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ABSTRACT: β-cyclodextrin modified gold nanoparticles (CD-GNP) were employed as the stationary phase in monolith capillary electrochromatography (CEC) to facilitate enantioseparation. CD-GNP were covalently bound to the surface of the thiolated porous polymer monolithic column. The fabricated enantioselective monolithic column was characterized by a variety of spectroscopic methods. The column exhibited steady EOF mobility over pH values ranging from 4.6 to 9.7. Additionally, the column was stable under CEC separation conditions over 180min. Moreover, the column exhibited good column-to-column reproducibility. The CD-GNP-modified monolithic column was employed in the efficient CEC separation of three pairs of drug enantiomers (chlorpheniramine, zopiclone and tropicamide). The results exhibit reproducible run-to-run enantioseparations and the monolith column can maintain its enantioselectivity for more than 1 month if the column is stored in a CD-GNP solution at 4°C.
Talanta 05/2013; 109:1-6. · 3.79 Impact Factor
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ABSTRACT: We reported the application of graphene as a novel stationary phase in open-tubular capillary electrochromatography (OTCEC). The OT column was easily fabricated by electrostatic assembly of poly(diallydimethylammonium chloride) followed by self-adsorption of negatively charged graphene. The chromatographic properties of graphene-coated OT column were investigated by separation of nitroaniline isomers through variation of the buffer pH, sodium dodecyl sulfate concentration and separation voltage. The results demonstrate the application of graphene in OTCEC greatly improves the separation by largely enhancing the surface area thus increasing stationary/mobile phase interaction. The proposed OT column exhibits good repeatability with run-to-run RSD of retention time as low as 1.5% (n=5), and excellent stability for at least two-week usage with total ∼200runs. The method was successfully applied for analysis of nitroaniline isomers in hair dye samples.
Journal of chromatography. A 01/2013; · 4.19 Impact Factor
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ABSTRACT: A novel replaceable dual-enzyme capillary microreactor was developed and evaluated using magnetic fields to immobilize the alcohol dehydrogenase (ADH)- and lactate dehydrogenase (LDH)-coated magnetic beads at desired positions in the capillary. The dual-enzyme assay was achieved by measuring the two consumption peaks of the coenzyme β-nicotinamide adenine dinucleotide (NADH), which were related to the ADH reaction and LDH reaction. The dual-enzyme capillary microreactor was constructed using magnetic beads without any modification of the inner surface of the capillary, and showed great stability and reproducibility. The electrophoretic resolution for different analytes can be easily controlled by altering the relative distance of different enzyme-coated magnetic beads. The apparent K(m) values for acetaldehyde with ADH-catalyzed reaction and for pyruvate with LDH-catalyzed reaction were determined. The detection limits for acetaldehyde and pyruvate determination are 0.01 and 0.016 mM (S/N = 3), respectively. The proposed method was successfully applied to simultaneously determine the acetaldehyde and pyruvate contents in beer samples. The results indicated that combing magnetic beads with CE is of great value to perform replaceable and controllable multienzyme capillary microreactor for investigation of a series of enzyme reactions and determination of multisubstrates.
Electrophoresis 07/2012; 33(14):2145-51. · 3.30 Impact Factor
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ABSTRACT: We proposed the first application of an electrophoretically mediated microanalysis (EMMA) method for fast online discrimination and determination of substrate enantiomers, which was achieved by just one EMMA assay. Lactate dehydrogenase (LDH)-catalyzed reaction was studied to evaluate the feasibility and performance of the presented method. The L- and D-LDH chiral enzymatic reactions, which are highly stereoselective to the lactate enantiomers, were initiated successively in one capillary, and the corresponding products, nicotinamide adenine dinucleotide (NADH), were online discriminated and detected by UV absorption. Excellent linear dependence of the two NADH peak intensities on the concentration of the corresponding lactate enantiomers was obtained within a wide range of 0.1-10 mM. The limit of detection was 26 μM for D-lactate and 49 μM for L-lactate (S/N = 3). Good repeatability of online chiral discrimination was demonstrated with relative standard deviation (RSD) < 6.3% for NADH peak height and RSD < 1.5% for migration time (n = 5). K(m) values for L- and D-lactate were measured and were consistent with those of the off-line enzyme assays. The presented method was successfully applied to determine the L-/D-lactate in several yogurt and wine samples. Our study shows a new application of the EMMA method utilizing high stereoselectivity of enzymes for fast online chiral analysis.
