Qiaosheng Pu

Hollow, Spherical Nitrogen-Rich Porous Carbon Shells Obtained from a Porous Organic Framework for the Supercapacitor

Hollow, spherical nitrogen-rich porous carbon shells were prepared as supercapacitor electrode materials through the carbonization of structure-controlled porous organic frameworks at high temperature. The structure and electrochemical properties of the resulting carbonized materials were systematically characterized. Experimental results revealed that the nitrogen-rich hollow carbon spheres obtained at 800 °C were a kind of amorphous carbon with micropores on the shell frame and with specific surface areas as high as 525 m2 g(-1). The prepared porous carbon possessed a specific capacitance of 230 F g(-1) at a current density of 0.5 A g(-1) and could retain ∼98% of the initial capacitance after 1500 successive charge-discharge cycles. Electrochemical impedance spectroscopy indicated that the material has a small equivalent series resistance (0.62 Ω). All of these values demonstrated that the prepared porous carbon is a promising supercapacitor material. The proposed method represents a simple approach towards the preparation of unique structures of nitrogen-containing porous carbon that exhibit the advantages of having a simple preparation process, a wide availability of precursors, flexible control of the structure, and an easier adjustment of the amount of heteroatoms.

Synthesis of silica gel immobilized thiourea and its application to the on-line preconcentration and separation of silver, gold and palladium

A new silica gel based chelating sorbent with thiourea as a functional group was used for the flow injection (FI) on-line preconcentration and separation of trace levels of silver, gold and palladium. Its sorption characteristics were evaluated by FI-FAAS. The selected metal ions were adsorbed on a column packed with thiourea modified silica gel (TuSG) with a sampling flow rate of 5.0 ml min1, eluted with 5% thiourea with a flow rate of 2.5 ml min1 and determined by FAAS. Common co-existing ions did not interfere with the preconcentration and determination. The detection limits, defined as three times of the standard deviation of the blank (3σ), of Ag, Au and Pd are 1.3, 14 and 21 ng ml1, respectively, with a 1 min sample loading time. The RSD is not more than 3.0% for 0.040 µg ml1 of Ag, 0.20 µg ml1 of Au and 0.30 µg ml1 of Pd. With 40 min of the sample loading time, 1.0 ng ml1 of Ag, 5.0 ng ml1 of Au and 7.5 ng ml1 of Pd were successfully preconcentrated. The total dynamic capacity of TuSG was 24.5, 50.9 and 30.3 mg g1 for Ag, Au and Pd, respectively. The sorbent exhibited excellent stability. Its sorption properties did not change after 1000 cycles of use. The selected metals in a secondary nickel alloy, an anode slime, an electrolytic solution and three national certified ore samples were determined satisfactorily using the proposed method.

Application of a macroporous resin containing imidazoline groups to preconcentration and separation of gold, platinum and palladium prior to ICP-AES determination.

A new functional resin with a long functional side chain was synthesized by modification of aminated macroporous poly(vinyl chloride) resin with cyanoethylene and ethylenediamine. Traces of Au(III), Pt(IV) and Pd(II) in aqueous solution were quantitatively adsorbed in the acidity range of pH 4 and C(H(+)) 3 M. The rate of equilibration is high; Cu(2+), Fe(3+), Ni(2+), etc. exhibit little interference on the adsorption of the sought noble metals. The saturated adsorption capacities for Au(III), Pt(IV), Pd(II) and Ir(IV) in 2 M HCl were 4.0, 1.57, 2.26, 1.85 mmol g(-1). Adsorbed ions can be quantitatively desorbed by 4% thiourea +0.25 M H(2)SO(4). The resin has good reusability, and can be used for preconcentration and separation of Au(III), Pt(IV) and Pd(II) prior to their determination by ICP-AES with satisfactory results.

Rapid and sensitive determination of sulfonamide residues in milk and chicken muscle by microfluidic chip electrophoresis.

