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Analytical and Bioanalytical Chemistry (v.367, #4)
ELACH 4 – Forum on Electroanalytical Methods Warnemünde, Germany, September 13 to 17, 1999
by Peter Gründler (pp. 307-307).
Sonoelectroanalysis – an overview by Andrew J. Saterlay; R. G. Compton (pp. 308-313).
The coupling of power-ultrasound with well established but under-exploited electrochemical stripping voltammetry has led to the emergence of a powerful new analytical technique – sonoelectroanalysis. Where classical electroanalytical techniques were plagued with electrode-fouling and/or sensitivity limitations, the introduction of ultrasound into the system has given great increases in analytical efficiency and substrate applicability, predominantly through enhanced mass transport and electrode surface activation. This revitalised analytical technology has been applied to a range of modern analytical problems, allowing sensitive determination of a wide number of analytes from a variety of otherwise hostile matrices, including copper in beer and blood, lead in wine, petrol and river bed sediment, vanadium in aqueous media, nitrite in egg and manganese in instant tea granules. This paper gives an overview of these recent advances.
LIGA-electrodes in voltammetric and spectroelectrochemical studies by L. Dunsch; Andreas Neudeck; Peter Rapta (pp. 314-319).
The advantages of lithographic-galvanic (LIGA) fabricated microstructured honeycomb electrodes are demonstrated for spectroelectrochemical cells with respect to the response time (the time necessary to generate the product in a sufficient layer thickness close to the electrode to be detectable by UV-Vis-NIR spectroscopy) and to the conversion of the redox system in solution under thin-layer conditions. Transmission UV-Vis-NIR spectroscopy for several electrochemical applications can be performed in a special spectroelectrochemical cell based on the LIGA electrode and the two quartz rods, forming the walls of the cell and conducting the light beam through the cell. They are limiting the diffusion layer at the structured part of the working LIGA electrode. These microstructured LIGA-electrodes can be used as well defined models of porous electrodes at which redox processes occur under finite diffusion conditions. Such electrodes have been successfully used in the voltammetric and spectroelectrochemical study of various redox systems in both aqueous and non-aqueous solvents. The possibility to fabricate the well defined microstructures from various organic conducting polymers is demonstrated by the electrochemical deposition of polypyrrole in moulded LIGA-forms at high current densities in aqueous solutions.
Basics of temperature pulse voltammetry by T. Voß; Andreas Kirbs; Peter Gründler (pp. 320-323).
A new electrochemical technique is presented that allows peak-shaped voltammograms to be recorded at local temperature values from room temperature to above boiling point. This new method, temperature pulse voltammetry (TPV), is analogous to differential pulse voltammetry (DPV), but makes use of temperature jumps instead of potential pulses. Fundamentals are presented and potentialities demonstrated. As an example, ferrocyanide is investigated using a new kind of heated electrode on the basis of screen-printed gold layer structures on low-temperature cofired ceramics (LTCC) substrates.
Phenomena at hot-wire electrodes by P. Gründler (pp. 324-328).
An overview is given describing phenomena at heated microelectrodes where matter and heat energy are simultaneously emitted into the solution. With controlled electric heating, virtual “quiescent” periods as well as ones with constant streaming conditions are found that depend on the heating time. A close look at a permanently heated wire reveals a well defined structure with stationary concentration, temperature and flow rate profiles. The observed phenomena can be utilised for analytical measurements, e.g. with the novel method “Temperature Pulse Voltammetry” (TPV).
Photocurrent measurements for laterally resolved interface characterization by W. Moritz; I. Gerhardt; D. Roden; M. Xu; S. Krause (pp. 329-333).
A miniaturized optical set-up based on a CD-ROM player optic was developed for LAPS (light addressable potentiometric sensors). A focus of 2.6 μm was achieved using this easy to handle device. The lateral resolution of LAPS measurements can be improved by using GaAs as the semiconductor material instead of Si. The diffusion length of the minority charge carriers was determined to be smaller than 3.1 μm. A new method called SPIM (scanning photo-induced impedance microscopy) is described. Using this technique, the impedance of thin films can be measured with lateral resolution.
