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Qishu Qu

Publications and source records attributed to Qishu Qu.

7 recordsLinked to original sources
PubMed2006

Differential pulse voltammetric determination of nimesulide in pharmaceutical formulation and human serum at glassy carbon electrode modified by cysteic acid/CNTs base on electrochemical oxidation of L-cysteine.

Carbon nanotubes (CNTs) and cysteic acid based on electrochemical oxidation of L-cysteine (CySH) to form a novel composite thin film material at a glassy carbon electrode (GCE) for electroanalytical determination of nimesulide. The determination of nimesulide at the composite modified electrode with strong accumulation of nimesulide was studied by differential pulse voltammetry (DPV). The peak current obtained at +1.251 V (versus SCE) from DPV was linearly dependent on the nimesulide concentration in the range of 1.0 x 10(-7) -1.0 x 10(-5) M in 0.05 M H(2)SO(4) solution with a correlation coefficient of 0.997. The detection limit (S/N = 3) was found to be 5.0 x 10(-8) M. The low-cost modified electrode showed good sensitivity, selectivity, stability and had been applied to the determination of nimesulide in pharmaceutical formulation and human serum samples with satisfactory results.

Carbon↗
PubMed2006

Preparation and evaluation of C18-bonded 1-microm silica particles for pressurized capillary electrochromatography.

Nonporous silica spheres (1 microm) were synthesized and bonded with octadecylsilane functionality. These stationary phase particles were packed electrokinetically into fused-silica capillaries with 100 microm id for a length of 20 cm, which was evaluated by using pressurized CEC (pCEC). The efficiency of the C18 RP column was characterized through the theoretical plates of thiourea, benzyl alcohol, toluene, styrene, and naphthalene. The effects of experimental parameters such as the applied voltage, sample size, pump flow rate, pH value and the concentration of the buffer solution, and the content of methanol in the mobile phase, on-column efficiency were evaluated. Column efficiency as high as 200 000 theoretical plates per meter for naphthalene was obtained with the optimal condition of 70% v/v methanol and 30% v/v of 10 mmol/L phosphate buffer (pH 7.8) at an applied voltage of 10 kV and a supplementary pressure of 500 psi.

Benzyl Alcohol↗
PubMed2006

Etched bare fused-silica capillaries for online preconcentration of amino acids in CE.

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.

Amino Acids↗
PubMed2006

Preparation of particle-fixed silica monoliths used in capillary electrochromatography.

Fused-silica capillarieswere packed with porous 1 microm bare silica microspheres and immobilized by potassium silicate-formamide in order to obtain columns with silica-based monolithic packing. After curing, the particle-fixed monolithic columns were octadecylated insitu with dimethyloctadecylchlorosilane. The columns were mechanically strong and permeable. No noticeable loss in efficiency was found after using a column continuously for 1 month. The performances of the particle-fixed silica monolithic columns were evaluated for CEC under RP conditions. High separation efficiency (about125 200 plates/m) was obtained by using these new types of columns.

Journal Article↗
PubMed2004

Reduced-bore monolithic silica column modified with C8-TEOS for reversed-phase electrochromatography.

Monolithic silica columns of 2.7 mm ID were prepared and derivatized with C8-TEOS and TEOS by on-column sol-gel reaction. These C8 large diameter monolithic silica columns gave 21 000 theoretical plates for aromatic hydrocarbons in 60% acetonitrile and 40% Tris-HCI buffer. The surface areas as well as the separation reproducibility were improved on coating by the sol-gel approach. Joule heating was greatly reduced by using monolithic columns to which fine quartz sand had been added during column preparation. Since this is a preliminary investigation on a monolithic column with such a large inner diameter, the separation efficiency was not so high as that presently achieved in normal capillary electrochromatography (CEC). However, use of the columns improved sample loadability and concentration detectability of electrochromatography, and semi-preparative separations could be performed.

Journal Article↗
PubMed2004

Packing capilllary electrochromatography columns using vacuum--a preliminary study.

This paper introducesa novel method for packing Capillary Electrochromatography Columns (CEC). Using vacuum packing methodology, silica particles as small as 1 microm were successfully packed into the capillary columns with 75 microm inner diameter. The columns are verystable and show no noticeable loss in efficiency after 200 sample injections. The performance of these vacuum packed capillary columns was evaluated with a mixture of aromatic and non-aromatic compounds. A 24 cm long capillary column can produce peak efficiencies of around 45,000 plates for benzene.

Journal Article↗