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ABSTRACT: In this paper, open-tubular capillary column coated with graphene oxide (GO) was prepared through ionic adsorption of negatively charged GO nanosheets onto the capillary wall pre-modified with positively charged poly(diallydimethylammonium chloride) (PDDA). Thus prepared coating was very stable and could endure over 200 separations. The electroosmotic flow (EOF) characteristics of bare fused silica capillary column, PDDA coated column, and GO-PDDA coated column (GO-PDDA@column) were investigated by varying the percentage of methanol in buffer and the buffer pH value. The run-to-run, day-to-day, and column-to-column reproducibilities of EOF on GO-PDDA@column were satisfying with relative standard deviation values of less than 2% in all cases. The stationary phase displays a characteristic reversed-phase behavior. The GO-PDDA@column was also used to separate proteins in egg white. Both basic and acidic proteins were separated in a single run.
Journal of chromatography. A 03/2013; 1282:95-101. · 4.19 Impact Factor
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ABSTRACT: This is the first time to prepare protein-imprinted polymers with "pending templates". The polymers were synthesized in the presence of a real sample (chicken egg white), rather than any known commercial proteins. Compared with a simultaneously synthesized non-imprinted control polymer, the polymers show higher adsorption capacity for abundant components (as "pending templates") in the original sample. Chromatography experiments indicated that the columns made of the imprinted polymers could retain abundant species (imprinted) and separate them from those not imprinted. Thus the sample could be split into dimidiate subfractions with reduced complexities. "Pending template imprinting" suggests a new way to investigate molecular imprinting, especially to dissect, simplify and analyze complicated samples through a series of polymers just imprinted by the samples per se.
Electrophoresis 03/2013; · 3.30 Impact Factor
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ABSTRACT: The graphene oxide (GO) is carbon based material that has high surface area, high adsorption ability, and is stable at high temperature. In this work, the GO phase was prepared and used for gas chromatographic separation. GO nanosheets were covalently bonded onto the inner surface of fused silica capillary column using 3-aminopropyldiethoxymethyl silane as cross-linking agent. The prepared GO nanosheets were characterized with TEM and the GO coating was characterized with SEM. As a high performance stationary phase, GO provides not only a high surface area to increase the phase ratio but also rich functional groups for the formation of hydrophobicity, hydrogen bonding, and π-π electrostatic stacking interactions with volatile aromatic or unsaturated organic compounds. Thus, mixtures of a wide range of organic compounds including alcohols and aromatic compounds were well separated and an efficiency of 1990 theoretical plates per meter for anisole was obtained on GO coated 1.0m×200μm i.d. fused silica capillary column. The experimental results demonstrate that GO coated capillary columns are promising for gas chromatographic separation.
Analytica chimica acta 12/2012; 757:83-7. · 4.31 Impact Factor
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ABSTRACT: Graphene oxide (GO) nanosheets were immobilized onto the capillary wall using 3-aminopropyldiethoxymethyl silane as coupling agent. Graphene coated column (G@column) was fabricated by hydrazine reduction of GO modified column. Scanning electron microscopy (SEM) images provided visible evidence of the GO grafted on the capillary wall. Energy dispersive X-ray spectrometry (EDS) indicated the high coverage of the GO on the capillary wall. The G@column exhibited a pH-dependent electroosmotic flow (EOF) from anode to cathode in the pH range of 3-9 while the graphene oxide coated column (GO@column) showed a constant EOF. Both GO@column and G@column were evaluated for open-tubular capillary electrochromatography (OT-CEC). The GO@column was also evaluated for open-tubular capillary liquid chromatography (OT-CLC). Good separation of the tested neutral analytes on the GO@column was achieved on the basis of a typical reversed-phase behavior. On the contrary, G@column showed poor separation performance because of the strong π-π stacking and hydrophobic interactions between graphene and polyaromatic hydrocarbons. The high coverage of GO improved the column phase ratio which makes the GO@column promising for OT-CLC separation. Five of the major known proteins including three glycoisoforms of ovalbumin in chicken egg white were identified in a single run on the GO@column with phosphate buffer (5 mM, pH 7.0) and an applied voltage of 20 kV. The run-to-run, day-to-day, and column-to-column reproducibilities are evaluated by calculating the relative standard deviations (RSDs) of the EOF in OT-CEC and retention time of naphthalene in OT-CLC, respectively. These RSD values were found to be less than 3%.