Electrochemical surface analysis with the scanning droplet cell by M. M. Lohrengel; A. Moehring; M. Pilaski (pp. 334-339).
A new electrochemical device, the scanning droplet cell, is presented. Small electrolyte droplets are positioned on the sample surface and enable a spatially resolved surface analysis or modification. The droplet is simply held by its surface tension and, therefore, no surface pretreatment is necessary. According to the conventional 3-electrode arrangement all common potentiostatic and galvanostatic techniques, e.g. impedance spectroscopy, cyclic voltammetry, or current transients of potentiostatic steps, are possible.
Reference electrodes based on conducting polymers by Klaus-Michael Mangold; Sabine Schäfer; K. Jüttner (pp. 340-342).
Several attempts to produce conducting polymer based all-solid-state reference electrodes are presented. Open circuit potential of conducting polymers is redox sensitive and Donan equilibrium dependent. Therefore, more sophisticated constructions are necessary. Most promising were bilayers composed of conducting polymers with different ion-exchanger properties.
Corrosion protection by the organic metal polyaniline: results of immersion, Volta potential and impedance studies by J. Posdorfer; Bernhard Wessling (pp. 343-345).
Properties of the new polyaniline containing primer CORRPASSIV™ sealed with two different top coats are characterised and compared with top coated samples using no or a conventional zinc-rich primer. Measurements were made using scanning Kelvin-probe (SKP), electrochemical impedance spectroscopy (EIS), voltammetry and analysis of iron and zinc content in electrolytes for testing. Results are presented and the powerful corrosion protection using the organic metal is shown.
Investigation of ion-bombarded conducting polymer films by scanning electrochemical microscopy (SECM) by G. Wittstock; Tim Asmus; Thomas Wilhelm (pp. 346-351).
Scanning electrochemical microscopy (SECM) was used to investigate the effect of ion bombardment on thin films of the conducting polymers poly[3-ethoxy-thiophene] (PEOT) and poly[ethylenedioxy-thiophene] (PEDT). Bombardment with Ar+-ions converts the topmost 30 nm thick layer to an essentially insulating material. SECM approach curves as well as two dimensional scans prove the existence of regions of different conductivity within the irradiated regions that did not show a significant dependence on ion dosage. PEDT layers patterned by ion bombardment through microscopic masks are investigated as prototypes of miniaturized printed circuit boards that can be formed by galvanic copper deposition onto conducting PEDT. Defects in conducting polymer patterns were analyzed by SECM imaging before any deposition of copper. Appropriate representations of SECM images for the evaluation of this technologically important question are discussed.
Imaging the activity of nitrate reductase by means of a scanning electrochemical microscope by J. Zaumseil; G. Wittstock; S. Bahrs; P. Steinrücke (pp. 352-355).
Scanning electrochemical microscopy (SECM) was used to characterize immobilized nitrate reductase (NaR) from Pseudomonas stutzeri (E.C. 1.7.99.4). Nitrate reductase with membrane fragment was embedded in a polyurethane hydrogel in a capillary and solubilized NaR without membrane fragment was covalently coupled to a diaminoethyl-cellulose-carbamitate film on glass. After systematic studies of possible mediators, SECM feedback imaging of both forms of immobilized NaR was accomplished with methylviologen as redox mediator.
Total determination of metal-binding carbohydrates in plant extracts by using FIA with electrochemical detection by G. Weber; J. Messerschmidt (pp. 356-358).
FIA with pulsed amperometric detection (PAD) is used for the determination of metal-binding carbohydrates in plant extracts. Results of direct FIA measurements agree very well with those of corresponding HPLC-PAD analyses. The proposed method is used to determine total carbohydrates in isolated low-molecular-weight fractions of plant roots, which have been obtained after extraction at different pH values. The results are compared with those obtained by corresponding metal determinations (Ca, Mg, Zn, Mn) by AAS and also with constant potential amperometric detection at a copper working electrode. The latter detection mode is more sensitive, but less selective for carbohydrates.
Analysis of illicit drugs by nonaqueous capillary electrophoresis and electrochemical detection by Ulli Backofen; Frank-Michael Matysik; Werner Hoffmann; C. E. Lunte (pp. 359-363).
