Wei Wanzhi

Theory and application of analytical spectroelectrochemistry with long path length spectroelectrochemical cells: Part I. Integral equation connecting the absorbance with the concentration distribution and its use in digital simulation for long path length thin layer spectroelectrochemical cells

Abstract An integral equation connecting the absorbance with the concentration distribution for analytical spectroelectrochemistry in long path length cells was derived. On the basis of the numerical integration form of the equation a finite difference model for digital simulation of the long path length thin layer spectroelectrochemical cell with a single potential step was set up. The concentration distribution at different moments determined with the technique was confirmed by theoretical results and the variation with time of the simulated absorbance curve was in agreement with that obtained by experiment, and hence the treatment can be applied for the estimation of parameter and the study of kinetics and mechanisms of electrochemical systems.

Theory and application of analytical spectroelectrochemistry with long path length spectroelectrochemical cells: Part II: non-linear regression analysis of analytical spectroelectrochemical data for estimation of electrochemical parameters

Abstract The non-linear parameter model underlying single potential step spectroelectrochemical determination of heterogeneous electron transfer rate constants with a long path length cell is presented. Based on the theoretical A — t response model, the computerized non-linear regression can be used to analyse individual spectroelectrochemical response curves to estimate parameters and study mechanisms for many true systems. The regression results of the Fe(CN)63−/Fe(CN)64− quasi-reversible response curves for estimation of the forward heterogeneous electron transfer rate constant are of high precision owing to the high optical sensitivity of the procedure. The method is rapid and accurate for parameter estimation and can be readily adapted to complex electrochemical mechanisms.

New amperometric glucose biosensor by entrapping glucose oxidase into chitosan/nanoporous ZrO2/multiwalled carbon nanotubes nanocomposite film

A new nanocomposite material for construction of glucose biosensor was prepared. The biosensor was formed by entrapping glucose oxidase(Gox) into chitosan/nanoporous ZrO2/multiwalled carbon nanotubes nanocomposite film. In this biosensing thin film, the multiwalled carbon nanotubes can effectively catalyze hydrogen peroxide and nanoporous ZrO2 can enhance the stability of the immobilized enzyme. The resulting biosensor provides a very effective matrix for the immobilization of glucose oxidase and exhibits a wide linear response range from 8 μmol/L to 3 mmol/L with a correlation coefficient of 0.994 for the detection of glucose. And the response time and detection limit of the biosensor are determined to be 6 s and 3.5 μmol/L, respectively. Another attractive characteristic is that the biosensor is inexpensive, stable and reliable.

Comparison of simultaneous distillation extraction and solid-phase micro-extraction for determination of volatile constituents in tobacco flavor

The volatile and semi-volatile components in tobacco flavor additives were extracted by both simultaneous distillation extraction and solid-phase micro-extraction. Extraction conditions for solid-phase micro-extraction were optimized with information theory. Then, detection were accomplished by gas chromatography-mass spectrometry. Characteristic of each method was compared. Qualitative analysis and quantitative analysis of 6# tobacco flavor sample were accomplished through both simultaneous distillation extraction and solid-phase micro-extraction. The experimental results show that solid-phase micro-extraction method is the first choice for qualitative analysis and simultaneous distillation extraction is another good selection for quantitative analysis. By means of simultaneous distillation extraction, 20 components are identified, accounting for 92.77% of the total peak areas. Through solidphase micro-extraction, there are 17 components identified accounting for 91.49% of the total peak areas. The main aromatic components in 6# tobacco flavor sample are propanoic acid, 2-hydroxy-, ethyl ester, menthol and menthyl acetate. The presented method has been successfully used for quality control of tobacco flavor.

A Selective Pharmaceutical Analysis Technique with Sensitive Piezoelectric Crystal Quartz Sensors

Abstract The frequency shift of a piezoelectric crystal sensor showed a linear dependence on the concentration for drugs which can be hydrolyzed in base aqueous solutions, at a given reacting time after the addition of the base, when the base concentration is basically constant during the entire measurement period. The sensitivity of the analysis method was improved, if crystal responses at different reacting times were recorded and utilized to estimate component concentration, when used for determining atropine sulfate in a pharmaceutical compound. The analytical results indicated that the selective and sensitive analytical procedure could be easily applied in true low concentration pharmaceutical analysis.

Calibration method for determination of acids and bases with piezoelectric quartz crystal sensors

Based on the linear relation between the frequency response of the piezoelectric quartz crystal sensor and the conductivity of the solution to be measured, calibration models for quantitative analysis of acid and base systems are derived and are verified both theoretically and experimentally. Then quantitative determinations of aspirin and penicilline were done with the calibration technique. The quantitative analysis results of the two true pharmaceutical systems indicate that the models, combining linear regression, can give precise and accurate concentration estimates, which can reduce the influence of the presence of interferences.

Differential linear sweep and differential cyclic voltabsorptometry in a long-path-length spectroelectrochemical cell: Eqr, Eir and ErCi′

Abstract The theory of differential linear sweep voltabsorptometry (DLSVA) and differential cyclic voltabsorptometry (DCVA) in long-path-length spectroelectrochemistry is presented for irreversible (Eir), quasi-reversible (Eqr) and ErCi′ mechanisms under conditions of semi-infinite diffusion. It is concluded that this method may be suitable for estimating electrochemical parameters because it is more sensitive than the approach using an optically transparent electrode. All the theoretical results re experimentally verified. The standard heterogeneous rate constant k s and the transfer coefficient α of two electrochemical quasi-reversible systems (methylene blue in 1.0 M HCl and indigo carmine in 0.1 M HCl) were estimated using the simplex method and good fits between theory and experiment were obtained. A system comprising K 4 Fe(CN) 6 + ascorbic acid in 0.5 M HNO 3 + 0.5 M glycine buffer was utilized to test the theory for the ErCi′ mechanism. The rate constant of the pseudo-first-order catalytic reaction was also estimated by simplex fitting. The estimated results are in agreement with experimental values.

A series piezoelectric quartz crystal response kinetics for T. ferrooxidans growth in the presence of Cu(II)

The kinetics on the growth of T. ferroxidans in the presence of Cu(II) was studied using of series piezoelectric quartz crystal (SPQC). Arsenic ion inhibits the growth of T. ferrooxidans, which is consistent with the previous results by other measuring methods. This further demonstrates that the SPQC can monitor the chemical activity of T. ferrooxidans growth. Cupric ion accelerates the growth of T. ferrooxidans. The mechanism was discussed, i. e., copper promotes the protein enzyme of T. ferrooxidans, rusticyanin, to form over the range of cupric ion concentration studied. The reaction order of cupric ion in accelerating the bacterial growth is 0.067. The growth of T. ferrooxidans is dependent on temperature, the apparent reaction activation energy decreases from 25.56 kJ/mol to 18.32 kJ/mol because of the addition of 10 mg/L Cu(II) to the bacterial growth solution of pH 2.0 at initial inoculum of 10%.

Application of ridge trace analysis in direct spectrophotometric calibration

The use of ridge trace analysis for multivariate calibration problems is described. Application is made to the simultaneous quantitative determination of components for several pharmaceutical systems with unknown sample UV spectra by the direct calibration technique. The results indicate that with the help of ridge trace analysis and ridge regression, the parameter k can be selected to obtain estimation of the colinearity of a system based on the stability of relative concentration as a function of k. Much information about the system to be analyzed can be obtained, such as whether there is colinearity among the variables, which measurement wavelength range is suitable for performing quantitative analysis, which components cannot be measured and which components can only be measured as a sum, and whether the quantitative model is correct.