Analytical Chemistry 09/2012; 84(20):8880-90. · 5.86 Impact Factor
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ABSTRACT: A rapid, low-cost, and highly sensitive analytical method to detect glyphosate and its major metabolite, aminomethylphosphonic
acid (AMPA), in water samples has been developed, involving a derivatization with a new labeling reagent, 4-methoxybenzenesulfonyl
fluoride, followed by reverse phase liquid chromatography with ultraviolet detection. The limits of detection of both of glyphosate
and AMPA in real water samples are 0.1μgL−1 with simple pre-concentration. This method has proven to be sensitive and reliable for determination of glyphosate and AMPA
in water samples.
KeywordsColumn liquid chromatography-Water analysis-Glyphosate and aminomethylphosphonic acid-4-Methoxybenzenesulfonyl fluoride
Chromatographia 04/2012; 72(7):679-686. · 1.20 Impact Factor
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ABSTRACT: This paper reports on a new strategy to coat fused silica capillaries through ionic adsorption of gold nanoparticles (AuNPs) on a polyelectrolyte multilayer (PEM) modified capillary wall. The coating was constructed in situ by alternating rinses with positively charged poly(diallydimethylammonium chloride), negatively charged poly(sodium-4-styrenesulfonate), and positively charged AuNPs. After self-assembly of n-octadecanethiol onto the surface of AuNPs, the modified capillary was investigated as a new medium for the separation of neutral analytes and proteins in open-tubular capillary electrochromatography (OT-CEC). The surface coverage of the capillary wall was increased using the high density of AuNPs which were dynamically capped with 4-dimethylaminopyridine (DMAP). The chromatographic performance of the column coated with positively charged AuNPs was remarkably improved compared with a column modified with negatively charged AuNPs. The coating was robust over more than 810 runs in this study and also showed high stability against 0.01 M NaOH, 0.01 M HCl, and electrolyte concentrations up to 70 mM. The run-to-run, day-to-day, and capillary-to-capillary reproducibilities of electroosmotic flow were satisfying with relative standard deviation values of less than 1% in all cases. The AuNP-coated PEM modified capillary column not only showed good performance for neutral analytes but also was suitable for the analysis of both basic and acidic proteins.
Journal of chromatography. A 10/2010; 1217(42):6588-94. · 4.19 Impact Factor
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ABSTRACT: A rapid, low-cost, high sensitive and quantitative method to detect valiolamine in a medium for microbial culture, involving derivatization with a new labeling reagent, 4-methoxybenzenesulfonyl fluoride (MOBS-F), followed by reverse-phase high-performance liquid chromatography with ultraviolet (UV) detection with simple operation procedure. 4-Methoxybenzenesulfonyl chloride (MOBS-Cl) and 2-nitrobenzenesulfonyl chloride (NBS-Cl) were compared with MOBS-F as novel reagents in this paper, and the MOBS-F was chosen as the most suitable derivatization reagent. The column was thermostatic at 35 degrees C, the mobile phase flow-rate was 1.0mL/min and the detection wavelength was 240nm. For a biological sample, the separation of the derivatives was achieved using a gradient mobile system. The elution program is 88% phosphate buffer (50mM; pH=3.0) and 12% methanol for 23min, then 70% of phosphate buffer and 30% methanol for another 15min and finally 88% of phosphate buffer and 12% of methanol for 5min to re-equilibrate the column. The optimized conditions of the derivatization were as follows: derivatization reaction temperature 30 degrees C; derivatization reaction pH value 11.0, reaction time 10min and MOBS-F concentration higher than 1.5mg/mL for standard solutions and higher than 5.0mg/mL for the biological sample. Calibration curves were linear in the range of 0.050-25microg/mL for the standard solutions and 1.0-75microg/mL for the biological sample. The sensitive analytical method is helpful to control the biotechnological process of voglibose production and product quality control.
Talanta 06/2010; 81(4-5):1613-8. · 3.79 Impact Factor
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ABSTRACT: Bare nonporous silica particles with diameter around 1 microm were prepared. A 20 cm section of a total length of 45 cm capillary (100 microm i. d.) was packed electrokinetically and the separation performance of basic compounds was investigated in the pressurized capillary electrochromatography (pCEC) system using 1 microm nonporous bare silica spheres as stationary phase and acetonitrile-water as mobile phase. The effects of the composition of the mobile phase, the concentration of the buffer, pH value, applied voltage and so on on the separation performance were investigated. The experimental results demonstrated that the bare silica column showed a typical reversed phase separation mechanism when it was used for separation of basic compounds. The separation performance changed slightly with changing buffer concentration. Since the degree of dissociation of the basic compounds depended greatly on the pH value, the interaction between the compounds and stationary phase changed with the changing of pH value, thereby changing the resolution of the compounds. The separation performance increased with the increase of applied voltage. A column efficiency of 35 000 for o-toluidine was obtained when a voltage of 1 kV was applied.