Analytical Chemistry 06/2012; 84(15):6701-6. · 5.86 Impact Factor
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ABSTRACT: The potential application of ordered mesoporous carbon (OMC)-modified glassy carbon electrode (OMC/GCE) in electrochemistry
as a novel electrode material was investigated. X-ray diffraction, transmission electron micrographs, and cyclic voltammetry
were used to characterize the structure and electrochemical behaviors of this material. Compared to GC electrode, the peak
currents of potassium ferricyanide (K3[Fe(CN)6]) increase and the peak potential separation (ΔE
p) decreases at the OMC/GC electrode. These phenomena suggest that OMC-modified GC electrode possesses larger electrode area
and faster electron transfer rate, as compared with bare GC electrode. Furthermore, riboflavin was detected using OMC/GC electrode
in aqueous solutions. The results showed that, under an optimum condition (pH7.0), the OMC/GC electrode exhibited excellent
response performance to riboflavin in the concentration range of 4.0 × 10−7 to 1.0 × 10−6M with a high sensitivity of 769µAmM−1. The detection limit was down to around 2 × 10−8M. With good stability and reproducibility, the present OMC/GC electrode was applied in the determination of vitamin B2 content in vitamin tablets, and satisfactory results were obtained.
KeywordsOrdered mesoporous carbon-Riboflavin-Vitamin B2
-Cyclic voltammetry
Journal of Solid State Electrochemistry 04/2012; 14(12):2251-2256. · 2.13 Impact Factor
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ABSTRACT: We have developed an easy-to-operate and effective method for performing the sequential online analysis of enzyme reactions based on capillary electrophoresis (CE). The system was constructed by passing two capillaries through a sample vial at a distance of 5 μm between the capillary ends. Direct online sample injection and sequential CE analysis were achieved by periodically switching the high-voltage power supply off and on, without any physical disturbance of the capillary inlet. The sample was injected via concentration diffusion with in-column derivatization of the amino acids occurring at the interface of the capillaries. High reproducibility of the sequential injections was demonstrated with relative standard deviation values (n = 20) of 1.01%, 1.25%, and 0.80% for peak height, peak area, and migration time, respectively. Sequential online CE enzyme assay of a glutamate pyruvate transaminase catalyzed enzyme reaction was carried out by simultaneously monitoring the substrate consumption and the product formation every 30 s from the beginning to the end of the reaction. The Michaelis constants for the reaction were obtained and were found to be in good agreement with the results of traditional off-line enzyme assays. Our method has great potential for usage in sequential online CE analysis of chemical reactions with in-column chemical derivatization of the analytes for ultraviolet or laser-induced fluorescence detection.
Analytical Chemistry 03/2012; 84(6):2961-7. · 5.86 Impact Factor
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ABSTRACT: Enantioselective open-tubular CEC (OTCEC) with thiolated β-CD modified gold nanoparticles (CD-GNPs) as stationary phase was developed. The enantioselective OT capillary column was fabricated by electrostatic assembly of poly(diallydimethylammonium chloride) (PDDA) followed by self-adsorption of negatively charged CD-GNPs. The enantioselective capillary column has a steady EOF mobility over a wide pH range of 3.0 to 9.2 (RSD 4.8%), and is quite stable over 240 min with very good column to column reproducibility. Efficient enantioseparation of the presented method was demonstrated by analyzing three drug enantiomers. Our results show that the column exhibits good run-to-run repeatability for enantioseparations and can maintain the enantioselectivity for more than 1 month if the column was stored in CD-GNPs solution at 4 °C.
