摘要:

AbstractA new sensor is described consisting of a Nafion membrane to which a very fine gold square grid indicator electrode is mechanically pressed. A platinum counter and a Pt/air reference electrode are prepared on the membrane using a chemical plating method. Nitrogen dioxide was determined in air by reduction at −0.3V vs. Pt/air electrode (0.75 V vs. SHE). The response dependence on the NO2concentration was linear, with a sensitivity of 59 nA.ppm−1(42% rel. humidity). The time constant and the time required to attain 95% of the steady ‐state response were 2.2 and 10 s, respectively. The response was independent of the air flow rate, but increased linearly with increasing relative humidity. The sensor sensitivity decreased with time–the longer the sensor was in contact with NO2. The decrease amounted to ca. 5% per 24 hours during constant exposure to NO2. The indicator electrode can be reactivated by cyclic polarization. On the basis of the sensitivity attained, the indicator electrode can be considered as an array of microband ele

ISSN:1040-0397    

DOI:10.1002/elan.1140040202

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractA method that allows speciation and electrochemical detection of thallium in flowing solutions has been developed. Thallous ions are determined using oxidative detection at a platinum electrode in a sulphuric acid‐formic acid solution. In the presence of thallic ions, iiradiation of the solution with UV light induces the reduction of Tl(III) to Tl(I) which is subsequently detected as described above. Under these conditions total thallium is determined. Irradiation of the flowing solution is carried out within the detector flow cel

ISSN:1040-0397    

DOI:10.1002/elan.1140040203

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe redox processes of copper ions were studied by alternating current (ac) voltammetry and cyclic voltammetry in 0.5 M NaCl and NaClO4solutions. The studies were performed at different pH values in the presence of atmospheric oxygen or by the addition of H2O2to the process. In the case of copper ions in NaCl solution both in the presence of atmospheric oxygen and added H2O2, a catalytic current was observed. With cyclic voltammetry the current was in the cathodic direction in spite of having an anodic sweep. The key factor is the presence of chloride ions as in the NaClO4solution; the observed catalytic current peaks are much smaller. The mechanism for the observed redox processes of copper is proposed.

ISSN:1040-0397    

DOI:10.1002/elan.1140040204

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractAccording to the calculations, in the presence of equimolar concentrations of uranyl‐ion and hydrogen peroxide at 5

ISSN:1040-0397    

DOI:10.1002/elan.1140040205

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractAn automated system for on‐line monitoring of trace uranium, based on a flow‐through adsorptive stripping operation, is described. The on‐line formation of the uranium‐oxine complex is followed by its adsorptive accumulation and voltammetric quantitation at the downstream working electrode. About 10–60 runs can be made every hour with high reproducibility (RSD of 3–5%) and a detection limit of 0.7 μg/L. The dependence of the peak current on different experimental variables is reported. The sequence of events involved in the adsorptive stripping voltammetric cycle is controlled by a computer. Analogous on‐line monitoring of chromium (VI) are also reported with 36 runs/h (2.1% RSD), and detection limit of 1.5 μg/L. The system holds great promise for field

ISSN:1040-0397    

DOI:10.1002/elan.1140040206

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe shape of the current–voltage curves at a channel electrode have been calculated for the various situations of the catalytic (EC′) mechanism. In particular the halfwave potential and limiting current are found to be highly sensitive to the solution‐flow rate and to the concentrations of the mediator and substrate employed. These observations provide a ready method of unambiguously characterizing the different pat

ISSN:1040-0397    

DOI:10.1002/elan.1140040207

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractA copper‐based chemically modified electrode (CME) has been constructed and characterized for flow‐through amperometric detection of catechol, resorcinol, and hydroquinone. Novel potential dependence of the detector response was first obtained for these analytes at the Cu CME, where negative peaks together with positive ones were observed in one definite chromatogram using amperometric detection. Its advantages in chromatographic applications were demonstrated. From these observations it is proposed that the detector response was governed by formation of copper complexes with the solutes. A dynamic linear range over two orders of magnitude was obtained, when operating the detector at +0.10 V vs. SCE, from which ng detection limits were achie

ISSN:1040-0397    

DOI:10.1002/elan.1140040208

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe experimental results obtained in this study show that a thick‐film graphite sensor assembly (with a Pt counter and an Ag/AgCl reference electrode) can be conveniently fabricated by the photolithographic and screen‐print metallization techniques. This sensor has been successfully employed for quantitatively determiningL‐ascorbic acid concentration in aqueous solutions with reasonably good reproducibility. This sensor provides the possibility of developing a miniature size practical device for detecting ascorbic acid in biochemical processing, such as in food and drug production. The mechanistic aspects of the oxidation ofL‐ascorbic acid on optical pyrolytic graphite electrodes were further studied with a rotating OPG disk electrode in two different electrolyte solutions. It was found that the oxidation ofL‐ascorbic acid is more favored in pH = 7 solutions than in pH = 1 solutions although a common 2‐electron transfer pathway is applied in

ISSN:1040-0397    

DOI:10.1002/elan.1140040209

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractIn the cobalt(II)—thiocyanate—ascorbic acid solution (pH = 2.0), nitrite can form a ternary complex (CoSCNNO)+, which can be reduced at mercury electrode to −0.59 V (vs. SCE). The wave can be used for the polarographic determination of traces of nitrite in the concentration range of 1 × 10−8−8 × 10−7M (single sweep polarography), 1 × 10−7−4 × 10−5M (differential pulse polarography). or 1.5 × 10−6−2 × 10−4M (direct current polarography). The mechanism of the electrode process is studied by linear sweep voltammetry, DC polarography, cyclic voltammetry, double‐step chronocoulometry, and controlled potential coulometry. The polarographic wave is ascribed to the reduction of nitrogen monoxide in the complex to hydroxyamine. The procedure is used for the direct determination of

ISSN:1040-0397    

DOI:10.1002/elan.1140040210

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe electrochemical behavior of 3‐(p‐sulfamoylphenylhydrazono)‐2, 4‐pentanedione has been studied in the pH range 2.2–10.2. It was observed that sulfamoylphenylhydrazone undergoes electrooxidation as well as electroreduction at the surface of a pyrolytic graphite electrode (PGE). The oxidation or reduction peaks observed can be used for the detection of this compound. The products corresponding to both processes have been separated and characterized using IR, NMR, and mass spectra. The reaction pathways have been proposed to account for the voltammetric, coulometric and spectral

ISSN:1040-0397    

DOI:10.1002/elan.1140040211

出版商:VCH Verlagsgesellschaft mbH    

年代:1992

数据来源: WILEY