Se pu = Chinese journal of chromatography / Zhongguo hua xue hui 03/2010; 28(3):260-3.
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ABSTRACT: Nonporous monodispersed silica spheres of 1.3 microm were coated with gold nanoparticles (AuNPs) and subsequently coated with n-octadecanethiol. By transmission electron microscopy analysis, the average diameter of the AuNPs on the silica spheres was determined to be 12 nm. The chromatographic and electrochromatographic properties of self-assembled n-octadecanethiol AuNP-coated silica microspheres (C18-AuNPs-SiO2) were investigated using a group of nonpolar PAHs. The stationary phase appears to display a characteristic reversed-phase behavior. Higher separation efficiency and shorter separation times were obtained using pressurized CEC (pCEC) compared with capillary LC (CLC). A maximum column efficiency of about 2.5x10(5) plates per meter and less than 18 min separation time for benzene were obtained in pCEC while only 66 507 plates per meter and an analysis time of nearly 100 min were observed in CLC mode. A chemical stability test of the C18-AuNPs-SiO2 stationary phase under extremely high and low pH conditions demonstrated that it is stable at pH 12 and 1 for at least 60 h. The results confirm that C18-AuNPs-SiO2 possesses a high rigidity to withstand high packing pressures and can be used as a good stationary phase for CLC and pCEC.
Electrophoresis 01/2010; 31(3):556-62. · 3.30 Impact Factor
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ABSTRACT: Gold microspheres modified with octadecanethiol as chromatographic stationary phase were prepared. The particles were characterized by the scanning electron micrograph (SEM), Fourier transform infrared spectroscopy (FT-IR), elemental analysis and nitrogen adsorption analysis. The average diameter, the surface area and the average pore diameter were 3.5 microm, 49.0 m2/g and 5.0 nm, respectively. The IR spectra demonstrated that C18 was bonded to the surface of gold microspheres with the carbon content of 0.56%. Using these microspheres as stationary phase, a 19 cm section of a total length of 36 cm capillary (100 microm i. d.) was packed electrokinetically, and the evaluations in capillary liquid chromatography and pressurized capillary electrochromatography were performed. The mobile phases (80% methanol) with extreme pH values (pH 1.0 or pH 12.0) were used to flush the column for 140 h. In order to investigate the chemical stability of the column, the retention factors before and after flushing were calculated and compared based on the experimental results. There was no remarkable deterioration on the retention factors after flushing, which demonstrated the column was stable pounds were separated using capillary liquid chromatography to examine the retention behavior of the column, and over 50,000 theoretical plates per meter and acceptable symmetry peaks were obtained. The pressurized capillary electrochromatographic properties of the column were investigated using a separation of the mixture of aniline and benzoic acid, and the separation was obtained when a 5 kV positive or negative voltage was applied. The research work confirmed the feasibility of using the octadecanethiol modified gold microspheres as a novel stationary phase for capillary liquid chromatography and pressurized capillary electrochromatography.
Se pu = Chinese journal of chromatography / Zhongguo hua xue hui 07/2009; 27(4):431-5.
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ABSTRACT: Amidosulfonic acid was electropolymerized by cyclic voltammetry onto the surface of glassy carbon electrode (GCE) to fabricate the chemically modified electrode, which showed high stability, good selectivity and reproducibility for determination of isoniazid. The modified electrode showed an excellent electrocatalytical effect on the oxidation of isoniazid. Under the optimum conditions, there was a good linear relationship between anodic peak current and isoniazid concentration in the range of 5.0 x 10(-8)- 1.0 x 10(-5) M, and a detection limit of 1.0 x 10(-8) M (S/N = 3) was obtained after 120 s at the accumulation potential of - 0.2 V (vs. SCE). This developed method had been applied to the direct determination of isoniazid in injection and tablet samples with satisfactory results.
