[Show abstract][Hide abstract] ABSTRACT: Graphite and graphene electrodes were prepared by using pure graphite as precursor. The electrode materials were characterized by a scanning electron microscope (SEM), X-ray diffraction (XRD) and cyclic voltammetry (CV) measurements. The electro-catalytic activity for degradation of sulfisoxazole (SIZ) was investigated by using prepared graphene or graphite anode. The results showed that the degradation of SIZ was much more rapid on the graphene than that on the graphite electrode. Moreover, the graphene electrode exhibited good stability and recyclability. The analysis on the intermediate products and the measurement of active species during the SIZ degradation demonstrated that indirect oxidation is the dominant mechanism, involving the electro-catalytic generation of OH and O2− as the main active oxygen species. This study implies that graphene is a promising potential electrode material for long-term application to electro-catalytic degradation of organic pollutants.
[Show abstract][Hide abstract] ABSTRACT: Ciprofloxacin (CIP) in natural waters has caused serious environmental problems because of its potent biological activity. In this study, the visible light-induced degradation of CIP was examined by using bismuth oxybromide (BiOBr) as photocatalyst. The flake-shape BiOBr was synthesized by hydrothermal method and characterized by X-ray powder diffraction, scanning electron microscopy and UV–vis diffuse reflectance spectroscopy. The degradation process was monitored by high performance liquid chromatography. The photodegraded intermediates were identified by high performance liquid chromatography–mass spectrometry and the degradation pathway was proposed on the basis of product analysis. It was found that, during the visible light induced degradation of CIP on BiOBr, the piperazine moiety of CIP was the predominant reaction sites, while the quinolone and cyclopropane rings remained essentially intact. The pH-dependence of reaction rates, product analysis and theoretical calculation pointed to a surface reaction mechanism that the CIP oxidation is dominant by the direct hole oxidation process, whereas OH, which is the common active species in the advance oxidation processes, is not effective in the visible light induced photocatalytic process on BiOBr. This study demonstrated that CIP is a good model substrate to uncover the photodegradation mechanism for photocatalyst whose valence band has moderate oxidation ability.
No preview · Article · Aug 2015 · The Chemical Engineering Journal
[Show abstract][Hide abstract] ABSTRACT: Hydrophilic interaction chromatography (HILIC) is a valuable alternative to reversed phase liquid chromatography (RPLC) for the analysis of highly polar and hydrophilic compounds, in which the separation mechanism is quite different from RPLC and the separation selectivity is complementary to RPLC. This separation mode can be characterized as normal phase liquid chromatography (NPLC) on polar columns in aqueous-organic mobile phases rich in organic solvents (usually acetonitrile). Silica has been the earliest developed and most widely used HILIC stationary phase. This review deals with the recent advances in the development of the retention mechanism on silica column with special attention to the effects of stationary phase, mobile phase composition and temperature on separation in HILIC mode. Moreover, the developing trends and applications of this HILIC mode are presented.
No preview · Article · Jul 2014 · Se pu = Chinese journal of chromatography / Zhongguo hua xue hui
[Show abstract][Hide abstract] ABSTRACT: A rapid method based on hydrophilic interaction chromatography (HILIC) using UV detection was developed for analysis of diazepam and estazolam in human plasma. The method utilized a Kromasil KR100-5SIL column (250 mm × 4.6 mm I.D., 5 µm) with a mobile phase consisting of acetonitrile-sodium formate buffer (10 mM, pH = 5.5) (90:10, v/v) at a flow rate of 1.0 mL/min. The detection wavelength was 254 nm. The chromatographic run time was less than 5 min per injection. All the experiments were performed at room temperature. The isolation of the analytes from plasma samples was achieved by solid phase extraction (SPE) using Oasis HLB cartridges. The standard curve range was 25–5000 ng/mL (r2 > 0.99) for diazepam and estazolam using 0.2 mL of human plasma. The limit of quantification (LOQ) and limit of detection (LOD) for both compounds were 25 and 10 ng/mL, respectively. Recoveries of the analytes ranging from 70.7% to 88.5% with intra- and inter-day precision (RSD) less than 11% were obtained at the concentrations above the LOQ. The proposed method is rapid, simple, accurate, and its mobile phase is compatible for mass spectrometry, proving an alternative method for benzodiazepine drug monitoring in forensic and clinical toxicology as well as pharmacokinetic studies.
