviations of the migration time for four neutral molecules. Relative standard deviations of run to run (n = 3), day to day (n = 3), and column to column (n = 3) were in the range of 0.4-0.7, 0.9-2.1, and 1.4-3.3%, respectively. Basic separations of various polar analytes including phenols and aromatic amines were successfully achieved., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A novel phenylalanine (Phe) functionalized zwitterionic monolith for hydrophobic electrochromatography was prepared by a two-step procedure involving the synthesis of glycidyl methacrylate based polymer monolith and subsequent on-column chemical modification with Phe via ring-opening reaction of epoxides. Benefitting from the hydrophobicity of both methacrylate-based matrix and aromatic group of Phe, this monolith could exhibit good hydrophobic interaction for the separation. Typical RP chromatographic behavior was observed toward various solutes. The well-controlled cathodic or anodic EOF of the prepared column could be facilely switched by altering the pH values of running buffers. The separation mechanism of this Phe functionalized zwitterionic monolith is discussed in detail. Two mixed-mode mechanisms of RP/cation exchange and RP/anion exchange could be further realized on the same monolith in different pH condition of the mobile phase. Versatile separation capabilities of neutral, basic, and acidic analytes have been successfully achieved in this zwitterionic monolith by CEC method., (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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., (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A highly sensitive capillary electrophoretic profiling of nicotine (NIC) and nornicotine (NNIC) was developed and applied to mushrooms with amperometric detection (AD). Effects of the experimental factors including detection potential, separation parameters, and sample pretreatment conditions were investigated. Under the optimal conditions, the electrophoretic analysis of NIC and NNIC was achieved within 8 min on a pencil carbon disc working electrode at 0.95 V, which was lower than those reported previously. Good calibration curves were obtained in 0.01-2.0 μg/mL and 0.02-3.0 μg/mL with the LOD of 2 ng/mL and 5 ng/mL for NIC and NNIC, respectively. The feasibility of the resultant method was verified. Average recoveries of different fortified levels ranged in 80.7-86.0% and 94.0-98.6% for NNIC and NIC were gained, respectively. Applied to a range of mushrooms (Boletus edulis and Lentinus edodes), the NIC contained naturally was successfully found in the level of 19.71-79.20 μg/kg. The results obtained with CE-AD method were acceptable and close to that of HPLC-MS., (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A novel open-tubular CEC column coated with chitosan-graft-(β-CD) (CDCS) was prepared using sol-gel technique. In the sol-gel approach, owing to the 3D network of sol-gel and the strong chemical bond between the stationary phase and the surface of capillary columns, good chromatographic characteristics and unique selectivity in separating isomers were shown. The column efficiencies of 55,000∼163,000 plates/m for the isomeric xanthopterin and phenoxy acid herbicides using the sol-gel-derived CDCS columns were achieved. Good stabilities were demonstrated that the RSD values for the retention time of thiourea and isoxanthopterin were 1.3 and 1.4% (run to run, n = 5), 1.6 and 2.0% (day to day, n = 3), 2.9 and 3.1% (column to column, n = 3), respectively. The sol-gel-coated CDCS columns have shown improved separations of isomeric xanthopterin in comparison with CDCS-bonded capillary column., (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A novel tentacle-type polymer stationary phase covalently modified with branched polyethyleneimine (PEI) was developed for peptides and proteins separations by open-tubular CEC (OT-CEC). The preparation procedure included the silanization of capillary inner wall, in situ graft polymerization and PEI functionalization. A wrinkly polymer surface of multitudinous steric amine groups was evenly formed on the capillary inner wall, and anodic EOF could be gained within a wide pH range of 2.5-7.5. The electroosmotic mobility was examined for its dependence on pH as well as PEI concentrations. Good repeatability was gained with RSD for the migration time of EOF marker within 4.8% and satisfactory chemical stability was validated. Due to the existence of amine groups on the surface of tentacle-type polymer stationary phase, the silanol effect that occurs between the positively charged biomolecules and the silanols of the capillary column was greatly suppressed. Compared with a monolayer-coating capillary, seven enkephalin-related peptides were well resolved on the PEI-bonded column with high efficiencies. Favorable separations of peptides and proteins with high column efficiencies were obtained in 144,000-189,000 and 97,000-170,000 plates/m. Branched PEI-bonded tentacle-type polymer stationary phase has been proven to afford satisfactory retention and resolution of peptides and proteins., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A multi-functional open-tubular (OT) column covalently modified with [3-(phenylamino)propyl]trimethoxysilane (PPTMS) via a single-step silanization reaction has been developed, and employed for alkaloids and aromatic acids analytes by CEC. Both anodic and cathodic EOF could be gained in the PPTMS-bonded column, and anodic EOF was exhibited when the pH of running buffer was less than 8.0. Using thiourea as the EOF marker, a satisfactory column stability was denoted, and the RSD values for migration time and peak area were gained at 0.5 and 3.7% (intra-day, n=5), 1.7 and 5.6% (inter-day, n=3), 3.9 and 5.8% (column-to- column, n=16 in four batches). With anodic EOF mode (pH=2.0 of 10 mmol/L phosphate buffer), favorable separations of cationic alkaloids (viz. uridine, adenosine, cytidine, adenine, cytosine) were successfully achieved with column efficiencies ranging from 95,000 to 187,000 plates/m, and the undesired adsorption on the inter-wall of capillary column could be avoided. Besides, six anionic aromatic acids could be also separated efficiently in the co-electroosmotic mode with anodic EOF. And high efficiencies ranged from 176,000 to 235,000 plates/m were gained with a good repeatability. PPTMS-bonded capillary column might be used as an alternative functional medium to physical coating capillary column for the analyses of aromatic organic acids and bases., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A multi-functional separation column modified with 3-[2-(2-aminoethylamino)ethylamino] propyl-trimethoxysilane was developed for open tubular capillary electrochromatography. This functional hydrophilic triamine-bonded open tubular column could generate both anodic and cathodic EOF. When the pH of the running buffer was below 5.3 (30% 3-[2-(2-aminoethylamino)ethylamino] propyl-trimethoxysilane, v/v), the anodic EOF was exhibited, which greatly prevented the undesired adsorptions of basic proteins on the capillary inner wall. Favorable separation of four basic proteins (viz. trypsin, ribonuclease A, lysozyme and cytochrome c) was successfully achieved at pH 3.5 of 10  mmol/L phosphate buffer. The column efficiencies of proteins were in the range from 87,000 to 110,000  plates/m, and the RSD values for migration time of four proteins were less than 1.2% (run-to-run, n=5). The ionic analytes were also separated efficiently in the co-electroosmotic mode. The average efficiencies ranged from 81,000 to 190,000  plates/m for seven aromatic acids and 186,000-245,000  plates/m for four nucleoside monophosphates, respectively, and good capillary column repeatability was gained with RSD of the migration time not more than 3.0%. The triamine-bonded open tubular capillary column is favorable to be an alternative functional medium for the further analysis of basic proteins and anionic analytes.

