摘要:

AbstractA conducting, chemically synthesized, Cu(II)‐containing poly(3‐methylthiophene) powder was pressed into a pellet and used as the working electrode of a three‐electrode system in a thin‐layer amperometric cell unit to detect ionic analytes in an aqueous stream by flow‐injection analysis. The electrode response was linearly correlated with the applied voltage, which was varied between 0.2 and 3.0 V (vs. Ag/AgCI). It was shown that the electrode possesses favorable sensitivity and stability in comparison with other metallic electrodes such as stainless steel and Pt. During a period of more than a year, it showed no deterioration in its pe

ISSN:1040-0397    

DOI:10.1002/elan.1140020103

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractAn analysis scheme is presented that separates the individual effects of complexing agents and surfactants on the deposition and stripping steps in trace metal determination by differential pulse anodic stripping voltammetry (DPASV) at a hanging mercury drop electrode. The method involves DPASV measurements of total and electroactive (ASV‐labile) metal in pH 7.0 phosphate buffer before and after medium exchange, with and without acidification of the sample solution. Copper, lead, and cadmium were determined in the presence of Triton X‐100, a nonionic detergent, and the complexing agents fulvic and humic acids. Both the complexing agents and the surfactant affected deposition more than stripping, although Triton X‐100 had a significant effect on the stripping process. Triton X‐100 also acted as a complexing agent towards copper. Application of the analysis scheme to pristine and polluted freshwater samples showed that the decrease in the electroactivity of copper and lead was principally caused by the effect of surfactants on deposition. This study underlined the limitations of high‐frequency ASV techniques (e.g., DPASV) at a hanging mercury drop electrode for the determination of the toxic fraction of metals in water samples and raised questions about the usefulness of ASV copper complexing capacity titrations for water toxicity inves

ISSN:1040-0397    

DOI:10.1002/elan.1140020104

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractThe construction and utilization of a column‐shaped in situ thin‐layer ESR spectroelectrochemical cell for both ambient and low temperature operation is reported. The working electrode is a columnshaped expanded platinum sheet of 9.4 × 4.0 mm that is placed in a 0.25 mm thick column‐shaped, thin‐layer chamber. The solution volume in the thin‐layer chamber is 12 μL, and the total solution volume in the cell ranges between 1 and 3 mL. The application of this cell is demonstrated by time‐resolved ESR spectra for electrooxidized porphyrins in methylene chloride solutions containing 0.3 M tetrabutylammonium perchlorate. The electrochemical behavior of this cell is also demonstrated by the oxidation of ferrocene under the same solution conditions at temperatures between 23 and −75°C. Well‐defined ESR spectra are obtained in as short as 5–10 seconds witho

ISSN:1040-0397    

DOI:10.1002/elan.1140020105

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractA large number of anodic oxygen‐transfer reactions were studied at Au electrodes in both acidic and alkaline media. Results of competitive adsorption studies are interpreted and support the conclusion that adsorption is a prerequisite to subsequent oxygen‐ and electron‐transfer steps. Many of these oxidation reactions gave the voltammetric appearance of reversible waves, even though the observed half‐wave potential values were shifted hundreds of millivolts positive of the thermodynamic potentials. A catalytic mechanism is proposed in which adsorbed hydroxyl radicals (AuOH) participate in the oxygen‐transfer step. The absence of pH effects on half‐wave potentials for several inorganic compounds suggests that the electron transfer precedes the deprotonation step for thes

ISSN:1040-0397    

DOI:10.1002/elan.1140020106

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractThe voltammetric reduction behavior of ozone in an acidic solution was examined at gold, platinum, glassy carbon, and graphite reinforcement carbon (GRC) electrodes. The GRC electrode, the lead of a mechanical pencil, exhibited a well‐defined ozone reduction wave at 0.8–0.9 V versus a saturated calomel electrode (SCE) on a flat base current, whereas gold and glassy carbon electrodes were insensitive or nonselective to ozone. The platinum electrode showed no base current and, hence, made background correction difficult. The response was not degraded by long exposures of the GRC electrode to the ozonized solution. The reduction of ozone at the GRC electrode was controlled by a sluggish charge‐transfer step and diffusion. Differential pulse voltammetric peak current showed a linear variation with ozone concentration up to the detection limit of 6 × 10−7mol/dm3ozone in acidic solutions. Residual ozone in tap water disinfected by chlorine was determined by the present method; a linear calibration curve was also

