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Aus langjahriger Erfahrung ergibt sich, dass die Aurikulomedizin in der Lage ist, eine Hilfestellung fur die Diagnose und Therapie der Multiplen Sklerose zu geben. Dabei wird fur die Diagnose das PC-gesteuerte Frequenzhammerchen und fur die Therapie die Applikation RemedyMaster® fur iPads angewandt. Die Praxis zeigt, dass schubweise Verlaufe zum Stillstand kommen und die Krankheit nach den Kriterien der Aurikulomedizin praktisch immer abklingt. Diese wirksame und nebenwirkungsfreie Therapie stellt fur die Patienten eine grose Hilfe dar.

Durch Kombination zweier Frequenzen bei der Untersuchung lasst sich nahezu jedem gefundenen Punkt eine Ursache = Kausalitat zuordnen. Dies eroffnet zusatzliche Therapiemoglichkeiten. Neben dem Frequenzhammerchen fur die Diagnose kommt elektronisch generierten Informationen fur die Therapie eine besondere Bedeutung zu.

In situ electron spin resonance (ESR) spectroelectrochemical and thermoelectrochemical studies of the non-substituted α - and the alkyl substituted (in α , ω -positions) sexithiophenes as single molecules in solution are presented. Thus any influence of interactions of the molecules in the solid state is avoided. In nitrobenzene solution the life time of the cation radicals is sufficiently high to detect and characterize them by in situ ESR spectroscopy. Furthermore, the α -sexithiophene ( α -6T) was found to form insoluble films at the electrode surface by dimerization and polymerization while no film deposition at the electrode was detected for the end-capped α , ω -dihexylsexithiophene (DH-6T). In thermoelectrochemical experiments with continuous heating during anodic polarization, the polymer formation appears to be completely stopped. Obviously, the thermal stirring prevents the deposition of the generated polymer at the heated surface. The voltammetric waves corresponding to the radical cation or even the dication formation keep maintained in CV with permanent heating as well as with temperature-pulse voltammetry (TPV). With heating pulses being too short to initialize convection, the behavior was found different from that with permanent heating. Here, the polymerization at room temperature even with a somewhat increased rate causes a film formation at the electrode.

The determination of the actual electrode surface temperature is important for all electrochemical methods using in situ heating of electrodes. Existing methods of temperature measurement of a heated thin-wire electrode are of restricted use and critically discussed in the introduction. The use of the electrode wire itself as a resistive thermometer is improved in the present method. With the new thermoelectrochemical method temperature pulse voltammetry, the reliability of different thermometric methods can be compared. In this way, it is ensured to have correct temperature measurements at wire microelectrodes in all common solvents available.

Thermoelectrochemistry as a branch of electrochemistry like photoelectrochemistry is reviewed in an integral treatment of the subject. Especially modern thermoelectrochemistry is focused on new techniques to vary the temperature as an independent variable. This review based on a definition of modern thermoelectrochemistry includes all the classical work which contributes to the formation of modern thermoelectrochemistry, among them high-temperature electrochemistry, subcritical- and supercritical electrochemistry and in-situ electrochemical calorimetry. The main focus is on modern techniques like fast electrode heating by lasers or by alternating current as well as on heating of solution spots by microwaves and related methods. Here the state of the art in modern thermoelectrochemistry is critically reviewed for the first time.

An instrument for electroanalysis extended to thermoelectrochemical studies is presented here consisting of easily available components. An analog potentiostat is combined with a microcontroller. The latter is controlled by an Excel sheet extended by macros written in VBA (visual basic for applications). The worksheet acts as a virtual instrument with front panel and command buttons. Thus, specialized, expansive measuring software packages are unnecessary. The design of new techniques is facilitated by a of graphical representation of pulse sequences or the exciting waveforms. The instrument has proved to be useful for design and performance of non conventional electrochemical techniques working with additional parameters like irradiation or heat. Examples are given for thermoelectrochemical measuring sequences like TPV (temperature pulse voltammetry).