A novel monolithic stationary phase with mixed mode of hydrophilic and strong anion exchange (SAX) interactions based on in situ copolymerization of pentaerythritol triacrylate (PETA), N,N-dimethyl-N-methacryloxyethyl N-(3-sulfopropyl) ammonium betaine (DMMSA) and a selected quaternary amine acrylic monomer was designed as a multifunctional separation column for CEC. Although the zwitterionic functionalities of DMMSA and hydroxy groups of PETA on the surface of the monolithic stationary phase functioned as the hydrophilic interaction (HI) sites, the quaternary amine acrylic monomer was introduced to control the magnitude of the EOF and provide the SAX sites at the same time. Three different quaternary amine acrylic monomers were tested to achieve maximum EOF velocity and highest plate count. The fabrication of the zwitterionic monolith (designated as HI and SAX stationary phase) was carried out when [2-(acryloyloxy)ethyl]trimethylammonium methylsulfate was used as the quaternary amine acrylic monomer. The separation mechanism of the monolithic column was discussed in detail. For charged analytes, a mixed mode of HI and SAX was observed by studying the influence of mobile phase pH and salt concentration on their retentions on the poly(PETA-co-DMMSA-co-[2-(acryloyloxy)ethyl]trimethylammonium methylsulfate) monolithic column. The optimized monolith showed good separation performance for a range of polar analytes including nucleotides, nucleic acid bases and nucleosides, phenols, estrogens and small peptides. The column efficiencies greater than 192 000 theoretical plates/m for estriol and 135 000 theoretical plates/m for charged cytidine were obtained.