ISSN:1040-0397    

DOI:10.1002/elan.1140020107

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractCyclic voltammetry was used for the determination of the association constants of Pb2+and Cd2+with deoxyribonucleic acid. The adsorption of the biological polyelectrolyte at the mercury electrode surface was controlled by the alternating current voltammetric method, which permits corrective factors to be introduced in the evaluation of cyclic voltammetric responses. The results are based on the analysis of the labile complexation of the slow‐diffusing DNA by studying the current intensity peak as well as the peak potential shift of Pb2+and Cd2+. The association constants (β) obtained from the two treatments are in satisfactory agreement. The dependence of the conditional association constant (β1) for the Cd‐DNA system on the monovalent ion (Na+) concentration is also rep

ISSN:1040-0397    

DOI:10.1002/elan.1140020108

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractThe electrochemical behavior of thiocinnamamide in aqueous solutions with 5% (v/v) ethanol was studied by dc and ac polarography and cyclic voltammetry. In acidic media, the reduction of thiocinna mamide occurs in the adsorbed state, giving a single dc wave. In alkaline solutions, the reduction starts at the negative limit of the adsorption potential range and produces two poorly separated dc waves. The first corresponds to the reduction of the adsorbed molecules with a strong dependence of the adsorption coefficient on the electrode potential. The second is due to the irreversible reduction of nonadsorbed molecules. This reaction involves a slow chemical step. The reduction results in the fission of the carbon‐sulfur bond. Another reaction is the hydrolysis of adsorbed molecules (in the absence of any charge‐transfer step), giving the nitrile of cinnamic acid. This compound is also formed in the range of the anodic wave of thiocinnamam

ISSN:1040-0397    

DOI:10.1002/elan.1140020109

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractUsing linear sweep polarography (LSP) in an acidic solution (pH 2.8) containing Au(III) ions andN‐allyl‐N′‐(sodium‐p‐phenylsufonate)thiourea (NTu), the product of the reaction between Au(III) and NTu (NDF) is reducible at the mercury electrode with two waves at about −0.40 and −0.95 V [versus the saturated calomel electrode (SCE)]. In the presence of excess chloride, the potential of the first wave shifts positively to −0.35 V. This forms the basis of a highly selective and sensitive method for gold. The linear range for gold is from 1 × 10−7to 3 × 10−M, and the detection limit is 5 × 10−8M (9 ppb). This method has been used for the determination of gold in ore samples, and the results agree well with values obtained by accepted procedures. Various electrochemical techniques were used to study the mechanism of the redox process. The reaction mainly involves the formation of C,C′‐di‐N‐allyl‐N′‐ (sodium‐p‐phenysulfonate)dithiodiformamidine (NDF). Unlike some explanations reported in the literature about the reduction of formamidine derivatives (containing an SS bond) on an Hg electuode, the electrode process for the first wave (−0.40 V) is ascribed to the reduction of the HgS film, which is caused by the reaction of Hg with adsorbed NDF. In the presence of excess Cl‐ ions, the mixed precipitation film of HgS·xHg2Cl2may be formed on the electrode surface and make the first wave shift to −0.35 V. The second wave

ISSN:1040-0397    

DOI:10.1002/elan.1140020110

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractThe electrochemical oxidation of sulfamerazine at a pyrolytic graphite electrode was studied in phosphate buffers with a pH ranging from 3.0 to 10.8. The 2e−, 2H+oxidation of this compound produces an azo product. A possible reaction scheme is proposed on the basis of the results of linear sweep and cyclic voltammetry, coulometry, spectral studies, and product identificatio

ISSN:1040-0397    

DOI:10.1002/elan.1140020111

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY

摘要:

AbstractThe environmentally persistent pesticidesp,p′‐DDT and dieldrin may be determined simultaneously using an indirect adsorptive stripping voltammetric procedure that takes advantage of the very different binding capabilities of the two materials toward added iron(II). The method has been applied to the determination of these organochlorines in Australian bovine fat samples by employing benzyltrimethylammonium methoxide as a digestion medium. The limits of detection are 0.4 ppb (forp,p′‐DDT) and 0.7 ppb (for dieldrin), and the relative standard deviations (for 10 determinations) are 7.4 and 10.1%, respe

ISSN:1040-0397    

DOI:10.1002/elan.1140020112

出版商:VCH Verlagsgesellschaft mbH    

年代:1990

数据来源: WILEY