Biosensors based on DNA and DNA-carbon nanotubes film immobilized at the surface of a screen-printed carbon electrode were used for simple in vitro tests of chemical toxicity. The damage to DNA caused by tin(II) and arsenic(III) compounds as components of specific reaction media was evaluated by means of an electrochemical DNA marker, [Co(phen) 3 ] 3+ , as the portion of original dsDNA which survives an incubation of the biosensor in the cleavage medium. The results were confirmed by the electrically heated electrode and by the measurement of the DNA guanine moiety signal.

Indirectly heated electrodes operating in a non-isothermal mode have been used as transducers for reagentless glucose biosensors. Pyrroloquinoline quinone-dependent soluble glucose dehydrogenase (PQQ-sGDH) was entrapped on the electrode surface within a redox hydrogel layer. Localized polymer film precipitation was invoked by electrochemically modulating the pH-value in the diffusion zone in front of the electrode. The resulting decrease in solubility of an anodic electrodeposition paint (EDP) functionalized with Osmium complexes leads to precipitation of the redox hydrogel concomitantly entrapping the enzyme. The resulting sensor architecture enables a fast electron transfer between enzyme and electrode surface. The glucose sensor was operated at pre-defined temperatures using a multiple current-pulse mode allowing reproducible indirect heating of the sensor. The sensor characteristics such as the apparent Michaelis constants K(M)(app) and maximum currents I(max)(app) were determined at different temperatures for the main substrate glucose as well as a potential interfering co-substrate maltose. The limit of detection increased with higher temperatures for both substrates (0.020 mM for glucose, and 0.023 mM for maltose at 48 degrees C). The substrate specificity of PQQ-sGDH is highly temperature dependent. Therefore, a mathematical model based on a multiple linear regression approach could be applied to discriminate between the current response for glucose and maltose. This allowed accurate determination of glucose in a concentration range of 0-0.1mM in the presence of unknown maltose concentrations ranging from 0 to 0.04 mM.

We describe a novel instrument and electrical circuit for sensitive electrochemical measurements at simultaneous direct electrode heating. The new measuring principle can be applied to working electrodes of various designs featuring two end contacts. In our experiments, the contacts were connected to a 100 kHz AC heating power supply and the potentiostat via the new inductor bridge circuit. A compact heating-generator housing contains all components necessary for sine wave generation as well as amplification and transformation of the heating power. The new arrangement yields high temperature cyclovoltammetric signals for the [Fe(CN)6]3−/4− redox system with a noise level superior to the earlier symmetrically branched wire electrode designs. Noise and disturbances are dramatically suppressed especially for high resistance electrodes such as glassy carbon electrodes. Without a center contact, the working electrode design is greatly simplified. This opens new opportunities for the design of a great variety of heated electrodes that may be arranged in arrays or consist of materials with relatively high resistivity such as carbon and conducting polymers.

This communication reports about preliminary studies of self-assembled monolayers (SAMs) on bismuth bulk electrodes (BiBEs) using daunomycin and picric acid as electrochemical indicators. The cyclic voltammetric signals of these indicators decreased after the modification of the bismuth electrode with alkanethiols, indicating the formation of SAMs on bismuth. Signal decrease as well as the stability of the SAMs depends strongly upon the length of the alkanethiol. The bismuth-based SAMs were significantly more stable at negative potentials than SAMs on a gold substrate, yielding an useful potential range from −0.3 V to −1.3 V. Such highly stable SAMs could be beneficial for trace metal detection and biosensors. Keywords: Bismuth bulk electrode, Self-assembled monolayer, SAM, Voltammetry, Daunomycin, Picric acid

This article reviews the development of the various heated electrodes, heating devices and their analytical applications which have been published during the last decades. Generally spoken, electrode heating can provide different positive effects on electrochemical measurements: mass transport enhancement, reaction kinetics acceleration and the removal of deposited substances from the electrode surface. This often leads to remarkably improved signal-to-noise characteristics in electroanalytical chemistry. Short heat pulses or direct heating of very small electrolyte compartments allow for temperatures far above the boiling point of the solution. Major application fields include trace metal and nucleic acids analysis. Future development will result in miniaturized selectively heated electrode arrays.