A polymethacrylate-based molecularly imprinted monolithic column bearing mixed functional monomers, using non-covalent imprinting approach, was designed for the rapid separation of nitroimidazole compounds. The new monolithic column has been prepared via simple in situ polymerization of 2-hydroxyethyl methacrylate, dimethylaminoethyl methacrylate and ethylene dimethacrylate, using (S)-ornidazole ((S)-ONZ) as template in a binary porogenic mixture consisting of toluene and dodecanol. The composition of the polymerization mixture was systematically altered and optimized by altering the amount of monomers as well as the composition of the porogenic solvent. The column performance was evaluated in pressure-assisted CEC mode. Separation conditions such as pH, voltage, amount of organic modifier and salt concentration were studied. The optimized monolithic column resulted in excellent separation of a group of structurally related nitroimidazole drugs within 10 min in isocratic elution condition. Column efficiencies of 99 000, 80 000, 103 000, 60 000 and 99 000 plates/m were obtained for metronidazole, secnidazole, ronidazole, tinidazole and dimetridazole, respectively. Parallel experiments were carried out using molecularly imprinted and non-imprinted capillary columns. The separation might be the result of combined effects including hydrophobic, hydrogen bonding and the imprinting cavities on the (S)-ONZ-imprinted monolithic column.

Molecularly imprinted polymer (MIP) monoliths with (S)-ornidazole ((S)-ONZ) as the template molecule have been designed and prepared by the simple thermal polymerization of methacrylic acid, 4-vinylpyridine, and ethylene dimethacrylate in the presence of a binary porogenic mixture of toluene and dodecanol. The influences of polymerization mixture composition on the chiral recognition of ONZ have been evaluated, and the imprint effect in the optimized MIP monolith has been clearly demonstrated. The new monolithic stationary phase with optimized porous property and good selectivity was used for the chiral separation of ONZ by pressurized CEC. The pressurized CEC conditions were also optimized to obtain the good chiral separation. The enantiomers were rapidly separated within 9 min on the MIP-based chiral stationary phase, whereas the chiral separation was not obtained on the nonimprinted polymer. Additionally, the proposed method has been successfully applied to the chiral separation of ONZ in tablet samples by injection of the crude sample. The cross-selectivity for similar antiparasitic drug was investigated. The results indicated that the chiral separation of secnidazole could also be obtained on the optimized MIP monolith within 14 min.

A porous zwitterionic monolith was prepared by in situ covalent attachment of lysine to a gamma-glycidoxypropyltrimethosysilane-modified silica monolith. The prepared column was used to perform neutral and ionized solutes separations by pressurized (pCEC). Due to the zwitterionic nature of the resulting stationary phase, the monolithic column provided both electrostatic attraction and repulsion sites for electrochromatographic retention for ionized solutes. Separation of several nucleotides was investigated on the monolithic column. It was shown that the nucleotides could be separated based on hydrophilic and electrostatic interactions between the stationary phase and analyte. Besides, the separation property of the zwitterionic silica monolith was compared with the use of diamine-bonded silica monolith as stationary phase. As expected, the lysine monolith exhibited a lower retention for the five nucleotides, which was due to the dissociation of the external carboxylic acid groups, leading to electrostatic repulsion with negatively charged solutes. Under the same experimental conditions, separation of the five nucleotides on the zwitterionic column was in less than 8 min, while that on the diamine column was in approximately 60 min.

A neutral, nonpolar monolithic capillary column was evaluated as a hydrophobic stationary phase in pressurized CEC system for neutral, acidic and basic solutes. The monolith was prepared by in situ copolymerization of octadecyl methacrylate and ethylene dimethacrylate in a binary porogenic solvent consisting of cyclohexanol/1,4-butanediol. EOF in this hydrophobic monolithic column was poor; even the pH value of the mobile phase was high. Because of the absence of fixed charges, the monolithic capillary column was free of electrostatic interactions with charged solutes. Separations of neutral solutes were based on the hydrophobic mechanism with the pressure as the driving force. The acidic and basic solutes were separated under pressurized CEC mode with the pressure and electrophoretic mobility as the driving force. The separation selectivity of charged solutes were based on their differences in electrophoretic mobility and hydrophobic interaction with the stationary phase, and no obvious peak tailing for basic analytes was observed. Effects of the mobile phase compositions on the retention of acidic compounds were also investigated. Under optimized conditions, high plate counts reaching 82,000 plates/m for neutral compounds, 134,000 plates/m for acid compounds and 150,000 plates/m for basic compounds were readily obtained.

