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Analytical and Bioanalytical Chemistry (v.362, #2)
Theory and practice of sensors with hot-wire electrodes by P. Gründler (pp. 180-183).
The possibilities and applicability of electrochemical sensors with heated electrodes are overviewed. A theory for such devices is developed, including the interactions between the heating alternating current and the electrochemical cell and the measuring circuit, as well as calculation of the temperature expansion. Experimental details on the circuitry and the electrode design are given, and results are presented for some analytical applications.
Development of renewed mercury multi-purpose (multi-mode, versatile) microelectrodes, a part of PC-controlled measuring systems (including the PC-ETP) by Ladislav Novotný (pp. 184-188).
Information is given about the development of renewed miniaturized mercury multi-purpose (multi-mode) electrodes as an inseparable part of the development of modern polarography and voltammetry; casette-type, pen-type and PC-controlled systems, incl. the polarographic/voltammetric set. According to the experimental behavior and ranges of their radii the regimes of renewed stationary mercury electrodes are divided into three categories – mini-, semimicro- and microelectrodes (mE, sμE and μE). Their spontaneously growing, stepwisely growing, stationary and contracting (compression) modes are schematically outlined. Information on basic functional properties of the discussed renewed mercury semimicro- or microelectrodes using meniscus and microdrop-electrodes, by means of the d. c., anodic stripping and adsorptive stripping voltammetry is given.
Capillary batch injection analysis and capillary flow injection analysis with electrochemical detection: a comparative study of both methods by U. Backofen; F.-M. Matysik; W. Hoffmann; H.-J. Ache (pp. 189-193).
Capillary batch injection analysis (CBIA) and capillary flow injection analysis (CFIA) in combination with electrochemical detection as well as optical detection methods were studied and compared with respect to their performance. Despite the differences in technical equipment both techniques share the same idea of reproducible transport and washout of nanolitre samples over sensing surfaces. Thus the same electrochemical flow cell can be used for both CBIA and CFIA. The amperometric and potentiometric CBIA responses were studied under various experimental conditions in order to optimise the CBIA set-up. In particular, the density of the sample solution relative to that of the cell electrolyte had a remarkable effect on the hydrodynamic characteristics of CBIA. Dispersion in CFIA was investigated using on column UV-detection for electroosmotic flow (EOF) conditions as well as for gravity flow conditions. It is demonstrated for a 75 μm capillary that the relative band broadening of the sample plug under gravity flow is only about twice as large as under EOF. Furthermore, dispersion in a system that involves a chemical reaction between the sample and the carrier solution, namely CrO7 2– and Fe2+ has been investigated by amperometric detection and exploited for the determination of dichromate microsamples.
Amperometric determination of hydrogen peroxide with a manganese dioxide film-modified screen printed carbon electrode by Klemens Schachl; Hailemichael Alemu; K. Kalcher; Helmut Moderegger; Ivan Svancara; Karel Vytras (pp. 194-200).
A carbon thick film electrode modified with an MnO2-film is investigated as an amperometric detector for hydrogen peroxide in flow-injection analysis (FIA). At an operating potential of +0.48 V vs. Ag/AgCl catalytic oxidation of the analyte is exploited for amperometric monitoring. Experimental parameters, such as pH of the carrier, working potential, flow rate and injection volume, are optimized. The amperometric signals are linearly proportional to the concentration of H2O2 in the range from 0.005 to 10 mg/L, showing a detection limit (3σ) of 2.3 μg/L. The method is applied to the determination of H2O2 in rain water and to a simple assay to quantify glucose in human plasma.
Flow-through stripping chronopotentiometry for the monitoring of mercury in waste waters by E. Beinrohr; J. Dzurov; J. Annus; J. A. C. Broekaert (pp. 201-204).
A simple method for the determination of total mercury in waste waters is described. It makes use of a flow system incorporating a wall-jet cell equipped with a gold working electrode. The untreated sample is mixed on-line with the acidic carrier electrolyte which contains potassium permanganate and transforms the various species of mercury, especially elementary Hg, to Hg(II). The pre-treated solution enters the cell where mercury is deposited on the gold electrode. In the next step the deposit is stripped at constant current and the time corresponding to the dissolution of the deposit is obtained from the chronopotentiometric signal. The method enables it to determine and monitor Hg in the concentration range of 1 to 1000 μg/L in 5 min intervals.
Determination of nifuroxazide with polarography and adsorptive stripping voltammetry at mercury and carbon paste electrodes by W. Buchberger; G. Niessner; R. Bakry (pp. 205-208).
A simple method for the determination of the urinary tract antibiotic nifuroxazide has been developed. The electrochemical reduction of the nitro group at mercury and carbon paste electrodes can be used for the determination with and without adsorptive preconcentration. The influence of parameters like pH of the background electrolyte, preconcentration potential and preconcentration time on the sensitivity of the method has been studied. Modification of the carbon paste by addition of nonpolar polystyrene/divinylbenzene particles has been investigated to enhance the adsorption properties of the surface. Concentrations as low as 10 ng/mL could be determined in urine without interferences.
Characterization of low-molecular-weight metal species in plant extracts by using HPLC with pulsed amperometric detection and cyclic voltammetry by G. Weber; F. Alt; J. Messerschmidt (pp. 209-214).