Journal of chromatography. A 06/2011; 1218(23):3725-9. · 4.19 Impact Factor
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ABSTRACT: A novel method for monitoring of enzyme reaction and inhibition with high temporal resolution was developed by using optically gated vacancy capillary electrophoresis (OGVCE) with laser-induced fluorescence (LIF) detection and immobilized enzyme. Trypsin cleavage reaction and inhibition were investigated by the presented OGVCE-LIF assay, using carboxyfluorescein (FAM) end-labeled Angiotensin as the substrate and commercially available immobilized trypsin. The substrate and the product were continuously loaded into the capillary by the electroosmotic flow while the immobilized enzyme remained in the sample vial. Substrate consumption and product formation were monitored simultaneously at 5s interval during the whole reaction time. The enzymatic reaction rates obtained from the substrate and the product were highly consistent. The enzyme activity and the Michaelis constants of trypsin cleavage reaction, as well as the inhibition constant (for reversible competitive inhibitor) and the inhibition fraction (for irreversible inhibitor), were obtained. It was showed that the reported OGVCE-LIF method can perform fast, accurate, sensitive and reproducible CE enzyme assay with high temporal resolution, thus has great potential in application of the enzyme-substrate systems with fast reaction rate and the fluorescent substrate and products.
Analytica chimica acta 12/2010; 683(1):136-42. · 4.31 Impact Factor
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ABSTRACT: The application of chemical-modified gold nanoparticles (GNPs) as chiral selector for the enantioseparation based on pseudostationary phase-CEC (PSP-CEC) is presented. GNPs modified by thiolated beta-CD were characterized by NMR and FT-IR. The nanoparticle size was determined to be of 9.5 nm (+2.5 nm) by Transmission Electron Microscopy (TEM) and UV spectra. Four pairs of dinitrophenyl-labeled amino acid enantiomers (DL-Val, Leu, Glu and Asp) and three pairs of drug enantiomers (RS-chlorpheniramine, zopiclone and carvedilol) were analyzed by using modified GNPs as the chiral selector in PSP-CEC. Good theoretical plate number (up to 2.4x10(5) per meter) and separation resolution (up to 4.7) were obtained even with low concentration of modified GNPs (0.8-1.4 mg/mL). The corresponding concentration of beta-CD in the buffer was only 0.30-0.53 mM, which was much lower than the optimum concentration of 15 mM if pure beta-CD was used as chiral selector. Our results showed that thiolated beta-CD modified GNPs have more sufficient interaction with the analytes, resulting in significant enhancement of enantioseparation. The study shed light on potential usage of chemical modified GNPs as chiral selector for enantioseparation based on PSP-CEC.
Electrophoresis 05/2010; 31(10):1697-705. · 3.30 Impact Factor
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ABSTRACT: A new method for high-sensitive determination of glutamate was developed and evaluated based on CE by using dual-enzyme co-immobilized capillary microreactor combined with substrate recycling. The capillary microreactor was prepared by covalently co-immobilizing glutamate dehydrogenase (GDH) and glutamic pyruvic transaminase (GPT) on the inner surface of a capillary and was characterized by SEM, ultraviolet-visible spectroscopy, and fluorescence spectroscopy. The GDH-GPT co-immobilized capillary microreactor showed great stability and reproducibility. The apparent K(m) for glutamate with GDH-GPT coupled reaction was determined to be 0.61+/-0.06 mM but 2.56+/-0.24 mM when only GDH was immobilized. Glutamate determination was based on on-column monitoring UV absorption at 340 nm of the reaction product reduced nicotinamide adenine dinucleotide, of which peak area was directly related to the glutamate concentration. The response of the present co-immobilized GDH-GPT assay for glutamate is greatly enhanced over single enzyme system, and a 15.7-fold improvement in sensitivity was obtained. The detection limit of the proposed method is 0.15 muM glutamate (S/N=3). Selectivity for glutamate is good over most of the 20 amino acids. Finally, this method was successfully applied to determine the glutamate content in rat plasma and serum samples.
