University of North Florida
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Stuart Chalk, Ph.D.
Department of Chemistry
University of North Florida
Phone: 1-904-620-1938
Fax: 1-904-620-3535
Email: schalk@unf.edu
Website: @unf

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Ru Xiu Cai

Abbrev:
Cai, R.X.
Other Names:
Ruxiu Cai
Address:
Department of Chemistry, Wuhan University, Wuhan 430072, China
Phone:
+86-27-87684184
Fax:
+86-27-87647617

Citations 6

"Stopped-flow Spectrophotometric Determination Of Hydrogen Peroxide With Hemoglobin As Catalyst"
Talanta 2000 Volume 51, Issue 1 Pages 179-186
Ke Zhang, Luyuan Mao and Ruxiu Cai

Abstract: 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 9.2 x 10^-9 mol/l H2O2. A linear calibration graph was obtained over the H2O2 concentration range 5.0 x 10^-8-3.5 x 10^-6 mol/l, and the relative standard deviation at a H2O2 concentration of 5.0 x 10^-7 mol/l was 2.08%. Satisfied results were obtained in the determination of H2O2 in real samples by this method.
Hydrogen peroxide Rain Spectrophotometry Stopped-flow Kinetic Catalysis Interferences Optimization

"Study And Analytical Application Of Rare Earth Inhibition Of Laccase"
Talanta 1994 Volume 41, Issue 5 Pages 735-738
Cai Ruxiu, Huang Houping, Wang Guangfei, Lin Zhixin and Zeng Yun'e

Abstract: Laccase is a multi copper-containing oxidase. The effects of metal ions on the laccase-catalyzed redox reaction of 5,6-dibromo-2,3-dicyanohydroquinone to 5,6-dibromo-2,3-dicyanosemiquinone were studied. Rare-earth ions (Y, Sc, La, Lu) strongly inhibited the reaction. The degree of inhibition of La(III) on laccase activity was proportional to the concentration of La. A stopped-flow enzyme-catalyzed analytical kinetic method for determination of rare earths was proposed. The degree of inhibition of La(III) on the laccase-catalyzed reaction was linear from 0.033-0.2 ppm of La. The detection limit was 0.033 ppm and the RSD was 5.3% (n = 11). The method was used to determine rare-earth elements in water.
Metals, rare earth Environmental Biochemical analysis Stopped-flow Enzyme Kinetic Catalysis

"Determination Of Chromium(VI) By Flow Injection Spectrophotometry Coupled With Online Microcolumn Preconcentration"
Lab. Rob. Autom. 1999 Volume 11, Issue 3 Pages 141-145
Wanhong Ma, Ruxiu Cai, Danhua Chen

Abstract: A rapid and sensitive method is described for flow injection spectrophotometric determination of trace chromium (VI) in natural water. Preconcentration and elution of the trace analyte are achieved through quantitative and rapid adsorption on the surface of nanometer-size TiO2 (anatase) powders and followed by the quantitative and reproducible elution of Cr(VI) using 2.0 M HCl as an eluent. The eluted Cr(VI) reacts with 1,5-diphenylcarbazide (DPCB) in the reaction coil to form a color complex, which is then detected by a spectrophotometer at the wavelength of 540 nm. The pre-concentration factor is 55 for the sample volume of 25 mt, and the detection limit is 0.8 ng/mL Cr(VI). Under the optimized conditions, the analysis of Cr(VI) can be achieved at the rate of 6 samples/h for 0.001 µg/mL Cr(VI) or 20 samples/h for 0.1 µg/mL Cr(VI). The relative standard deviations are in the range of 0.37-3.35% (n = 5).

"Studies On Adsorption Properties Of Chromium(VI) On The Nanometer-size TiO2 Powder Surfaces Using Online Flow Injection Analysis"
Gaodeng Xuexiao Huaxue Xuebao 1998 Volume 19, Issue 10 Pages 1566-1569
Ma, W.H.;Cai, R.X.;Lin, Z.X.

Abstract: Various nanometer-size TiO2 samples are prepared from TiCl4 under different hydrolysis and calcining treatment conditions, such as pH, surfactants, stabilizers and temperature It has been found that powders heat-treated at the temperature below 450°C are of anatase crystal structure with average grain size of less than 20 nm. Adsorption behavior of Cr(VI) ion on as prepared powders, adsorption kinetics, pH curves, adsorption isotherms and adsorption capacity are studied by flow injection microcolumn system for pre-concentration using spectrophotometric detection method. The results demonstrated that nanometer-size TiO2 possesses a significant capacity and exchange rate for adsorption of Cr(VI) ion (~3080 µg/g and 8.6 x 10^3 s-1).
Chromium(VI) Spectrophotometry Kinetic Solid phase extraction

"Determination Of Hemoglobin Based On Its Enzymatic Activity For The Oxidation Of O-phenylenediamine With Hydrogen Peroxide"
Anal. Chim. Acta 2000 Volume 413, Issue 1-2 Pages 109-113
Ke Zhang, Ruxiu Cai, Danhua Chen and Luyuan Mao

Abstract: A new method has been developed for the determination of hemoglobin (Hb) based on its enzymatic activity for the oxidation of o-phenylenediamine with hydrogen peroxide. Stopped-flow spectrophotometry was used to study the kinetic behavior of the oxidation reaction. The absorbance of the reaction product, 2,3-diaminophenazine, at the wavelength of 425 nm was recorded every millisecond during the first 0.2 min of the reaction. The initial reaction rate obtained at 48°C was proportional to the concentration of Hb in the range of 8.5 x 10^-56.5 x 10^-11 mol/l. Excess of bovine serum albumin, Ca(II), Mg(II), Cu(II) and glucose did not interfere. The relative standard deviations were within 5% for the determination of different concentrations of Hb. The detection limit was found to be 3.2 x 10^-12 mol/l.
Hemoglobin Urine Spectrophotometry Stopped-flow Interferences Kinetic Optimization Indirect

"Selective Kinetic Method Based On Detecting The Intermediate Product In Successive Reactions"
Anal. Chim. Acta 1996 Volume 325, Issue 1-2 Pages 105-109
Xinguo Wu, Ruxiu Cai*, Zhixin Lin and Jieke Cheng

Abstract: A kinetic method for the analysis of binary mixtures was developed based on: (i) detecting an intermediate reaction product which has a peak-shaped kinetic curve; and (ii) selecting two measurement times (t1 and t2) where the interfering species produces two equal signal intensities and the analyte produces different signal intensities. The method was applied to the determination of epinephrine in the presence of norepinephrine using a flow injection stopped-flow technique and utilizing the alkaline oxidation of epinephrine by dissolved O2 to the indole intermediate. A sample stream was merged with a 1 M NaOH stream and the mixture was propelled to the detection cell which was maintained at 30°C. The flow was stopped and the fluorescence intensity at 510 nm (excitation at 410 nm) was monitored. The difference in the fluorescence intensities at t1 = 2 min and t2 = 8 min was used to calculate the epinephrine concentration. The calibration graph was linear for 0.2-8 µM, the detection limit was 0.04 µM and the RSD (n = 11) for 1 µM-epinephrine was 4.6%. The method was tested by analyzing synthetic mixtures containing epinephrine, dopamine, dopa and norepinephrine.
Catecholamine, derivatives Fluorescence Interferences Kinetic Stopped-flow