The flow of thermodynamic quantities, preferably entropy, from a heated region to the colder bulk solution, has been discussed in Chap. 2. Thermodynamic quantities cannot be measured directly but have to be calculated. For practical purposes, knowledge of measurable quantities is more interesting. In an electrochemical experiment with heated electrode–solution interfaces, two streams across the interface can be stated, namely heat and matter. Heat is transported since hot and cold zones are in contact, and also to a much lower extent, by reaction heat. Matter is transported as a result of electrochemical processes which give rise to generate or to consume electroactive particles, respectively, as soon as a current is flowing. As a result, two profiles will form near to the interface. We can expect a profile T = f(x), the temperature profile, and c = f(x), the concentration profile. The symbol x denotes the distance from the hottest place. Both profiles can be calculated as given below, and both are very important for the interpretation of electrochemical results in cells with heated interfaces. Knowledge of the profiles can answer important questions, among them the question which maximum temperature can be obtained with a given heating arrangement or the question how the thermal stirring effect is affecting the shape of voltammograms.

Experiments with indirect electrode heating can be done without any special precautions and with all the common equipment available for electrochemical investigations. Additionally, there is necessary only some kind of heating power supply. Commercial units are suitable and even simple line transformers have been utilised. With indirect heating, it does not matter whether DC or low frequency AC is applied.

Classical industrial processes like electrodeposition, galvanising, or electrochemical oxidation of materials are temperature dependent. Traditional processing takes place in open cells. Consequently, many “trivial” thermoelectrochemical investigations in open cells, at moderate temperature variation, have been described. The majority of such studies are dedicated to the improvement of efficiency [1–26]. Deposition of metals, among them copper [1, 2], zinc [3–5], nickel and its alloys [6, 7], chromium [8] and cobalt [9, 10] has been studied. Also electrochemical generation of oxide layers on zinc and on aluminium [4, 12] was subject of papers. Temperature dependence of less common phenomena, e.g., calcareous scaling [13], electrostimulated leaching of minerals [14, 15] or growth of nanocables [16] has been studied. Classical thermoelectrochemical experiments provided information about important partial processes as hydrogen electrosorption [17] or lithium ion intercalation into graphite [18]. Deposition processes have been investigated by means of the electrochemical quartz microbalance under temperature variation [19]. Uncommon electrode materials were single crystal platinum [20] and diamond electrodes [21], as well as paste electrodes made of graphite and ionic liquids [22]. Ionic liquids as solvents have been applied in open cells at moderate temperature variation [23, 24]. An interesting application of classical thermoelectrochemistry dealt with a process named electrodialysis [25].

This paper reports on the electrochemical behavior and determination of nicotinamide adenine dinucleotide reduced (NADH) at indirectly electrically heated platinum electrodes. At room temperature, a surface fouling can be observed during voltammetric and amperometric measurements, whereas a slight electrode heating during the measurements greatly minimizes such electrode passivation. This is illustrated by repetitive cyclic and square-wave voltammetric scans as well as using amperometry. The effect of electrode temperature and NADH concentration is evaluated. Amperometric calibration data exhibit a 10-fold higher sensitivity upon elevating the electrode temperature from 22 to 75 °C. Furthermore, the amperometric response at the hot Pt-electrode is very stable, with 86% of the initial activity remaining after 20 min stirring of 5 mM NADH (compared to 32% under cold conditions). This represents the first example of using heated electrodes for minimizing surface fouling effects. The ability of heated Pt-electrodes to promote the NADH electron-transfer reaction suggests great promise for dehydrogenase-based amperometric biosensors.

This paper describes how the surface of an oil–graphite based carbon paste electrode (CPE) can be studied by means of atomic force microscopy (AFM). By choosing the scanning parameters very carefully, it is possible to scan even such a soft and delicate surface. Both intermittent contact and phase shift scan modes provide useful information about nano-distribution of topographical details as well as hard and soft areas on the surface. The electrochemical bismuth film deposition from a 0.05 M sulphuric acid +1 ppm Bi(III) containing electrolyte can be investigated by both scan modes. Intermittent scan mode yields very thin (2 nm) layer-shaped structures sizing from 20 nm to some microns. Phase shift scans of the same sections depict extensive areas of high and uniform phase shift, which cannot be found on the bare CPE, and thus have to be attributed to the newly formed bismuth film. AFM holds great promise for the investigation of all kinds of carbon paste electrodes. Keywords: Carbon paste electrode, CPE, Bismuth film electrode, BiFE, Atomic force microscopy, AFM