Bioelectrochemistry 07/2008; 73(1):37-42. · 3.76 Impact Factor
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ABSTRACT: Octadecylamine-capped gold nanoparticles (ODA-Au-NPs) were prepared and characterized by using UV-Vis adsorption spectrum, transmission electron chromatography (TEM), SEM, and FT-IR. A simple but robust hydrophobic coating was easily developed by flushing a capillary with a solution of ODA-Au-NPs, because the positive charges were carried by the nanoparticles which strongly adsorb to the negatively charged inner surface of a fused-silica capillary via electrostatic and hydrophobic interactions. The chromatographic characteristics of the coated capillary was investigated by varying the experimental parameters such as buffer pH, buffer concentration, and percentage of organic modifier in the mobile phase. The results show that (i) resolution between thiourea and naphthalene is almost the same when comparing the electrochromatograms obtained using pH 7 buffer as mobile phase after and before the capillary column was operated using pH 11 and 3 mobile phase; (ii) no significant changes in retention time and deterioration in peak efficiency were found after 60 runs of test aromatic mixtures; and (iii) column efficiency up to 189 000 theoretical plates/meter for testosterone was obtained. All of the results indicated that the coating could act as a stable stationary phase for open tubular CEC as well as for bioanalysis.
Electrophoresis 03/2008; 29(4):901-9. · 3.30 Impact Factor
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ABSTRACT: The electrochemical oxidation of L-cysteine (CySH) in presence of carbon nanotubes (CNTs) formed a composite film at a glassy carbon electrode (GCE) as a novel modifier for directly electroanalytical determination of terbinafine without sample pretreatment in biological fluid. The determination of terbinafine at the modified electrode with strongly accumulation was studied by differential pulse voltammetry (DPV). The peak current obtained at +1.156 V (vs. SCE) from DPV was linearly dependent on the terbinafine concentration in the range of 8.0 x 10(-8)-5.0 x 10(-5 )M in a B-R buffer solution (0.04 M, pH 1.81) with a correlation coefficient of 0.998. The detection limit (S/N=3) was 2.5 x 10(-8 )M. The low-cost modified electrode showed good sensitivity, selectivity, and stability. This developed method had been applied to the direct determination of terbinafine in human serum samples with satisfactory results. It is hopeful that the modified electrode will be applied for the medically clinical test and the pharmacokinetics in future.
Bioelectrochemistry 03/2008; 72(1):107-15. · 3.76 Impact Factor
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ABSTRACT: Poly(phenol red) (denoted as PPR) films were electrochemically synthesized on the surface of a glassy carbon electrode (GCE)
by cyclic voltammetry to obtain a chemically modified electrode (denoted as PPR-GCE). The growth mechanism of PPR films was
studied by attenuated total reflection spectroscopy. This PPR-GCE was used to develop a novel and reliable method for the
determination of trace Pb2+ by anodic stripping differential pulse voltammetry. At optimum conditions, the anodic peak exhibits a good linear concentration
dependence in the range from 5.0 × 10−9 to 5.0 × 10−7 mol L−1 (r = 0.9989). The detection limit is 2.0 × 10−9 mol L−1 (S/N = 3). The method was employed to determine trace levels of Pb2+ in industrial waste water samples.
Microchimica Acta 12/2007; 160(1):275-281. · 3.03 Impact Factor
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ABSTRACT: Recent advances in electrochemical detection techniques coupled with high-performance liquid chromatography (HPLC-ECD) in pharmaceutical and biomedical analysis are reviewed. ECD classification and modes including common amperometric, coulometric, conductimetric, and potentiometric detector, are outlined and the some typical examples of determinations in pharmaceutical and biomedical analysis are described. The electrochemical detection system can offer superior merits over other detectors commonly used with HPLC. These techniques have great potential owing to their prominent characteristics in high-throughput screening procedures of drugs in various matrices. Fundamental 67 references from last 5 years related with a field are cited in this review.