A new method, pressurized CEC with end-column amperometric detection using carbon paste electrode, has been developed for the separation and determination of five phenolic xenoestrogens in chicken eggs and milk powder samples. Efficient separation of five analytes was performed by pressurized CEC using a mobile phase consisting of 60% v/v ACN and 40% v/v Tris buffer (5 mmol/L, pH 8.0), +6 kV of applied voltage and 7.0 MPa of supplementary pressure. Detection limits of 50, 5, 2, 10 and 20 ng/mL for pentachlorophenol, bisphenol-A, 2,4-dichlorophenol, 4-tert-octylphenol and 4-nonylphenol, respectively, were achieved using carbon paste electrode as working electrode and +0.8 V as detection potential. Matrix solid phase dispersion extraction method had been employed during sample preparation procedure, and mean recoveries ranged from 79.2 to 102.6% at different concentrations of phenolic xenoestrogens for spiked egg and milk powder samples were obtained.

A novel zwitterionic monolith was prepared by in situ covalent attachment of glycin to a gamma-glycidoxypropyltrimethoxysilane-modified silica monolith. The monolith possessing in its structure bonded secondary amine groups and carboxylic acid groups was evaluated in pressurized CEC (pCEC) system using small neutral and charged solutes. Owing to the zwitterionic nature of the resulting stationary phase, the direction and magnitude of EOF in this column could be manipulated by adjusting the pH values of the mobile phase. Typical hydrophilic interaction was observed when the ACN content exceeded 45%. Separations of acidic and basic compounds were performed on the prepared column in weakly anodic and cathodic EOF modes, respectively. The organic solvent composition, the salt concentration, and the pH of the mobile phase have effects on the electrochromatographic retention. Besides the hydrophilic interaction and electrophoretic mechanism, electrostatic interactions are also involved in the separations of acids and bases on the zwitterionic column.

A novel polymethacrylate-based monolithic column with covalently bonded zwitterionic functional groups was prepared by in situ copolymerization of N,N-dimethyl-N-methacryloxyethyl N-(3-sulfopropyl) ammonium betaine (SPE), pentaerythritol triacrylate (PETA), and vinylsulfonic acid (VS) in a binary porogenic solvent consisting of cyclohexanol and ethylene glycol. This monolith was developed as a separation column for CEC. While SPE functioned as both an electrostatic interaction stationary phase and the polar ligand provider, VS was employed to generate EOF. PETA, which has much more hydrophilicity due to a hydroxyl sub-layer, was used to replace ethylene dimethacrylate as a cross-linker. The monolith provided an adequate EOF when VS level was maintained at 0.6% w/w. Different monolithic stationary phases were easily prepared by adjusting the ratio of PETA/SPE in the polymerization solution as well as the composition of the porogenic solvent. The observed RSD were

A method was developed to quantify domoic acid (DA), the chemical responsible for amnesic shellfish poisoning (ASP), by pressurized CEC (pCEC). The effect of different experimental conditions on the separation of DA and matrix solutes, such as the content of ACN in mobile phase, pH and concentration of buffer, supplementary pressure and applied voltage, were investigated. Under the optimal conditions, the pCEC method separated DA from shellfish matrices within 6 min. By using supplementary pressure, bubble formation in the capillary column was completely suppressed. The method was repeatable, sufficient accurate and sensitive for rapid screening of DA in shell seafood.