DNA hybridization plays an important role in medical diagnostics, drug development and biological threat discovery. Despite the wide use of optical hybridization detection, electrochemical methods, and especially covalently attached redox markers, attain an increasing interest. However, one problem is that the number of suppliers of electrochemically labelled oligonucleotides is very limited. This paper reports about the use of the commercially available fluorescence quenching label dabcyl (p-methyl red) as a redox active DNA-marker. We investigated the polarographic, voltammetric and adsorptive stripping voltammetric behaviour of this compound in a TRIS buffer at pH 7.5 and found that two polarographic waves (at −0.48 and −1.28 V vs. Ag/AgCl) can be easily distinguished compared to only one clear signal between −0.4 and −0.7 V in most voltammetric techniques.The alternating-current voltammetric (ACV) signal of a dabcyl-labelled target at a thiollinker-probe-SAM modified gold disk electrode was very clear but small due to a fast and irreversible decay of the reduction product. Despite of this, non-complementary DNA-strands could be discriminated and at 15 min hybridization time, trace amounts down to 50 nM target concentration could be detected. Such electrochemical use of optically active labels could open new possibilities for spectroelectrochemical studies of DNA hybridization. Keywords: DNA hybridization, Gold electrode, Voltammetry, Dabcyl, Methyl red, Self-assembled monolayer

Changes in the levels and spatial distribution of PAHs as a consequence of the Oder flood in the summer of 1997 were investigated in post-flood sediments from the Oder River and the Oder Lagoon. The aim of this study was to identify sources of the PAH pollution and in particular investigate polluted sites (“hot spots”) in the most highly suspected locations of the drainage area. Molecular indices based on isomeric PAH ratios and the ratio of the parent PAHs to methylated PAHs were used to distinguish between the pollution sources. Elevated levels of PAHs were discovered in the post-flood sediments of the Oder River in comparison to the average regional values. Elevated concentrations of PAHs were also found in fluffy layer samples taken from the Oder Lagoon and the Pomeranian Bight in late August. The highest concentrations of PAHs were observed near power plants or roads with heavy traffic. Most of the contamination originates from high temperature pyrogenic sources with some slight overlays of petrogenic sources. These increased concentrations of pyrogenic origin may be attributable to flooding of municipal and industrial waste disposal areas in the Oder River drainage. Die Auswirkungen der Oderflut 1997 auf die Verteilung von Polycyclischen Aromatischen Kohlenwasserstoffen in der Oder Als Folge der Oderflut im Sommer 1997 kam es in der Oder sowie im Oderhaff zur Erhohung der Belastungssituation sowie zu Anderungen der raumlichen Verteilung von polycyclischen aromatischen Kohlenwasserstoffen (PAK). Die Untersuchungen wurden an Nachflutsedimenten durchgefuhrt. Ziel dieser Studie war es, die Quellen der PAK-Kontamination zu identifizieren und in den zu erwartenden Hauptbelastungsgebieten die “hot spots” zu identifizieren. Mit Hilfe der Isomerenverhaltnisse verschiedener PAK zueinander und dem Verhaltnis der Eltern-PAK zu deren methylierten Homologen konnte zwischen den moglichen Kontaminationsquellen unterschieden werden. Im Vergleich zur Normalsituation konnten stark erhohte PAK-Konzentrationen in den Nachflutsedimenten der Oder gemessen werden. Eine erhohte Belastungssituation wurde ebenfalls im Fluffy-layer-Material des Oderhaffs und der Oderbucht Ende August 1997 identifiziert. Die hochsten PAK-Konzentrationen konnten im Einzugsgebiet groser Kraftwerke sowie in der Nahe von stark befahrenen Strasen gemessen werden. Hauptquellen der meisten Kontaminationen waren hochtemperaturpyrolytische Prozesse. Die petrogene PAK-Belastung wurde stark durch die pyrogenen Belastungsquellen uberlagert. Der Anstieg der pyrogenen PAK-Belastung ist vorwiegend auf die Uberflutung von stadtischen Mulldeponien und industriellen Mullhalden zuruckzufuhren.

