Ruxiu Cai

Stopped-flow spectrophotometric determination of hydrogen peroxide with hemoglobin as catalyst

A rapid and sensitive method was proposed for the determination of hydrogen peroxide based on the catalytic effect of hemoglobin using o-phenylenediamine as the substrate. Stopped-flow spectrophotometric method was used to study the kinetic behavior of the oxidation reaction. The catalytic effectiveness of hemoglobin was compared with other four kinds of catalysts. The initial rate of the formation of the reaction product 2,3-diaminophenazine at the wavelength of 425 nm was monitored, permitting a detection limit of 9.2x10(-9) mol/l H(2)O(2). A linear calibration graph was obtained over the H(2)O(2) concentration range 5.0x10(-8)-3.5x10(-6) mol/l, and the relative standard deviation at a H(2)O(2) concentration of 5.0x10(-7) mol/l was 2.08%. Satisfied results were obtained in the determination of H(2)O(2) in real samples by this method.

Highly sensitive spectrofluorimetric determination of hydrogen peroxide with β-cyclodextrin–hemin as catalyst

β-Cyclodextrin (CD)–hemin was studied as a replacement for horseradish peroxidase (HRP) in the spectrofluorimetric determination of H2O2. The optimum concentrations of substrate and β-CD–hemin were studied. pH 10.4 was found to be the optimum value for the experiment. The influence of different buffers on the peroxidase activity of β-CD–hemin was tested and it was found that the peroxidase activity of β-CD-hemin was enhanced by NH3. The oxidation product 2,2′-dihydroxy-4,4′-dimethylbiphenyl was monitored fluorimetrically, with a detection limit of 3.4 × 10–9 mol l–1 of H2O2. A linear calibration graph was obtained over the H2O2 concentration range 3 × 10–8–8 × 10–6 mol l–1, with a correlation coefficient of 0.9993. The relative standard deviation at an H2O2 concentration of 2 × 10–6 mol l–1 was 1.8%.

Resonance light scattering spectroscopy study of interaction between gold colloid and thiamazole and its analytical application

In this paper, we used resonance light scattering (RLS) spectroscopy to study the interaction between thiol-containing pharmaceutical-thiamazole and gold colloid. At pH 5.2, the resonance light scattering spectrum of gold nanoparticles has a maximum peak at 555 nm and the RLS intensity is enhanced by trace amount of thiamazole due to the interaction between thiamazole and gold colloid. The binding of colloidal gold to thiamazole results in ligand-induced aggregation of colloidal gold, which was characterized by RLS spectrum, ultraviolet-visible (UV-Vis) spectrum, and transmission electron microscopy (TEM). Based upon the study, we proposed a highly sensitive, gold colloid-based assay using RLS spectrum to detect pharmaceuticals for the first time. The mechanism of binding interaction between Au colloid and thiamazole was also discussed.

Controlled synthesis of NaYF4: Yb, Er nanocrystals with upconversion fluorescence via a facile hydrothermal procedure in aqueous solution

Controlled synthesis of NaYF4: Yb, Er nanocrystals with upconversion fluorescence is achieved in aqueous solution by adjusting solvent composition (ethanol-to-water volume ratio) and F−/Ln3+molar ratio via a facile hydrothermal method.

A simple new way to prepare anatase TiO2 hydrosol with high photocatalytic activity

Anatase TiO2 hydrosol was prepared by hydrolyzation of tetrabutyl titanate followed by acidic peptization of the precipitate under 70 °C. The method was highly simplified and the growth of TiO2 nanocrystallites that bothered traditional preparations was avoided. The photocatalytic activity of the hydrosol was confirmed through the photocatalytic degradation of methyl blue dye under visible light irradiation.

Flow-injection stopped-flow spectrofluorimetric kinetic determination of total ascorbic acid based on an enzyme-linked coupled reaction

Abstract A flow-injection enzymatic kinetic spectrofluorimetric procedure for determining total ascorbic acid in solution by combining the merging zones principle with the stopped-flow technique is described. It is based on the oxidation of ascorbic acid catalysed by laccase to dehydroascorbic acid, which then reacts with o -phenylenediamine to form a fluorescent quinoxaline. Total ascorbic acid is determined in the range of 0.025–1.0 μg ml −1 at 30 determinations per h. The procedure is applied to the determination of total ascorbic acid in wine, beer, urine and pharmaceutical preparations.

A new method for determination of uric acid by the lactic acid-acetone-BrO3--Mn2+-H2SO4 oscillating reaction using the analyte pulse perturbation technique

A new analytical method for the determination of uric acid (UA) by the perturbation of UA on the Belousov-Zhabotinsky oscillating reaction is proposed. The method is based on the linear relationship between the changes in the oscillating period and the concentration of UA. The calibration curve is linear over the range of 2.0 x 10(-5) to 5.0 x 10(-4)M, with a detecting limit of 3.28 x 10(-6)M. The method features good precision (R.S.D.: 3.59%) and excellent throughput (10samplesh(-1)). The possible mechanism of the perturbation of UA on the oscillating reaction is discussed.

Study of the fluorescence characteristics of norfloxacin in reversed micelles and application in analysis

The fluorescence characteristics of norfloxacin (NFLX) were studied in reversed micelles which formed with sodium bis(2-ethylhexyl) sulfosuccinate (AOT)-water-octane. The influences of the environmental factors, such as the water content, AOT concentration and pH, on the fluorescence of NFLX were investigated. A novel spectrofluorimetric method for the direct determination of NFLX is proposed based on the enhancement effect of reversed micelles on the native fluorescence of NFLX, which showed a much lower detection limit (0.0032 microgram mL-1) and a wider linear range (0.015-3.8 micrograms mL-1) compared with aqueous solution.

Micelle Enhanced Spectrofluorimetric Determination of Norfloxacin Using Terbium as Fluorescent Probe

Abstract Terbium(III) forms highly fluorescent complex with norfloxacin. The presence of surfactant can enhance greatly fluorescence intensity. In this paper, the fluorescence characteristics of complex in presence of surfactant has been investigated. It was found that norfloxacin could form stable complex with terbium in the pH 6.5–8.5 media. The fluorescence intensity of complex in SLS media is three folds more than complex itself. A new micelle enhancement spectrofluorimetry for the determination of norfloxacin has been developed. The detection limit of proposed method is 0.017 μg/ml. It has been satisfactory for the determination of trace norfloxacin in serum with 95.2%∼101.2% recoveries.

Kinetic analysis of consecutive reactions using a non-linear least-squares error-compensation algorithm

An error-compensation algorithm based on a kinetic model of detecting intermediates in consecutive first-order reactions using the non-linear least-squares method was developed. A simulation study revealed that the algorithm performed well in compensating for the system error and eliminating random noise. It could offset the deficiency of low precision in kinetic analysis. The algorithm was applied to the determination of epinephrine, and the results were found to be reliable when the rate constants changed according to the variation of the experimental variables.