Yonglei Chen

Application of 1-alkyl-3-methylimidazolium-based ionic liquids as background electrolyte in capillary zone electrophoresis for the simultaneous determination of five anthraquinones in Rhubarb

A capillary zone electrophoresis method using only 1-alkyl-3-methylimidazolium-based ionic liquids as background electrolyte for the simultaneous determination of five anthraquinone derivatives including aloe-emodin, emodin, chrysophanol, physcion and rhein in Rhubarb species was described. Ion association constants, K(ass), between anthraquinone anions and imidazolium cations were determined by analyzing the electrophoretic mobility change of anthraquinone anions using a non-linear least-squares method and factors contributing to ion associability were systematically clarified. For method optimization, several parameters such as ionic liquids concentration, background electrolyte pH and applied voltage, on the separation were evaluated and the optimum conditions were obtained as follows: 90mM 1-butyl-3-methylimidazolium tetrafluoroborate (pH 11.0) with an applied voltage of 20kV. Under these conditions, the method has been successfully applied to the determination of anthraquinones in extracts of two kinds of Rhubarb plants (R. palmatum and R. hotaoense) within 12min. The method proposed herein was shown to be much simpler than the previously reported methods.

Review of recent developments of on-line sample stacking techniques and their application in capillary electrophoresis

AbstractCapillary electrophoresis (CE) has become one of the most useful tools in separation science because of its high separation efficiency, low cost, versatility, ease of sample preparation and automation. However, some limitations of CE, such as poor concentration sensitivity due to its lower sample loading and shorter optical path length, limits its further applications in separation science. In order to solve this problem, various on-line sample preconcentration techniques such as transient isotachophoresis preconcentration, field-enhanced sample stacking, micelle to solvent stacking, micelle collapse, dynamic pH junction, sweeping, solid phase extraction, single drop microextraction and liquid phase microextraction have been combined with CE. Recent developments, applications and some variants together with different combinations of these techniques integrating in CE are reviewed here and our discussions will be confined to the past three years (2008–2011).n

Methyl-triclosan binding to human serum albumin: Multi-spectroscopic study and visualized molecular simulation

Methyl-triclosan (MTCS), a transformation product and metabolite of triclosan, has been widely spread in environment through the daily use of triclosan which is a commonly used anti-bacterial and anti-fungal substance in consumer products. Once entering human body, MTCS could affect the conformation of human serum albumin (HSA) by forming MTCS-HSA complex and alter function of protein and endocrine in human body. To evaluate the potential toxicity of MTCS, the binding mechanism of HSA with MTCS was investigated by UV-vis absorption, circular dichroism and Fourier transform infrared spectroscopy. Binding constants, thermodynamic parameters, the binding forces and the specific binding site were studied in detail. Binding constant at room tempreture (T = 298K) is 6.32 × 10(3)L mol(-1); ΔH(0), ΔS(0) and ΔG(0) were 22.48 kJ mol(-1), 148.16 J mol(-1)K(-1) and -21.68 kJ mol(-1), respectively. The results showed that the interactions between MTCS and HSA are mainly hydrophobic forces. The effects of MTCS on HSA conformation were also discussed. The binding distance (r = 1.2 nm) for MTCS-HSA system was calculated by the efficiency of fluorescence resonance energy transfer. The visualized binding details were also exhibited by molecular modeling method and the results could agree well with that from the experimental study.

Simultaneous determination of iridoid glycosides and flavanoids in Lamionphlomis rotate and its herbal preparation by a simple and rapid capillary zone electrophoresis method

Iridoid glycosides and flavanoids are two main effective components of Lamiophlomis rotata (Benth.) kudo. However, there is no method for simultaneous analysis of iridoid glycosides and flavanoids in L. rotata and its pharmaceutical preparations. A simple and rapid capillary zone electrophoresis (CZE) method was developed and validated for simultaneous determination of two iridoid glycosides (8-O-acetylshanzhiside methylester and 8-deoxyshanzhiside) and three flavanoids (apigenin, quercetin and luteolin) in L. rotata. Operational variables, such as the voltage, buffer concentration and pH were optimized, the final optimum separation condition was 10 mM sodium tetraborate-20 mM NaH(2) PO(4) (pH 8.5)-15% (v/v) methanol, 238 nm UV detection, 18 kV applied voltage. The linearity and the recovery of the proposed method were very satisfactory (correlation coefficients were 0.9994-0.9998 and the recoveries were 94.5-108.8% for the analytes) and the method allowed analytes in real samples to be determined within 9 min. The proposed CZE method can be used for quality control of iridoid glycosides and flavanoids in L. rotata and its herbal preparation.

One-pot, large-scale synthesis silica-encapsulated NIR alloy quantum dots CdSeTe within short time

Silica-based near-infrared fluorescent materials in biological application have attracted much attention. But the current methods for preparing silica-encapsulated near-infrared radiation (NIR) quantum dots (QDs) are commonly time-consuming and can only obtain a few products in one batch. Herein, we present a fast and facile one-pot aqueous-phase route to prepare NIR-emitting silica-encapsulated CdSeTe QDs at large scale. The influences of various experimental conditions on the luminescent properties of the obtained silica hybrids QDs have been systematically investigated, such as capping agent, reaction time, pH value and so on. The final product has been characterized by X-ray diffraction, transmission electron microscope, photoluminescent spectra and energy dispersive x-ray spectroscopy (EDX). The silica-coated NIR-emitting QDs can be obtained within 10xa0h under the optimized conditions. The yield is 3.70xa0g in one batch. The final product is spherical with an average particle size around 15xa0nm.

OPTIMIZATION OF THE MICELLAR ELECTROKINETIC CAPILLARY CHROMATOGRAPHIC DETERMINATION OF DAURICINE AND DAURISOLINE IN RHIZOMA MENISPERMI AND ITS HERBAL MEDICINE USING EXPERIMENTAL DESIGN AND RADIAL BASIS FUNCTION NEURAL NETWORK

Orthogonal design has been applied to the optimization of separation and determination of dauricine and daurisoline in Rhizoma Menispermi and its herbal medicine by micellar electrokinetic capillary chromatography. Operational variables, such as the voltage, micelle concentration, buffer concentration and pH were optimized. Their different effects on peak resolution were studied by the experimental design method. Optimized separation conditions were obtained and successfully applied to the separation and determination of dauricine and daurisoline in real samples. The proposed method allows alkaloids in real samples to be determined within 15 min using a buffer system composed of 25 mM HAc, 25 mM NaAc and 2% polyoxyethylene sorbitan monolaurate (Tween-20) (pH 4.5). In addition, a radial basis function neural network with a “4-18-1” structure was developed based on the experimental results of orthogonal design and uniform design, and applied to the prediction of peak resolution of dauricine and daurisoline under the optimum separation conditions given by orthogonal design. The predicted results were in good agreement with the experimental values, indicating that radial basis function neural network may be a potential method for the selection of separation conditions in capillary electrophoresis.