Development and Validation of Nonaqueous Capillary Electrophoresis Method for Simultaneous Estimation of Icariin,Icariside II,and Epimedin K in Epimedium Leaves

This paper describes a novel nonaqueous capillary electrophoresis method for the separation and determination of Icariin, Icariside II, and Epimedin K in Epimedium leaves. Three flavonoids were extracted by ultrasonication with EtOH-H₂O (70:30) followed by a HP 20 resin column cleanup procedure. The optimized electrophoretic conditions were obtained with the running solution of 8 mM borate MeCN/H₂O (60:40, v/v) (pH 11.40), separation voltage of +20 kV and detection wavelength of 270 nm. The limits of quantification ranged from 0.24 to 0.84 mg/kg (signal/noise = 3) for three flavonoids. Three flavonoids in 10 Epimedium leaves were successfully measured and evaluated.     

Determination of Matrine and Oxymatrine in Sophora Flavescens by Nonaqueous Capillary Electrophoresis-Electrospray Ionization-Ion Trap-Mass Spectrometry

A simple, rapid, and sensitive nonaqueous capillary electrophoresis-electrospray ionization-ion trap-mass spectrometry (NACE-ESI-IT-MS) method was developed for determination of matrine and oxymatrine in Sophora Flavescens and medicinal preparations. The conditions for NACE separation and MS detection were systematically optimized. The optimum NACE buffer contained 30 mM ammonium acetate, 1% acetic acid, and 15% acetonitrile in methanol and the applied voltage on separation capillary was set at 25 kV. Berberine was selected as internal standard. In order to generate a stable electrospray, a sheath liquid (isopropanol/H₂O, 2/1, v/v) was used, which could also boost the flow through the ESI needle. The matrine and oxymatrine solutions were introduced into MS detection by a syringe pump for collecting the MSⁿ spectra to investigate the main fragment ions and its possible cleavage pathways. Both matrine and oxymatrine showed good linearity in the concentration ranges from 0.5 to 400 µg/mL, with linear correlation coefficient R > 0.99 and the limit of detections were 37.5 ng/mL for matrine and 50.0 ng/mL for oxymatrine, respectively. The recoveries at different content of Sophora Flavescens were 98.3%–102.9% for MT and 95.3%–100.6% for OMT, which indicates the reliability of this method.     

Rapid separation of basic drugs by nonaqueous capillary electrophoresis

Summary Nonaqueous capillary electrophoresis (NACE) has been used to achieve rapid separations of basic drugs. A high electric field was obtained by using short capillaries. Baseline separations of basic drugs, including amphetamines, tropane alkaloids and local anesthetics, were achieved in 1 min by selection of the appropriate organic solvent and electrolyte composition. Thus, high-throughput analyses can be performed. Peak efficiency up to 9154 theoretical plates s⁻¹ was achieved in a separation performed at 923V cm⁻¹. No discernible loss in resolution was observed when a conventional capillary (64.5cm) was replaced by a short (32.5 cm) capillary.     

非水体系中金电极表面增强拉曼光谱研究新进展

利用共焦显微拉曼系统,进行了甲醇溶液中硫氰酸根离子（SCN^-）在金电极上吸附行为的表面增强拉曼光谱（SERS）研究,结果表明：SCN^-与电极之间的相互作用非常强烈,在整个研究电位范围内都可以检测到其SERS信号。在－0．1～－0．6V区间内,SCN^-主要是以S端吸附在电极表面：而在－0．7V～－1．2V区间内,SCN^-主要是以N端吸附在电极表面。     

Inactivity of YGL082W in vitro due to impairment of conformational change in the catalytic center loop

MINDY-1 is a recently discovered new family of deubiquitinating enzymes(DUB),but one of its yeast homologs,YGL082 W,does not show any DUB activity in vitro.Sequence alignment shows that YGL082 W possesses the correct catalytic triad,and yet did not catalyze either the hydrolysis of di-ubiquitin,crosslinking with C-terminally propargylated ubiquitin,or hydrolysis of ubiquitin-7-amino-4-methylcoumarin.After obtaining a crystal structure of the catalytic domain of YGL082 W,we identified an interesting difference between the catalytic center loop of YGL082 W and that of its human homolog MINDY-1.Because the conformation of the catalytic center loop was previously reported to be important for the deubiquitination activity of MINDY-1,we hypothesized that Glu27(instead of the corresponding Pro136 in MINDY-1) of the catalytic center loop of YGL082 W may impair the conformational change and account for the lack of activity.This hypothesis was supported by homology modeling and molecular dynamics simulations,which showed that the Pro-to-Glu mutation(P136 E mutation for MINDY-1) creates a hydrogen bond that inhibits the conformation change of the catalytic center loop of MINDY-1.Further experiments through site-directed mutation validated this hypothesis,showing that the P27 E mutation caused MIY1(a homologous active DUB from yeast) to lose activity.     