The bismuth electrode exhibits similar electrochemical properties as most commonly used toxic mercury electrode and represents a suitable, reliable and also environmentally friendly tool for the detection of electroactive compounds at negative potentials. A wide operational potential window of the bismuth electrode from −200 mV to −1400 mV (vs. SCE) was found. Bismuth bulk electrodes (BiBE) are very convenient for sensitive adsorptive stripping voltammetric (AdSV) determination of the drug daunomycin in the nmol/L concentration range. In comparison with gold electrodes, the voltammetric signals of daunomycin at the bismuth electrode are higher and very well shaped. An accumulation potential of −0.65 V (vs. SCE) and accumulation time from 2 to 10 min were found to be optimal conditions for the preconcentration of daunomycin on the bismuth electrode surface. The adsorptive stripping response is linear over 100–1000 nmol/L concentration range (for 2 min deposition) and over 10–100 nmol/L concentration range (for 5 min deposition) with a detection limit of 5 nmol/L (for 8 min deposition). Repeatability was characterized by relative standard deviation 7.1% (for 10 measurements). The electrode must be regenerated between two consecutive measurements by polishing on a damp paper or by stirring in 96% ethanol for 5 min.

The technique of electrically heated carbon paste electrodes is applied for label-free detection of DNA hybridization after magnetic isolation. Coupling of both techniques leads to highly selective and sensitive detection of DNA hybridization. Minimal contributions of nonhybridized DNA are thus coupled to an enhanced signal. Application of elevated temperatures during the accumulation step yields a max. 6-fold enhancement of guanine oxidation signals compared to room temperature deposition. Use of noncomplementary nucleic acids gives no significant peaks at room or elevated temperatures. The noise level remained unaffected. Variation of the target concentration results in linear calibration plots under hot accumulation conditions.

Heated electrodes were applied for the non-isothermal operation of amperometric glucose biosensors based on glucose oxidase immobilised on the electrode surface by entrapment within a polymer layer. The localised deposition of the polymer film under simultaneous entrapment of the enzyme was achieved by an electrochemically induced pH-modulation in the diffusion zone in front of the electrode, thus altering the solubility of the polymer chains. This non-manual sensor preparation protocol could be successfully used for the modification of a novel indirectly heated electrode. The non-isothermal operating mode allows working at the optimum temperature of the enzyme sensors without any thermal distortion of the bulk solution. Increased surface temperature of the sensor thus accelerates transport as well as kinetic processes, resulting in an enhanced amperometric signal. In the presence of interfering compounds such as ascorbic acid, the proposed technique allows use of the diverging thermal impact on the sensing process, for different electrochemically active compounds, for a deconvolution of the amperometric signal at different electrode temperatures. A calculation method for determination of glucose in the presence of one interfering compound is presented as a basis for a calculative interference elimination.

Mercaptoundecanoic acid (MUA) and glutathione (GSH) self-assembled monolayers were prepared on gold- wire microelectrode. Cyclic voltammetry was used to investigate the influence of temperature on electrochemical behaviors of Fe(CN)63−/4− and Ru(NH3)63+/2+ at these SAMs modified electrodes in aqueous solution. It is found that temperature shows great influence on electron transfer (ET) and mass transport (MT) for the two SAMs modified electrodes and the influence of temperature depends on the charge properties of the redox couples and terminal groups of SAMs and the structure of the monolayer on gold surface. The temperature can greatly increase MT rate of Fe(CN)63−/4− at both MUA and GSH modified electrodes. However, the increased MT rate doesn't have any effect on the CV's for Fe(CN)63−/4− /MUA system. For Ru(NH3)63+/2+ , temperature can greatly improve the electrochemical reaction in both MUA and GSH modified electrodes, which is ascribed to temperature-induced diffusion and convection and the electrostatic interaction between Ru(NH3)63+/2+ and negatively charged carboxyl groups on the electrode surface.

Calf thymus DNA was modified on an electrically heated gold-wire microelectrode. Cyclic voltammetry was used to study the temperature behavior of Co(phen) 3 3+/2+ at a bare gold electrode and a DNA modified gold microelectrode at different electrode temperatures. It is found that the temperature has a great influence on the interaction between Co(phen) 3 3+/2+ and DNA. An increase of the peak current, a decrease of peak potential separation and a shift of the formal potential at a DNA modified gold electrode were observed with increase of the electrode temperature. This indicates that an increase in the electrode temperature cannot only improve the mass transfer, but also affect the nature of Co(phen) 3 3+/2+ binding to DNA.