A novel porous polymethacrylate-based monolithic column by in situ copolymerization of 3-sulfopropyl methacrylate (SPMA) and pentaerythritol triacrylate in a binary porogenic solvent consisting of cyclohexanol/ethylene glycol was prepared. The monolith possessed in their structures bonded sulfonate groups and hydroxyl groups and was evaluated as a hydrophilic interaction and strong cation-exchange stationary phases in capillary liquid chromatography (cLC) and pressure-assisted CEC using small polar neutral and charged solutes. While the SPMA was introduced as multifunctional monomer, the pentaerythritol triacrylate was used to replace ethylene glycol dimethacrylate as cross-linker with much more hydrophilicity due to a hydroxyl sub-layer. The different characterization of monolithic stationary phases were specially designed and easily prepared by altering the amount of SPMA in the polymerization solution as well as the composition of the porogenic solvent for cLC and pressure-assisted CEC. The resulting monolith showed the different trends about the effect of the permeabilities on efficiency in the pressure-assisted CEC and cLC modes. A typical hydrophilic interaction chromatography mechanism was observed at higher organic solvent content (ACN%>70%) for polar neutral analytes. For polar charged analytes, both hydrophilic interaction and electrostatic interaction contributed to their retention. Therefore, for charged analytes, selectivity can be readily manipulated by changing the composition of the mobile phase (e.g., pH, ionic strength and organic modifier). With the optimized monolithic column, high plate counts reaching greater than 170 000 plates/m for pressure-assisted CEC and 105 000 plates/m for cLC were easily obtained, respectively.

A silica-based monolith as polar stationary phase was described for hydrophilic interaction pressurized capillary electrochromatography (HI-pCEC). The polar monolithic column was prepared by on-column reaction of lysine with epoxy groups on a gamma-glycidoxypropyltrimethosysilane-modified silica monolith. The stationary phase yielded strong hydrophilic interaction due to the slightly polar hydroxyl groups, and the strong polar lysine ligand with amino groups and carboxylic groups contained on the surface of the monolith. In order to evaluate the hydrophilic character of lysine ligand, the chromatographic behaviors of epoxy monolith (before lysine bonded) and diol monolith (hydroxyl groups contained) were also investigated. Two groups of comparative experiment were developed in terms of the separation of typical neutral non-polar and polar compounds performed in a mobile phase of aqueous-acetonitrile solution. Results showed that the lysine monolith was much more hydrophilic than the diol monolith, which presented less hydrophobic than the epoxy monolith. For further study on its hydrophilic character, the lysine monolith was demonstrated in the HI-pCEC mode for the separations of various polar compounds such as phenols, nucleic acid bases and nucleosides.

A pressurized CEC (pCEC) coupled with on-column chemiluminescence (CL) detection was developed for direct determination of amino acids, which was based on the principle of an enhanced effect of Cu(II)-amino acid complexes on the CL reaction between luminol and hydrogen peroxide in alkaline solution. The effects of some important factors on pCEC separation and CL intensity were systemically investigated. Baseline separation of amino acids including L-histidine (L-His), L-threonine (L-Thr), and L-tyrosine (L-Tyr) was achieved by using a monolithic column with a mobile phase of 5.0x10(-3) mol/L phosphate buffer at pH 8.0 that contained 25% v/v methanol and 5.0x10(-4) mol/L luminol and 1.0x10(-5) mol/L Cu(II) at an applied voltage of -5 kV. The calibration curves of the analytes by plotting the peak height against corresponding concentration were linear over the range of 3.2x10(-6)-3.2x10(-4) mol/L for L-His, 4.1x10(-6)-4.1x10(-4) mol/L for L-Thr, and 6.0x10(-7)-3.0x10(-4) mol/L for L-Tyr. The LODs for L-His, L-Thr, and L-Tyr were 6.4x10(-7), 8.4x10(-7), and 3.0x10(-7) mol/L (S/N = 2), respectively. The proposed method was applied to the analysis of amino acid injection sample with satisfactory results. Mean recoveries for three amino acids were from 84.3 to 89.6%.

A novel silica monolithic stationary phase functionalized with 3-(2-aminoethylamino)propyl ligands for pressurized CEC has been presented. The monolithic capillary columns were prepared by a sol-gel process in 75 microm id fused-silica capillaries and followed by a chemical modification. The diamino groups on the surface of the stationary phase are meant to generate the chromatographic surface and a substantial anodic EOF as well as to provide electrostatic interaction sites for charged solutes. The electrochromatographic characterization and column performance were evaluated by a variety of neutral and charged solutes. It was observed that the anodic EOF for the diamine-bonded monolith was greatly affected by the reaction time with 3-(2-aminoethylamino)propyltrimethoxysilane and the PEG amount in the sol-gel reaction mixture in addition to the mobile phase conditions. The monolithic stationary phase exhibited hydrophilic interaction chromatographic behavior toward neutral solutes. Good separations of various solutes including phenols, nucleic acid bases, nucleosides and nucleotides were achieved under different experimental conditions. Fast and efficient separations were obtained with high plate counts reaching more than 130,000 plates/m.