An analytical separation scheme is presented for the isolation of low-molecular-weight metal species (< 10 kDa) in plants. After ultrafiltration of the aqueous plant extracts isotachophoresis or gel chromatography is used for pre-separation and HPLC at a cyclodextrin-phase for further separation of metal containing fractions. Trace metals are detected off-line by using either adsorptive stripping voltammetry for platinum or AAS for zinc and magnesium. It is shown that platinum and zinc detection closely correlate with pulsed amperometric detection (PAD), while magnesium behaves differently. PAD is carried out after post-column addition of sodium hydroxide, thus enabling a sensitive and selective detection of carbohydrates. It is demonstrated that cyclic voltammetry is a useful tool for further characterization of the PAD-detectable metal species. By comparison of the cyclic voltammograms of carbohydrate standards, including carbohydrate-metal species, with the respective voltammograms obtained from HPLC fractions, carbohydrate species isolated from the samples can be considered as being either partly oxidized sugars (sugar alcohols or sugar acids) or glycosidically bound sugars.
Miniaturized sensor module for in-situ control of waters by S. Herrmann; W. Vonau; F. Gerlach; H. Kaden (pp. 215-217).
A new sensor module is developed for the in-situ control of waters, especially surface waters. Complex miniaturized sensor technology is used for the determination of the parameters pO2, pH, pNO3, pCl, pPO4, pNH3 or pNH4 and conductivity. Miniaturization of sensors results in small sample volumes and small volumes of calibration solution required. Results of testing this sensor module are described. The special features of this apparatus are its compact construction and its optimum functioning capability under flow conditions.
Capillary electrophoretic separation of inorganic and organic arsenic compounds by H. Greschonig; M. G. Schmid; G. Gübitz (pp. 218-223).
Capillary zone electrophoresis was used to separate arsenite, arsenate, dimethylarsinic and diphenylarsinic acid, methanearsonic acid, phenyl- and p-aminophenyl arsonic acid, phenylarsineoxide and phenarsazinic acid. Anionic and uncharged species were separated in a fused silica capillary with on-column UV detection at 200 nm. A 15 mM phosphate solution adjusted to pH 6.5 containing 10 mM sodium dodecylsulfonate served as background electrolyte. The influence of pH and applied voltage on separation efficiency, as well as the feasibility of identification of arsenic compounds in spiked urine, were investigated.
Anodic stripping voltammetric determination of thallium as [TlBr4]-rhodamine B complex by D. Bohrer; G. Schwedt (pp. 224-229).
The anodic stripping voltammetric behaviour of the [TlBr4]-rhodamine B complex is described and compared with that of thallium(I) and thallium(III) ions. The electrolyte composition, the best potential for the deposition of thallium from the complex in the selected electrolyte, the duration of the electrolysis, and the possibility of reduction of thallium in the [TlBr4]-rhodamine B complex before the electrolysis with ascorbic acid were investigated. The results showed good reproducibility of the measurements of thallium as [TlBr4]-rhodamine B complex and are similar to those obtained for thallium as Tl(I) and Tl(III) ions. As the [TlBr4]-rhodamine B complex is strongly adsorbed on polyethylene, a previous preconcentration step on a column, packed with polyethylene powder, allowed the voltammetric determination of thallium as [TlBr4]-rhodamine B complex in samples of KCl and NaCl as solid salts after the separation of the matrix. With this procedure it was possible to reach enrichment factors of 25 with recoveries from 96.7 to 107.9% for thallium concentrations from 5 to 40 μg L–1 and RSD between 4.2 and 9.2%. The procedure was used to determine thallium traces in KCl and in sea salt. The results of these determinations were compared with the results obtained by graphite furnace atomic absorption spectrometry.
Flow injection analysis of fluoride in electroplating baths with potentiometric detection by R. Pérez-Olmos; M. B. Etxebarria; J. L. F. C. Lima; M. C. B. S. M. Montenegro (pp. 230-233).
A high dispersion FIA system with a fluoride selective and a double junction reference electrode in cascade arrangement was developed for the determination of the fluoride content in chromium electroplating baths. The analyses of seven synthetic baths prepared in the laboratory and two samples provided by the industry gave results with a mean recovery value of 100.5%, and a mean variation coefficient of 1.6%. These data were better than those obtained by the EDTA complexometric titration, the reference technique, with a mean recovery of 94.0% and a mean variation coefficient of 7.5%. The sampling rate for the FIA manifold was 20 samples per hour.
Amperometric determination of ascorbic acid at a novel ‘self-doped’ polyaniline modified microelectrode by Jing-Juan Xu; Dong-Mei Zhou; H.-Y. Chen (pp. 234-238).
A ‘self-doped’ polyaniline modified microelectrode, prepared by cyclic potential sweep on a microdisk gold electrode from –0.2 to 0.85 V in 0.5 mol/L sulfuric acid containing aniline and o-aminobenzoic acid, has been developed. The copolymerized process and the resulting polymer characteristics were investigated in detail. This composite film indicated a good electrochemical activity in a wide pH range even in basic solution. Meanwhile, the redox couple exhibited an excellent electrocatalytic activity for the oxidation of ascorbic acid. The oxidation overpotential of ascorbic acid was decreased over 200 mV at this modified electrode compared with a bare gold one. Moreover, the effects of film thickness and pH on the catalytic efficiency were further studied. The dependence of catalytic currents on the concentration of ascorbic acid was linear in the range of 1.2 × 10–5∼ 2.4 × 10–3 mol/L with a correlation coefficient of 0.996. Also, the determination of ascorbic acid in actual samples was evaluated and the results are satisfactory.