Nonaqueous capillary electrophoresis (NACE) was applied to the determination of illicit drugs. The complete separation of amphetamine, methamphetamine, 3,4-methylene dioxy amphetamine (MDA), 3,4-methylene dioxy methamphetamine (MDMA), mescaline, cocaine and benzoylecgonine was obtained using an acetonitrile based buffer solution containing 10 mM sodium acetate and 1 M acetic acid. Electrochemical detection using a Pt microdisk electrode set to a potential of +1.8 V was found to be selective for MDA, MDMA and mescaline. The detection limits for these compounds were in the low ng/mL range which is between 2 and 3 orders of magnitude lower compared to UV-detection.
Modified screen-printed electrodes for the investigation of the interaction of non-electroactive quinazoline derivatives with DNA by J. Labuda; M. Bučková; S. Jantová; I. Štepánek; I. Surugiu; B. Danielsson; M. Mascini (pp. 364-368).
Five morpholino-quinazoline derivatives have been investigated voltammetrically using a competition with the tris(o-phenanthroline) cobalt(III) redox marker for the accumulation at dsDNA modified screen-printed electrodes. An association of quinazolines with DNA was observed at the modified electrodes polarized by the negative potential of –0.4 V vs. Ag/AgCl. This was confirmed by a potentiometric stripping analysis based on the DNA guanine signal. Calibration curves for quinazolines within a concentration range of μmol/L were obtained with DP voltammetry using 5 × 10–7 mol/L Co(phen)3 3+ marker. The quinazolines exhibit no effect on the DNA complex with the fluorescent thiazole orange derivative TO-PRO-3. The role of the accumulation potential in the association interaction with DNA is discussed.
Determination of gold using clay modified carbon paste electrode by Z. Navrátilová; Petr Kula (pp. 369-372).
Sorption of gold(III) chlorocomplexes was studied by means of a carbon paste electrode modified with montmorillonite. Anionic exchange behavior was found in chloride media with low ionic strength. Anionic sorption of [AuCl4]– can be used as a preconcentration step to the determination of Au(III). Linear calibration dependences were found in the concentration range 4.06 × 10–6– 1.22 × 10–5 mol/L Au(III) after 5 min of sorption and in the range 8.12 × 10–7– 6.1 × 10–6 mol/L after 10 min of sorption. Interferences of several anions and cations were studied. Model samples of table water were analyzed.
Voltammetric determination of copper at chemically modified electrodes based on crown ethers by V. S. Ijeri; A. K. Srivastava (pp. 373-377).
The feasibility of fabricating copper-sensitive chemically modified electrodes (CMEs) for trace analysis in aqueous and in 40% (v/v) ethanol-water media was investigated. Carbon paste electrodes modified with crown ethers were constructed by mixing the crown ethers into a graphite powder-paraffin oil matrix. The electrodes so formed were able to bind Cu(II) ions chemically and gave better voltammetric responses than the unmodified ones. The crown ethers studied and compared were 15-crown-5, benzo-15-crown-5 and dibenzo-18-crown-6. With a 3% benzo-15-crown-5 CME, Cu(II) could be quantified at sub-ppm levels by differential pulse voltammetry with a detection limit of 0.05 ppm. By differential pulse anodic stripping voltammetry Cu(II) could be quantified over the range 1 to 100 ppb. Interference from metal ions like Ni(II), Co(II), Mn(II), Fe(II), etc. have also been studied. The method was successfully applied to artificial as well as commercial samples of alcoholic beverages.
Simultaneous determination of Cd, Pb, Cu, Sb, Bi, Se, Zn, Mn, Ni, Co and Fe in water samples by differential pulse stripping voltammetry at a hanging mercury drop electrode by M. M. Ghoneim; A. M. Hassanein; E. Hammam; A. M. Beltagi (pp. 378-383).