Electron Transfer Kinetics of Ferrocene at Microcrystalline Boron‐Doped Diamond Electrodes: Effect of Solvent and Electrolyte

Cyclic voltammetric measurements were made using well‐characterized microcrystalline boron‐doped diamond thin‐film electrodes to test the material's responsiveness for ferrocene as a function of scan rate, solvent, and electrolyte composition. Apparent heterogeneous electron transfer rate constants, k°_app, of 0.042±0.015, 0.048±0.015, and 0.008±0.002 cm/s were observed in 0.1 M NaClO₄/CH₃CN, 0.1 M TBAClO₄/CH₃CN, and 0.1M TBAClO₄/CH₂Cl₂, respectively. These rate constants, obtained using electrodes without any type of pretreatment, are similar to those observed for freshly polished glassy carbon. The results demonstrate that boron‐doped diamond is a viable material for the electrochemical analysis of nonaqueous analytes.     

Development and Characterization of a Disposable Electrochemical Detector Arrangement for Capillary Electrophoresis Prepared by Thermal Lamination

A disposable electrochemical detector arrangement for capillary electrophoresis has been developed. The detection system consists of an assembly of a fused silica capillary and a microfiber electrode which are fixed in a proper position by sealing this configuration with the help of thermal lamination. The detector design is easy to prepare and inexpensive. Therefore it is used as a disposable device which can be replaced by a new one if any degradation of the performance characteristics occurs. The parameters influencing the detection performance were studied and optimized using nonaqueous capillary electrophoresis and ferrocene derivatives as model compounds. The practical utility was demonstrated by studying the separation and detection of water‐resistant dye compounds.     

Nonaqueous capillary electrophoresis method for the analysis of tamoxifen, imipramine and their main metabolites in urine

The viability of nonaqueous capillary electrophoresis (NACE) was investigated for the simultaneous determination of tamoxifen, imipramine and their main metabolites (4-hydroxytamoxifen and desipramine, respectively). Baseline separation of the studied solutes was obtained on a 57 cm × 75 μm capillary using a nonaqueous solution composed of 17 mM ammonium acetate and 1.25% acetic acid in 80:20 (v:v) methanol-acetonitrile, temperature and voltage 22 °C and 15 kV, respectively, and hydrodynamic injection. Paroxetine was used as internal standard. Different aspects including linearity, accuracy, ruggedness and precision was studied. Detection limits between 9.0 and 15.0 μg L⁻¹ were obtained for all the studied compounds. The developed method is simple, rapid and sensitive and has been used to determine tamoxifen, imipramine and their metabolites at clinically relevant levels in human urine. Before NACE determination, a solid phase extraction (SPE) procedure with a C₁₈ cartridge was necessary. Real determination of these analytes in three females urines were done.     

Nonaqueous capillary electrophoresis using a titania-coated capillary

In this work, an ordered mesoporous titania film was introduced to coat a capillary by means of the sol-gel technique. Its electroosmotic flow (EOF) property was investigated in a variety of nonaqueous media (methanol, formamide and N,N'-dimethylformamide and mixtures of methanol and acetonitrile). The titania-coated capillary exhibited a distinctive EOF behavior, the direction and magnitude of which were strongly dependent on various parameters such as the solvent composition, apparent pH (pH*) and the electrolytes. The nonaqueous capillary electrophoresis separation of several alkaloids was investigated in the positively charged titania-coated capillary. Comparison of separation between coated and uncoated capillaries under optimal nonaqueous conditions was also carried out.     

Peptide separations and dissociation constants in nonaqueous capillary electrophoresis: comparison of methanol and aqueous buffers

Nonaqueous capillary electrophoresis was evaluated for its potential to separate peptides in methanolic background electrolytes in comparison to aqueous-methanol (50% v/v) and water. Isomeric aspartyl dipeptides and Leu- and Met-enkephalin served as model compounds. pK(a) values were determined in the three solvent systems based on the apparent pH scale and in the case of methanol additionally based on the conventional pH scale. Changing from water to methanol led to an increase of the ionization constants describing the dissociation equilibria of the carboxyl group and the amino group, respectively. The pK(a) shift was more pronounced for the carboxylic acid function leading to a compression of the mobility-pH curve. As reported for aqueous buffers, efficient separations of the peptides were achieved in methanolic background electrolytes including the resolution of the diastereomers of the isomeric alpha- and beta-aspartyl dipeptides. In contrast to aqueous buffers, the separation of Leu- and Met-enkephalin could also be obtained in buffers in methanol at high pH.