A monolithic capillary column with double mixed-modes of hydrophilic interaction/cation-exchange and RP/cation-exchange stationary phase was prepared by in situ thermal polymerization and then hydrolyzed with hydrochloric acid. The polymerization solution containing glycidyl methacrylate (GMA), 3-sulfopropyl methacrylate potassium salt (SPMA), and ethylene dimethacrylate (EDMA) in a binary porogenic solvent consisting of dimethylformamide (DMF) and 1,4-butanediol was polymerized in a fused-silica capillary pretreated with 3-(trimetoxysilyl) propyl methacrylate. The epoxy groups on the surface were hydrolyzed to diol groups with hydrochloric acid to enhance the polarity of the stationary phase. By simply altering the ACN content in the mobile phase, two mixed-mode mechanisms could be achieved on the same monolithic column in different mobile phase condition. Hydrophilic interaction (or hydrophilic interaction/cation-exchange) was observed at high ACN content, as well as RP (or RP/cation-exchange) was observed at low ACN content. The monolithic column provided good selectivity and high efficiency for separation of neutral polar analytes and basic compounds. Phenols, anilines, alkaloids, nucleic acid bases, and narcotic pharmaceuticals have been successfully separated. Effects of salt concentration and ACN content on the separation have also been investigated. High column efficiencies of up to 352 000 plates/meter were obtained by the separation of narcotic pharmaceuticals.

A system of off-column coaxial flow chemiluminescence (CL) detection coupled to pressurized CEC (pCEC) was described. The interface utilized a reactor that introduced postcolumn CL reagent into the capillary effluents in a sheathing flow profile. To compare and evaluate band broadening of analytes caused by the detector, the typical CL compounds luminol and N-(4-aminobutyl)-N-ethylisoluminol (ABEI) were separated and detected by pCEC or capillary HPLC (cHPLC) coupled to CL and UV detector, respectively. The results demonstrated that the band broadening caused by off-column detection interface was minimized due to the fast kinetic nature of the CL reaction. With the proposed pCEC-CL system, the detection limits of luminol and ABEI were 1.0x10(-8) and 8.0x10(-8) mol/L, respectively, which were approximately 100-fold more sensitive than those obtained with UV absorption. In addition, separation and detection of the ABEI-labeled L-lysine (L-Lys) and L-arginine (L-Arg) were accomplished by pCEC-CL method based on the principle of ABEI-potassium ferricyanide-alkaline medium CL reaction system. Under the optimum conditions, good results could be achieved compared with pCEC-UV.

A method for the separation and determination of five major opium alkaloids (narcotine, papaverine, thebaine, codeine, and morphine) in pericarpium papaveris by pressurized CEC (pCEC) with monolithic column has been developed. Under the optimum condition, linear calibration ranges of narcotine, papaverine, thebaine, codeine, and morphine were obtained as 2-85, 2-85, 5-75, 10-65, and 10-65 microg/mL, respectively. LODs of these analytes were 1.5-6.0 microg/mL. The RSD (n=7) of the migration time and peak area were 1.94-5.24 and 4.05-8.21%, respectively. The proposed method was successfully applied to the analysis of pericarpium papaveris samples. Average recoveries of 79.0-95.9% at different fortified levels of alkaloids were achieved with RSD less than 4.6%. Meanwhile, the mechanism of the separation of the alkaloids on the monolithic column was also discussed. The result showed that the separation of alkaloids was mainly based on the mixed mode of hydrophilic interaction (HI) and cation exchange.

A monolithic stationary phase was prepared in a single step by in situ copolymerization of iso-butyl methacrylate (IBMA), ethylene dimethacrylate (EDMA), and N,N-dimethylallylamine (DMAA) in a binary porogenic solvent consisting of N,N-dimethylformamide (DMF) and 1,4-butanediol. As the frame structures of monoliths, the amino groups are linked to support the EOF necessary for driving the mobile phase through the monolithic capillary, while the hydrophobic groups are introduced to provide the nonpolar sites for the chromatographic retention. To evaluate the column performance, separations of typical kinds of neutral or charged homologs, such as alkylbenzenes, phenols (including isomeric compounds of hydroquinone, resorcin, and catechol), and anilines (including isomeric compounds of o-phenylenediamine and 1,4-phenylenediamine), were performed, respectively on the prepared column under the mode of pressurized pCEC. Effects of the buffer pH and the mobile phase composition on the linear velocity of mobile phase and the retention factors of these compounds were investigated. It was found that the retention mechanism of charged solutes could be attributed to a mixed mode of hydrophobic interaction and electrophoresis, while an RP chromatographic behavior on the monolithic stationary phases was exhibited for neutral solutes. Especially, basic compounds such as anilines were well separated on the monolithic columns in the "counterdirectional mode," which effectively eliminated the electrostatic adsorption of basic analytes on the charged surface of the stationary phases.