A highly sensitive and selective voltammetric procedure is described for the simultaneous determination of eleven elements (Cd, Pb, Cu, Sb, Bi, Se, Zn, Mn, Ni, Co and Fe) in water samples. Firstly, differential pulse anodic stripping voltammetry (DPASV) with a hanging mercury drop electrode (HMDE) is used for the direct simultaneous determination of Cd, Pb, Cu, Sb and Bi in 0.1 M HCl solution (pH = 1) containing 2 M NaCl. Then, differential pulse cathodic stripping voltammetry (DPCSV) is used for the determination of Se in the same solution. Zn is subsequently determined by DPASV after raising the pH of the same solution to pH 4. Next, the pH of the medium is raised to pH 8.5 by adding NH3/NH4Cl buffer solution for the determination of Mn by DPASV. Ni and Co are determined in the same solution by differential pulse adsorptive stripping voltammetry (DPAdSV) after adding DMG (1 × 10–4 M). Finally, 1 × 10–5 M 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) is added to the solution for the determination of Fe by DPAdSV. The optimal conditions are described. Relative standard deviations and relative errors are calculated for the eleven elements at three different concentration levels. The lower detection limits for the investigated elements range from 1.11 × 10–10 to 1.05 × 10–9 M, depending on the element determined. The proposed analysis scheme was applied for the determination of these eleven elements in some ground water samples.
Microarrayelectrodes for voltammetric and amperometric detection of organic pollutants by J. Schwarz; Heiner Kaden (pp. 384-387).
Disk and band shaped microarrayelectrodes (MAE) of gold and carbon have been developed. These electrodes can be used for electrochemical detection of different organic pollutants in organic and aqueous media. Differential pulse voltammetric, cyclic voltammetric and amperometric investigations at these MAE in stationary and flowing solutions with selected pesticides, polyaromatic hydrocarbons (PAH) and phenols have been carried out.
Basic investigations on zeolite application for electrochemical analysis by O. Schäf; H. Ghobarkar; A. C. Steinbach; U. Guth (pp. 388-392).
Basic investigations on the electrochemical behavior of alumosilicate zeolites were conduced in gas atmosphere and aqueous solution using impedance spectroscopy under in situ conditions where “zeolitically” bound water molecules are present in the channel and cage system. Natural stilbite (STI) and heulandite (HEU), zeolites of structure types with the same 4 – 4 = 1 building units, were used for these investigations. At a given temperature, well defined water partial pressures were applied in the gas atmosphere (in situ conditions) and the effect of polar organic molecules on conductivity was investigated. Furthermore, the effect of complete water saturation of the channel system on the Arrhenius type activation energy of conductivity was investigated in aqueous solution in comparison. The ion-exchange behavior of zeolite materials could be monitored under these conditions. These results show that, dependent on the different parameters affecting the zeolite conductivity behavior, they are applicable in the field of electrochemical analysis if these basic results on single crystals are transferable to polycrystalline materials.
Screen-printed copper ion-selective electrodes by R. Koncki; Łukasz Tymecki; Elżbieta Zwierkowska; Stanisław Głąb (pp. 393-395).
A simple, low-cost and reproducible method for the mass production of potentiometric ion-selective electrodes for copper ions is presented. These planar, strip sensors were obtained by screen-printing. The application of pastes cured at low temperature allows printing of the sensors on low-cost, plastic substrates. The pastes for printing of ion-sensitive thick-film membranes were based on copper (I) and copper (II) sulfides. The analytical characteristics of the thick-film electrodes were compared. The analytical properties (range of determination, sensitivity, selectivity, response time) of the copper (I) sulfide-based sensors were comparable with those for conventional ion-selective electrodes.
Development of miniaturized potentiometric nitrate- and ammonium selective electrodes for applications in water monitoring by J. Schwarz; Heiner Kaden; Guntram Pausch (pp. 396-398).
Mobile analysis with potentiometric sensors is well suited for field measurements. Ion-selective electrodes (ISE) based on polymeric membranes for in-situ determination of nitrate and ammonium contents in ground water, drinking water and surface water have been developed. The ISE are integrated in a multisensor module (MSM) for monitoring these ions over longer time intervals. The receptor is a PVC-membrane with tridodecylammonium nitrate (TDDA) for nitrate- and nonactine for ammonium-electrodes as ionophores. As plasticizer dibutylphthalate (DBT) was used. The main parameters for assessing the efficiency of these ISE are presented.