Electrophoresis 10/2009; 30(20):3527-33. · 3.30 Impact Factor
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ABSTRACT: A novel open-tubular capillary electrochromatography (OTCEC) column was prepared by immobilizing dodecanethiol gold nanoparticles on prederivatised fused-silica capillary columns with sol-gel technology. 3-Mercaptopropyl-trimethoxysilane (MPTMS) was selected as sol-gel precursor to develop a sol-gel layer on the inner wall of the capillary, prior to assembly of dodecanethiol gold nanoparticles onto the generated sol-gel layer through specific interaction between the gold nanoparticles and surface terminating thiol groups. The electrochromatographic behaviour of the sol-gel gold nanoparticle capillary was compared with a gold nanoparticle capillary prepared via MPTMS surface functionalisation, through variation of the percentage of the organic modifier, pH, and separation voltage. Efficient separation for a "reversed-phase" test mixture of thiourea, naphthalene, and biphenyl and for selected polycyclic aromatic hydrocarbons (PAHs) was obtained on the sol-gel based gold nanoparticle capillaries. OTCEC separations of three selected drug substances (propiophenone, benzoin, and warfarin) were also demonstrated. Scanning electron microscopy was used for the characterization of the sol-gel gold nanoparticle capillary surface. The results confirm that dodecanethiol gold nanoparticles, bound on the sol-gel-based inner layer of fused-silica capillary, can provide sufficient solute-bonded phase interactions for OTCEC with reproducible retention as well as characteristic reversed-phase behaviour.
Journal of Separation Science 06/2005; 28(8):757-66. · 2.73 Impact Factor
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ABSTRACT: The use of gold nanoparticles in conjunction with etched capillary-based open-tubular capillary electrochromatography (OTCEC) to improve the efficiency of separation and the selectivity between selected solutes is described. The fused-silica capillaries (50-microm i.d.) were etched with ammonium hydrogen difluoride, followed by prederivatization of the new surface with (3-mercaptopropyl)trimethoxysilane (MPTMS) for the immobilization of dodecanethiol gold nanoparticles, for OTCEC. The electrochromatography of a "reversed-phase" test mixture and of selected polycylic aromatic hydrocarbons was investigated, and efficient separations and high theoretical plate numbers per meter were obtained. The electroosmotic flow characteristics of the etched gold nanoparticle capillary, unetched gold nanoparticle capillary, bare capillary, and etched bare capillary were studied by varying the percentage of organic modifier in buffer, buffer pH, and separation voltage. Optical microscopy and scanning electron microscopy were used to examine the process of etching and modification and the surface features of the etched gold nanoparticle capillary. The results confirm that dodecanethiol gold nanoparticles bonded on the etched inner wall of the fused-silica capillary can provide sufficient solute-bonded phase interactions to obtain OTCEC separations with reproducible retention, as well as characteristic reversed-phase behavior, even with the inner diameter of the capillary of 50 microm.
Analytical Chemistry 04/2005; 77(6):1840-6. · 5.86 Impact Factor
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ABSTRACT: Ordered mesoporous carbon (OMC) functionalized with poly-azure B (denoted as PAB/OMC) composite-modified electrode was fabricated by electropolymerizing azure B (AB) on the surface of glassy carbon electrode (GCE). OMC provides a conductive network for the polymer immobilization. The new nanocomposite film was characterized by cyclic voltammetry (CV) and scanning electron microscopy (SEM). The results indicated that this poly nanocomposite modified electrode had strong electrocatalytic activity toward the oxidation of dihydronicotinamide adenine dinucleotide (NADH). NADH could effectively accumulate on the modified electrode and generate a sensitive anodic peak at 0.045 V (vs. Ag/AgCl) in pH 7.0 phosphate buffer solution. Under the selected conditions, the anodic peak current of NADH was linear with its concentration within the range from 3.0 to 1000 μM, and the detection limit was 0.1 μM (S/N = 3). The low detection potential of the nanocomposite film (0.045 V) also eliminated interferences from other redox-active molecules such as uric acid (UA), dopamine (DA) and ascorbic acid (AA). In comparison with the OMC/GCE or PAB/GCE electrode prepared in the similar way, this composite-modified electrode exhibited better catalytic activity, selectivity and linear range.
Journal of Electroanalytical Chemistry. 643:52-57.