A new, rapid, and sensitive method was proposed for the determination of sulfonamide residues in milk and chicken muscle samples by microchip electrophoresis with laser-induced fluorescence detection. Separation of fluorescamine-labeled sulfonamides was accomplished by using a buffer containing 5 mmol/L boric acid and 1% (w/v) polyvinyl alcohol (PVA). The pH, amount of PVA, and concentration of boric acid in the running buffer were found to have great influence on the separation. By optimizing these conditions, the separation of four sulfonamides, sulfamethazine, sulfamethoxazole, sulfaquinoxaline, and sulfanilamide, was achieved within 1 min with limits of detection (S/N = 3) of 0.2-2.3 μg/L, which are well below the maximum residue limit. The proposed method also exhibited very good repeatability; the relative standard deviations for both within-day and between-day measurements were ≤3.0%. With a simplified sample pretreatment protocol, fast determination of sulfonamides in real samples was successfully performed with standard addition recoveries of 93.3-100.8 and 82.9-92.3%, respectively.

Microwave-accelerated derivatization for capillary electrophoresis with laser-induced fluorescence detection: A case study for determination of histidine, 1- and 3-methylhistidine in human urine

The feasibility of microwave-accelerated derivatization for capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection was evaluated. The derivatization reaction was performed in a domestic microwave oven. Histidine (His), 1-methylhistidine (1-MH) and 3-methylhistidine (3-MH) were selected as test analytes and fluorescein isothiocyanate (FITC) was chosen as a fluorescent derivatizing reagent. Parameters that may affect the derivatization reaction and/or subsequent CE separation were systematically investigated. Under optimized conditions, the microwave-accelerated derivatization reaction was successfully completed within 150 s, compared to 4-24 h in a conventional water-bath derivatization process. This will remarkably reduce the overall analysis time and increase sample throughput of CE-LIF. The detection limits of this method were found to be 0.023 ng/mL for His, 0.023 ng/mL for 1-MH, and 0.034 ng/mL for 3-MH, respectively, comparable to those obtained using traditional derivatization protocols. The proposed method was characterized in terms of precision, linearity, accuracy and successfully applied for rapid and sensitive determination of these analytes in human urine.

Fast and interference-free determination of glyphosate and glufosinate residues through electrophoresis in disposable microfluidic chips

With an increasing concern on food safety, fast screening of residues of widespread herbicides becomes necessary. Herein we report a microchip electrophoresis system with laser induced fluorescence (LIF) detection for rapid and sensitive analysis of glyphosate (GLYP) and glufosinate (GLUF) residues. Disposable cyclic olefin copolymer microchips and a low-cost LIF detector were employed to minimize the cost of the analysis. Systematic optimization of experimental conditions was performed to achieve highly efficient analysis. Under the selected condition, GLYP and GLUF were efficiently resolved from sample matrices with a buffer containing 10 mmol/L borax and 2.0% (m/v) hydroxypropyl cellulose at pH 9.0. The number of theoretical plates of 1.0×10(6) m(-1) was attained for both analytes. Derivatization at lower concentrations (<10 μg/L) was also examined, successful detection of 0.34 μg/L GLYP and 0.18 μg/L GLUF was confirmed. The system was applied for the determination of both analytes in real samples without any preconcentration involved. Recoveries of GLYP and GLUF spiked in these samples were 84.0-101.0% and 90.0-103.0%, respectively.

Chip-capillary hybrid device for automated transfer of sample preseparated by capillary isoelectric focusing to parallel capillary gel electrophoresis for two-dimensional protein separation.