No preview · Article · Mar 2013 · Journal of Liquid Chromatography & Related Technologies
[Show abstract][Hide abstract] ABSTRACT: Hemicelluloses represent a large reservoir of carbohydrates that can be utilized for renewable products. Hydrolysis of hemicellulose into simple sugars is inhibited by its various chemical substituents. The glucuronic acid substituent is removed by the enzyme α-glucuronidase. A gene (deg75-AG) encoding a putative α-glucuronidase enzyme was isolated from a culture of mixed compost microorganisms. The gene was subcloned into a prokaryotic vector, and the enzyme was overexpressed and biochemically characterized. The DEG75-AG enzyme had optimum activity at 45 °C. Unlike other α-glucuronidases, the DEG75-AG had a more basic pH optimum of 7-8. When birchwood xylan was used as substrate, the addition of DEG75-AG increased hydrolysis twofold relative to xylanase alone.
No preview · Article · Apr 2012 · Journal of Industrial Microbiology
[Show abstract][Hide abstract] ABSTRACT: Hydrophilic interaction chromatography (HILIC) has been used as a supplement method of reversed-phase liquid chromatography (RPLC) for the separation of the polar and hydrophilic compounds, and has been received more and more attention in recent years. One reason is that the separation problems of strongly polar compounds are rising in various fields. Another is that there are some obvious advantages of HILIC compared with RPLC in the separation of polar compounds, such as low viscosity of mobile phase, good permeability of the column, high sensitivity when coupled to mass spectrometry and low back pressure. In this review, the development history, characteristics and retention mechanism of HILIC are summarized. The main attention in this review is on the applications of HILIC in environmental analysis. In addition, the advantages and disadvantages of HILIC and RPLC in the separation of pollutants are discussed, and the development trends of HILIC applications in environmental analysis are proposed.
No preview · Article · Mar 2012 · Se pu = Chinese journal of chromatography / Zhongguo hua xue hui
[Show abstract][Hide abstract] ABSTRACT: α-Glucuronidase enzymes play an essential role in the full enzymatic hydrolysis of hemicellulose. Up to this point, all genes encoding α-glucuronidase enzymes have been cloned from individual, pure culture strains. Using a high-throughput screening strategy, we have isolated the first α-glucuronidase gene (rum630-AG) from a mixed population of microorganisms. The gene was subcloned into a prokaryotic vector, and the enzyme was overexpressed and biochemically characterized. The RUM630-AG enzyme had optimum activity at pH 6.5 and 40 °C. When birchwood xylan was used as substrate, the RUM630-AG functioned synergistically with an endoxylanase enzyme to hydrolyze the substrate.
No preview · Article · Feb 2012 · The Protein Journal
[Show abstract][Hide abstract] ABSTRACT: Hydrophilic interaction chromatography (HILIC) has emerged as a viable option for many applications dealing with polar and hydrophilic analytes. The application of HILIC for the analysis of environmental samples has increased in the last years. Solid-phase extraction (SPE) coupled with HILIC-UV or MS (MS/MS) or ICP/MS has been utilized to pretreat, separate, and detect the residuals of numerous contaminants (pesticides, pharmaceuticals, drugs of abuse, free estrogens and their conjugates, aromatic amines, surfactants, metal complexes, etc.) in the environmental matrices. This article reviews the recent applications of this chromatographic technique in the environmental analysis. This review also presents a compilation of other reviews on HILIC.
No preview · Article · Aug 2011 · Journal of Liquid Chromatography & Related Technologies
[Show abstract][Hide abstract] ABSTRACT: Effects of mobile-phase variations on the chromatographic separation on amino-bonded silica column in hydrophilic interaction chromatography (HILIC) were investigated for four zwitterionic tetracyclines (TCs): oxytetracycline, doxycycline, chlortetracycline, and tetracycline. A mixed-mode retention mechanism composed of partitioning, adsorption, and ion exchange interactions was proposed for the amino HILIC retention process. Buffer type and pH significantly influenced the retention of TCs, but showed similar separation selectivity for the tested analytes. Experiments varying buffer salt concentration and pH demonstrated the presence of ion exchange interactions in TCs retention. The type and concentration of organic modifier also affected the retention and selectivity of the analytes, providing direct evidence supporting the Alpert retention model for HILIC. The retention time of the analytes increased in the following order of organic modifiers: tetrahydrofuran < methanol < isopropanol < acetonitrile. The linear relationships of logk' versus %water (v/v) curve and logk' versus logarithm of %water (v/v) in the mobile phase indicated that TCs separation on the amino phase was controlled by partitioning and adsorption. The developed method was successfully utilized in the detection of TCs in both river water and wastewater samples using solid-phase extraction (SPE) for sample cleanup.