Highly conductive boron-doped diamond (BDD) electrodes are well suited for performing electrochemical measurements of nucleic acids in aqueous solution under diffusion-only control. The advantageous properties of this electrodic material in this context include reproducibility and the small background currents observed at very positive potentials, along with its robustness under extreme conditions so offering promising capabilities in future applications involving thermal heating or ultrasonic treatment. tRNA, single and double stranded DNA and 2'-deoxyguanosine 5'-monophosphate (dGMP) have been studied and well defined peaks were observed in all cases, directly assignable to the electro-oxidation of deoxyguanosine monophosphate.

The results of a digital simulation for the determination of electrode temperature and near-electrode temperature gradients at a thin wire microelectrode heated by very short heating pulses are presented. The calculation results for temperature and temperature gradients, both as a function of time, are presented and discussed in comparison with experimental results. Fundamental limits and experimentally determined limits of maximum superheating up to temperature values far above boiling point at 1.0125 bar are demonstrated.

The behaviour of an electrically heated carbon paste electrode (CPE) with the surface modified by a calf thymus double stranded (ds) DNA adsorption layer was investigated in the medium of a copper(II) complex with 1,10-phenanthroline (phen) as the chemical nuclease. Damage to DNA is affected strongly by the electrode temperature within the range of 22–38°C as indicated by the square-wave voltammetric signals of the DNA redox marker Co(phen)33+ as well as the DNA guanine moiety. No significant effect of temperature on the binding constant was found at the titration of Cu(phen)22+ with dsDNA in solution. Thus, the formation of radical species and irreversible DNA damage are affected by DNA/CPE heating. The heated electrode can be applied advantageously to the real-time detection of traces of DNA-damaging agents.

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.

Hot-wire electrochemistry has been combined with stripping chronopotentiometry. The new hot-wire stripping potentiometric protocol couples the effective heat-induced metal deposition inherent to heated electrodes with the powerful stripping and sophisticated background correction of microprocessor-controlled chronopotentiometry. Such coupling is demonstrated in connection to trace measurements of mercury at a gold wire microelectrode. The greatly enhanced mercury signal accrued from the use of the heated electrode obviates the need for a forced-convective hydrodynamic systems (as desired, for example, in remote/submersible stripping operations). Using an electrode temperature of 60°C and a quiescent solution, the response is linear over the 0.5–25 μg/l range tested (2 min deposition), with a detection limit of 80 ng/l (following a 10 min accumulation).

The technologic basis for in situ heating of a microelectrode wire by high amplitude, high frequency alternating current (hot-wire electrochemistry) is presented. The preferred modes are continuous heating until a stationary temperature value is established, and pulsed heating with short time current sampling. The latter allows measurement above the boiling point.

An improved electrode design to perform electroanalytical measurements in organic solutions at elevated temperatures was constructed. In this method, a thin platinum wire is directly heated by ac current and an electrochemical signal at this wire is measured simultaneously. The electrode temperature in THF was determined by investigating the open circuit potential of the redox couple ferrocene|ferrocenium. The heating effects are demonstrated by cyclovoltammetric measurements of ferrocene at different scan rates and temperatures. The observed mass transport limiting current values strongly depend on the temperature. The quality of the measurements was examined using an Arrhenius plot. Keywords: Hot wire electrochemistry, Ac heating, Cyclic voltammetry, Cylindrical microelectrodes, Ferrocene, Tetrahydrofuran

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.