In this article, we introduce a chip-capillary hybrid device to integrate capillary isoelectric focusing (CIEF) with parallel capillary sodium dodecyl sulfate- polyacrylamide gel electrophoresis (SDS-PAGE) or capillary gel electrophoresis (CGE) toward automating two-dimensional (2D) protein separations. The hybrid device consists of three chips that are butted together. The middle chip can be moved between two positions to reroute the fluidic paths, which enables the performance of CIEF and injection of proteins partially resolved by CIEF to CGE capillaries for parallel CGE separations in a continuous and automated fashion. Capillaries are attached to the other two chips to facilitate CIEF and CGE separations and to extend the effective lengths of CGE columns. Specifically, we illustrate the working principle of the hybrid device, develop protocols for producing and preparing the hybrid device, and demonstrate the feasibility of using this hybrid device for automated injection of CIEF-separated sample to parallel CGE for 2D protein separations. Potentials and problems associated with the hybrid device are also discussed.

Facile one-step photochemical synthesis of water soluble CdTe(S) nanocrystals with high quantum yields

This paper describes a successful synthesis of water soluble CdTe(S) nanocrystals (NCs) with high quantum yields (QYs) via a mild photochemical route in one step with thioglycolic acid as the stabilizer and sulfur source. The precursor solution of mixed cadmium chloride, freshly prepared sodium hydrogen telluride and thioglycolic acid was subjected directly to UV irradiation using a 500 W high-pressure mercury lamp under the protection of N2. NCs with a small particle size (2.2 nm) and a high photoluminescence quantum yield (up to 80% at room temperature) were formed within 25 min. The NCs were characterized by UV-vis absorption and fluorescence spectroscopy, transmission electron microscopy, powder X-ray diffraction and energy-dispersive X-ray spectroscopy to evaluate their structure, size and composition. The photochemically prepared NCs were compared with CdTe NCs prepared by conventional hydrothermal synthesis and CdTe/CdS core/shell NCs obtained by post-preparative photochemical passivation. The effects of UV irradiation intensity, illumination time, temperature and concentration of Te2− on the optical properties of NCs were studied in detail.

High-Pressure Open-Channel On-Chip Electroosmotic Pump for Nanoflow High Performance Liquid Chromatography

Here, we construct an open-channel on-chip electroosmotic pump capable of generating pressures up to ∼170 bar and flow rates up to ∼500 nL/min, adequate for high performance liquid chromatographic (HPLC) separations. A great feature of this pump is that a number of its basic pump units can be connected in series to enhance its pumping power; the output pressure is directly proportional to the number of pump units connected. This additive nature is excellent and useful, and no other pumps can work in this fashion. We demonstrate the feasibility of using this pump to perform nanoflow HPLC separations; tryptic digests of bovine serum albumin (BSA), transferrin factor (TF), and human immunoglobulins (IgG) are utilized as exemplary samples. We also compare the performance of our electroosmotic (EO)-driven HPLC with Agilent 1200 HPLC; comparable efficiencies, resolutions, and peak capacities are obtained. Since the pump is based on electroosmosis, it has no moving parts. The common material and process also allow this pump to be integrated with other microfabricated functional components. Development of this high-pressure on-chip pump will have a profound impact on the advancement of lab-on-a-chip devices.

FAAS Determination of Platinum Using an On-Line Separation and Preconcentration System with a Polymelamine Dendrimer Immobilized Silica Gel

Abstract A G4.0 polymelamine dendrimer based on silica gel (PMDSG) was fabricated via a divergent approach via repetitive reaction of 2,4,6-trichloro-1,3,5-triazine and 1,6-hexylenediamine from a γ-aminopropyl silica gel (APSG) core for the first time. It was then used as the microcolumn packings for the flow injection (FI) preconcentration and separation of trace or ultra trace Pt(IV) for the flame atomic absorption spectrometry determination. A limit of detection (LOD) of 0.065 µg mL−1 was achieved when a 0.500 µg mL−1 Pt(IV) was preconcentrated at pH 3.0 with a sampling flow rate of 5.0 mL min−1 for 60 s and the relative standard deviation (RSD) was no more than 5.0%. The proposed method was successfully used for the determination of Pt in two metallurgical samples.