No preview · Article · Jul 2011 · Journal of Separation Science
[Show abstract][Hide abstract] ABSTRACT: In the present study, a simple, sensitive, and rapid hydrophilic interaction chromatographic (HILIC) method with ultraviolet (UV) detection for the analysis of oxytetracycline (OTC) was developed and applied to the determination of the antibiotic in environmental waters. OTC was extracted and purified from water samples by solid-phase extraction (SPE) employing Oasis HLB cartridge and analyzed on a Kromasil silica column with the mobile phase of acetonitrile-sodium oxalate (10 mM, pH 2.5) (90:10, v/v). The analyte was detected at 365 nm, and the total analysis time was 7 min. Method validation was accomplished by examination of the linearity, precision, accuracy, limit of detection (LOD), and limit of quantification (LOQ). More importantly, in a linear range of 0.15–10 mg L−1, OTC had high repeatability with good peak shape and no irreversible adsorption was found. The results of this study demonstrated that bare silica column could be used in the determination of tetracycline antibiotics in HILIC mode with no peak tailing, providing a different understanding from that previously found in literature.
No preview · Article · Apr 2011 · Journal of Liquid Chromatography & Related Technologies
[Show abstract][Hide abstract] ABSTRACT: N-doped nano-crystalline TiO2 powders have been synthesized by the sol-gel method. The shape and crystal structure of the resulting N-doped TiO2 were investigated by X-ray Photoelectron Spectroscopy (XPS), X-ray spectroscopy (XRD), Transmission Electron Microscopy (TEM)
and UV-vis reflection spectrum. The results showed that doping TiO2 with nitrogen can lower its band gap and apparently shift its optical response to the visible region. Under the visible light
(λ > 420 nm) irradiation, the MC-LR was degraded by the synthesized N-TiO2 nano-material. The variation of MC-LR amount and its intermediates were detected by high performance liquid chromatography
(HPLC) and LC-MS, respectively. The mineralization of MC-LR was determined by total organic carbon (TOC) analysis. Simultaneously,
transient oxidative species generated during photocatalysis were tracked by electron spin resonance (ESR) and Peroxidase method.
All these results indicated that visible-light excited N-TiO2 can activate molecular oxygen and thereby achieve degradation of MC-LR completely within 14 h. The removal of 59% of TOC
was achieved after 20 h irradiation. The major oxidative species in the system were hydroxyl radical (·OH) and H2O2. 13 Kinds of intermediates were primarily identified in the process. Based on these results, a reasonable conclusion was
drawn for the degradation of MC-LR wherein its four positions are easy to be attacked by the photo-generated OH radical followed
by the hydrolyzation of peptides.
Keywordsvisible Light-microcystin-LR-N-doped titanium dioxide-photocatalysis
No preview · Article · Aug 2010 · Science China-Chemistry
[Show abstract][Hide abstract] ABSTRACT: A simple, precise, and accurate hydrophilic interaction liquid chromatographic (HILIC) method has been developed for the determination of five aromatic amines in environmental water samples. Chromatography was carried out on a bare silica column, using a mixture of acetonitrile and a buffer of NaH(2)PO(4)-H(3)PO(4) (pH 1.5, containing 10mM NaH(2)PO(4)) (85:15, v/v) as a mobile phase at a flow rate of 1 mL min(-1). Aromatic amines were detected by UV absorbance at 254 nm. The linear range of amines was good (r(2)>0.998) and limit of detection (LOD) within 0.02-0.2 mg L(-1) (S/N=3). The retention mechanism for the analytes under the optimum conditions was determined to be a combination of adsorption, partition and ionic interactions. The proposed method was applied to the environmental water samples. Aromatic amines were isolated from aqueous samples using solid-phase extraction (SPE) with Oasis HLB cartridges. Recoveries of greater than 75% with precision (RSD) less than 12% were obtained at amine concentrations of 5-50 microg L(-1) from 100mL river water and influents from a wastewater treatment plant (WWTP). The present HILIC technique proved to be a viable method for the analysis of aromatic amines in the environmental water samples.
Full-text · Article · Mar 2010 · Journal of Chromatography A
[Show abstract][Hide abstract] ABSTRACT: The gene (manf-x10) encoding xylanase from an environmental genomic DNA library was cloned and expressed in Escherichia coli. The manf-x10 encoded a predicted protein of 467 amino acids residues with a molecular mass of 50.3kD. Sequence analysis of manf-x10 gene revealed that the N-terminus had high homology to the catalytic domain of other bacterial xylanase enzymes. The optimal
pH and temperature for xylanase activity were 7.0 and 40°C, respectively. In the presence of 1mM solution of Co2+, Fe2+, Mg2+ and Zn2+, the relative xylanase activity was enhanced; however, it had almost no activity in the presence of 10mM solution of Cu2+. The apparent K
m and V
max values obtained for the hydrolysis of rye arabinoxylan were 2.8mg/ml and 49.5μmol/min/mg, respectively. The C-terminus
of the enzyme had high homology to a domain of unknown function found in several mannanase enzymes. Biochemical characterization
of the C-terminus of the enzyme revealed a previously unrecognized carbohydrate binding module.
No preview · Article · Nov 2009 · World Journal of Microbiology and Biotechnology