A new analytical method, pressurized CEC (pCEC) with amperometric detection (AD) using 1.5 microm RP nonporous silica packed columns has been developed for the rapid separation and determination of four Sudan dyes in hot chilli. The influence of several experimental parameters on the retention behavior has been investigated. The electrochemical oxidation of Sudans I-IV separated by pCEC can be reliably monitored with a carbon electrode at +0.95 V (vs. Ag/AgCl). Fast and efficient separation of the analytes was achieved within 7 min by pCEC under the optimum conditions with an ACN/water (95:5%) mobile phase containing formic acid (pH 4.3), 5% acetone and 0.002% triethylamine using a separation voltage of 12 kV. The detection limits for four Sudan dyes ranged from 8.0 x 10(-7) to 1.2 x 10(-6) mol/L. To evaluate the feasibility and reliability of this method, the proposed pCEC-AD method was further demonstrated with hot chilli samples spiked with Sudan dyes.

MEKC was used in conjunction with end-column amperometric detection (AD) at a carbon disc electrode (0.3 mm diameter) for the selective and sensitive determination of melatonin and its five related indoleamines including its precursors and metabolites in the pineal gland. The introduction of a sample stacking technique in injection and the buffer additive SDS in the buffer solution system provided the rapid and sensitive analysis. Optimal buffer conditions (10 mmol/L phosphate containing 20 mmol/L SDS, pH 7.2), detection potential (+1.0 V vs. Ag/AgCl), and electrokinetic injection 10 s with the separation voltage of 24 kV were employed to achieve the baseline separation of six pineal hormones within 15 min. The peak currents and the analyte concentrations have a good linear relationship over the range of 6.0 x 10(-8) 6.0 x 10(-5 )mol/L. The detection limits for six pineal hormones by AD are 9.7 to 41.8 nmol/L (equal to 2.0 to 9.7 ng/mL) (S/N = 3), respectively. It is proved to provide about 30- to 250-fold improvement over UV, and be comparable with the sensitive fluorescence detection, which needs pre-column derivatization. The proposed method has been applied for analysis of melatonin and related indoleamines in rat pineal glands. A very simple sample pretreatment procedure, merely involving the homogenization step in perchloric acid, was enough to achieve recoveries in the range of 71 to 127% for all the analytes in the pineal gland.

A silica-based monolithic column as polar stationary phase is proposed for pressurized CEC (pCEC). The monolithic silica matrix from a sol-gel process was chemically modified by 3-aminopropyltrimethoxysilane to produce a column for hydrophilic interaction applications. The amino groups on the surface of the polar stationary phase generated anodic EOF under acidic conditions and served at the same time as a weak anion-exchanger. The anion solutes such as nucleotides were separated by the mixed mode mechanism, which comprised hydrophilic interaction, weak anion-exchange, and electrophoresis. The influences of buffer concentration and organic modifier content on the separation of nucleotides by pCEC have been investigated. In addition, the monolithic silica columns were also able to separate various polar compounds such as phenols, nucleic acid bases, and nucleosides in the hydrophilic interaction CEC mode.

An isocratic elution pressurized CEC (pCEC) system was used to separate and determine ten carbamate insecticides. It was found that introduction of the electrical field, supplementary pressure, and SDS in the proposed method greatly improved the speed, column efficiency, selectivity, and repeatability for separation and determination of carbamates. On a capillary column of 75 microm ID packed with 3 microm octadecyl silica, baseline separation and detection of ten analytes was performed by using a mobile phase consisting of 30% v/v ACN and 70% v/v of 5 mmol/L ammonium acetate (pH 6.5) containing 1 mmol/L SDS and 0.01% triethylamine (TEA). Under the optimum conditions ten carbamate insecticides could be completely separated within 20 min. For the real vegetable samples, an SPE procedure for the cleanup of matrices was carried out prior to pCEC analysis. The detection limits of 0.05-1.6 mg/kg for ten carbamates and mean recoveries of 51.3-109.2% for eight kinds of vegetable samples at different concentrations of carbamates with RSD less than 11.4% were obtained, respectively. The proposed method has been proved to be effective in the rapid analysis of carbamate residues in vegetables.