Combinatorial Chemistry & High Throughput Screening 09/2007; 10(7):547-54. · 1.78 Impact Factor
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ABSTRACT: Polycysteic acid based electrochemical oxidation of L-cysteine (CySH) and carbon nanotubes (CNTs) formed a composite thin film material at a glassy carbon electrode (GCE) that was used a novel modifier for electroanalytical determination of sinomenine which is used for rheumatoid arthritis treatment. The determination of sinomenine at the composite modified electrode was studied by differential pulse voltammetry (DPV). The peak current obtained at + 0.632 V (vs SCE) from DPV was linearly dependent on the sinomenine concentration in the range of 1.0 x 10(-7) to 6.0 x 10(-5) M in a B-R buffer solution (0.04 M, pH 1.81) with a correlation coefficient of 0.998. The detection limit (S/N = 3) was 5.0 x 10(-8) M. The electrochemical reaction mechanism of sinomenine was also discussed. This new method was then applied to the high-throughput determination of sinomenine in human serum samples with satisfactory results. This polycysteic acid/CNTs composite film may be considered to be a promising, low-cost, durable, and biocompatible material for the modification of sensors in applications to pharmaceutical and biomedical analysis.
Combinatorial Chemistry & High Throughput Screening 09/2007; 10(7):595-603. · 1.78 Impact Factor
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ABSTRACT: The effect of a divalent cation (Mg2+) and 3 monovalent cations (Na+, Li+, and K+) as buffer additives on the electroosmotic flow (EOF) was investigated in order to improve the separation performance of p-acetamidobenzenesulfonyl fluoride (PAABS-F) derivatives of 20 standard amino acids by micellar electrokinetic chromatography (MEKC). The EOF can be decreased with increasing concentration of cations with the order of cations as Mg2+>K+>Na+>Li+. However, it was found that the resolution cannot be improved easily using a buffer cation which is more capable of decreasing the EOF. Taking the migration time, resolution, and peak shape into account, Na+ is the best buffer additive, although the EOF decreased most using Mg2+. Using 20 mmol/L borate at pH 9.3 containing 140 mmol/L SDS and 20 mmol/L Na+ as electrolyte, 20 standard amino acids were successfully separated within 14 min.
Journal of Chromatography B 07/2007; 853(1-2):31-7. · 2.89 Impact Factor
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ABSTRACT: Capillary electrochromatography (CEC) has attracted increasing interests in recent years. It combines the advantages of high efficiency of capillary electrophoresis (CE) with high selectivity of high performance liquid chromatography (HPLC). CEC also has a double retention mechanism of both CE and HPLC and, therefore, is suitable for simultaneous separation and analysis of neutral and charged compounds. In this paper, the preparation methods for various types of capillary columns for electrochromatography are reviewed in detail and their advantages and disadvantages are discussed.
Se pu = Chinese journal of chromatography / Zhongguo hua xue hui 04/2007; 25(2):157-62.
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ABSTRACT: Cysteic acid based on electrochemical oxidation of L-cysteine (CySH) form a novel thin film material at a glassy carbon electrode (GCE) for electroanalytical determination of sinomenine. The determination of sinomenine at the modified electrode with strongly accumulation was studied by differential pulse voltammetry (DPV). The peak current obtained at + 0.650 V (vs. SCE) from DPV was linearly dependent on the sinomenine concentration in the range of 1.0 × 10-6 ~ 1.0 × 10-4 M in a B-R buffer solution (0.04 M, pH 1.81) with a correlation coefficient of 0.999. The detection limit (S/N = 3) was found to be 6.0 × 10-7 M. The low-cost modified electrode showed good sensitivity, selectivity, stability and had been applied to the determination of sinomenine in pharmaceutical formulations with satisfactory results. The electrochemical reaction mechanism of sinomenine was also discussed firstly.
International Journal of Electrochemical Science. 01/2007;
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ABSTRACT: An online preconcentration method based on electrostatic interaction between the analytes and inner surface of the capillary column was developed for the determination of zwitterionic analytes such as amino acids in CE coupled with a DAD. The amino acids possessed positive charges when they were dissolved in an acidic solvent. When they were injected into the column, they were attracted by the negatively charged inner surface of the fused-silica capillary column. An etched column was used to increase the area of the capillary's inner surface and, consequently increase the electrostatic interaction between the amino acids and the inner surface of the capillary column. It was found that when the sample was injected at 10 psi for 1 min and the pH value of the sample was 4, the amount of amino acids attracted to the inner surface of the capillary was maximum. Under these optimized experimental conditions, the detection sensitivity of CE-DAD was enhanced by 5200, 2800, and 3100 times for asparagine, tryptophan and phenylalanine, respectively, compared with normal CE separation. The method provided good reproducibility in terms of both migration time and peak height. It can be successfully used for the preconcentration zwitterion.
Electrophoresis 12/2006; 27(22):4500-7. · 3.30 Impact Factor