The oxidation of formaldehyde, methanol, formic acid and glucose on Pt was studied at increased temperatures under non-isothermal conditions by cyclic voltammetry. The platinum electrode (25 μ m diameter wire) was heated continuously with a high frequency ac (100 kHz) during dc polarization (see also Ref. [T. Zerihun, P. Grundler, J. Electroanal. Chem., 404 (1996) 243.] ). The heating power employed determines the temperature attained at the electrode surface (up to ca. 79°C in the present experiments). The catalytic activity of the platinum electrode (99.9% Pt) without ac heating was observed to be particularly low. On the other hand, markedly increased oxidation current signals of the organic substances were obtained at a heated electrode. Apparently, the self-poisoning effect of platinum, which is common in the oxidation of small organic molecules and glucose, decreases with increasing reaction temperature. The overall oxidation reaction will thus be enhanced at raised temperatures. The oxidation reactions of the small organic molecules also occur at increasingly lower potentials with increasing temperatures. This may be due to the decrease of the overvoltage for the formation of adsorbed OH (a reactive species involved in the oxidation of the organic substances) on Pt. Additional experiments performed in thermostated systems are also presented for the purposes of comparison.

The experiment involved cathodic stripping analysis of electrodeposited PbO 2 in aqueous solutions of Pb 2+ and HClO 4 on a vertically arranged cylindrical Pt microelectrode (25 μm diameter) at increased electrode temperature and free convection. The electrode was continuously heated in-situ using a 100 kHz alternating current during d.c. polarization. The stripping signals at the heated electrode were much better than those obtained at room temperature. Cyclic voltammetry and potentiostatic (anodic) deposition followed by a negative linear potential sweep were used for the deposition and stripping of PbO 2 .

In the present paper heat transfer in a fluid is considered. The Oberbeck-Boussinesq equations for stream function and vorticity are solved by a finite difference method. In the presence of very strong convection pulse type solutions occur. The results are applied in the design of microsensors and compared with experimental data.

A platinum microelectrode (25 μm diameter cylinder) heated by alternating current was used to study the reduction of oxygen in neutral phosphate buffer solution using cyclic voltammetry. Interference of the a.c. voltage on the electrode process was completely avoided when high frequency a.c. (100 kHz) was used. The electrode temperature was determined indirectly from the changes in open circuit potentials in a hexacyanoferrate(II)/(III) system. The influence of electrode orientation on the contribution of convection to mass transfer was shown by considering horizontally and vertically positioned electrodes. A linear relationship between the reduction currents and the oxygen concentrations was obtained. In all cases the oxygen reduction signals were improved upon heating.

Heated wires in a special symmetrical arrangement were used for electrochemical experiments in a thin, hot, near-electrode solution layer. By application of a series of short-time heat pulsing sequences with current sampling and synchronized polarization steps, voltammetric curves above the boiling point were recorded. Methods for determining and controlling the actual temperature are presented. The temperature dependence of quantities such as diffusion coefficient or electrode potential can be determined in a convenient manner. Examples are given for different redox systems, including hexacyanoferrate(III)–(II), Fe3+–Fe2+, bromate, oxalic acid and formaldehyde.

An improved electrode design enabled to perform electroanalytical experiments in which a platinum wire electrode inside an aqueous electrolyte solution was continuously joule heated during dc polarization. The proposed symmetrical electrode arrangement allowed measurement of low magnitude electrochemical signals even when a high magnitude audio frequency current was used for heating. The new arrangement could open a way to amperometric sensing of sluggish reacting species without changing bulk solution temperature. The electrochemical behaviour of a platinum wire surface exposed to these conditions was considered. The heating effects are demonstrated by cyclic voltammograms of hexacyanoferrate(II)/(III) and by cathodic stripping of dissolved oxygen at the hot platinum surface.

A galvanic cell for trace determination of hydrogen sulfide in gases is presented. The cell covers the range from 30 ppb to some hundred ppm. It is characterized by simple construction. The use of ferricyanide/ferrocyanide ions as a redox mediator system ensures very low cross sensitivity. The sensor is well-suited for mobile use.

Als die Nachrichten 1953 zum ersten Mal erscheinen, ist die Polarographie die modernste elektrochemische Analysenmethode. Heute nutzt man elektrochemische Prinzipien in Biosensoren, in der DNA-Diagnostik und in „Lab-on-chip”-Anwendungen.

A simple galvanic cell without any external voltage for the trace determination of hydrogen sulphide is described. The signal corresponds to the concentration of the dissolved molecular H2S. For the calculation of total sulphide, the pH has to be taken into consideration. The sensor was tested in the range of concentration from 3·10−6 mol/l H2S to 9·10−5 mol/l H2S for pH