In this paper, pressurized CEC was used for the separation and determination of seven fluoroquinolones (FQs). The effect of different experimental conditions, such as the concentration and pH of the buffer, the organic modifier concentration, the surfactant and ion-paring agents added to the electrolyte, and applied voltage were studied. All the seven FQs were baseline separated using mobile phase containing 27% v/v ACN, 5 mmol/L Na2HPO4 buffer (pH 4.0 adjusted using citric acid), 11 mmol/L SDS, and 0.01% TEA v/v at detection wavelength of 287 nm and at an applied voltage of -10 kV. The calibration curves were linear (r>0.9991) over a concentration range of 1.0-50.0 mg/L for norfloxacin (NFLX); 2.5-50.0 mg/L for fleroxacin (FLX), ciprofloxacin (CPFX), and lomefloxacin (LMX); and 5.0-50.0 mg/L for enoxacin (ENX), ofloxacin (OFLX), and gatifloxacin (GFLX). The detection limits (S/N = 3) for ENX, OFLX, FLX, NFLX, CPFX, LMX, and GFLX were 0.5, 0.8, 0.4, 0.2, 0.4, 0.5, and 1.0 mg/L, respectively. The method is simple, rapid, and reproducible. It was successfully applied to the analysis of fish muscle samples spiked with FQs. Mean recoveries ranged from 81.6 to 97.6%.

Enrofloxacin (ENR) and its metabolite ciprofloxacin (CIP) were determined by capillary zone electrophoresis (CZE) with end-column amperometric detection. The effect of several factors, such as pH and concentration of running buffer solution, separation voltage, injection time, and working potential, on CZE were investigated to establish the optimal conditions of separation and detection. Under a given set of conditions (pH 8.00 phosphate buffer solution (20 mmol/L); +0.95 V for the working potential; 18 kV for the separation voltage; sample injection at 18 kV for 10 s), the compounds investigated can be well separated and detected within 8 min. Excellent linearity was observed between peak currents and concentration of analytes in the range from 0.034 to 70.0 mg/kg for these two compounds. The detection limits (S/N= 3) for enrofloxacin and ciprofloxacin were 13.68 mg/kg and 14.35 mg/kg, respectively, which were about 7-fold lower than the maximum residue limits (MRLs) established by the European Union. A simple sample pretreatment method was developed and proved to be effective in obtaining good recoveries and short analysis time. The developed CE-AD method was simpler, faster, and less cost intensive than other reported methods, and allows the determination of ENR and its metabolite CIP in contaminated eel liver samples and other animal tissue samples at the required maximum residue limits.

An improved technique, pressurized capillary electrochromatography (pCEC) coupling with end-column amperometric detection (AD), was developed and used for the separation and determination of estrogens. The effects of pH value, composition of mobile phase, concentration of the surfactant sodium dodecyl sulfate (SDS) and applied voltage on separation were investigated. The electrochemical oxidation of diethylstilbestrol (DES), dienestrol (DE), and hexestrol (HEX) could be reliably monitored with a carbon electrode at 0.9 V (vs. Ag/AgCl). The pCEC analyses were performed on a capillary separation column packed with 3 microm C18 particles with an acetonitrile/water (31%: 69%) mobile phase containing Tris buffer (5 mmol/L, pH 4.5) and 4 mmol/L SDS. High voltage up to 12 kV reduced the retention time dramatically and still provided a baseline resolution. In addition, supplementary pressure prevented bubble formation and provided reliability and reproducibility of the pCEC performance. The detection limits for the three estrogens ranged from 1.2 to 2.2x10(-7) mol/L, about 10 20-fold lower than those obtained with pCEC-UV detection. To evaluate the feasibility and reliability of this system, the proposed pCEC-AD method was further demonstrated with fish muscle samples spiked with estrogens.