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It has been investigated how increased temperatures affect the deposition and stripping step during stripping analysis of Cu(II), Hg(II) and As(III). Results obtained at a heated gold wire have been compared to those obtained at a rotating gold disk electrode. The sensitivity has been found to be higher at the hot-wire electrode. The signal-to-noise ratio was also better at the heated gold wire. The lowest Cu(II) concentration detectable was 10−9 mol/L at the heated gold wire compared to 10−7 mol/L at the rotating disk. Comparing the results and executing a protocol consisting of three consecutive scans after one single deposition w/o heat with all three elements showed a quite different behavior. Best signals have been obtained if only conditioning and deposition are done at increased temperature. Deposit is also removed more efficiently during the first scan in this case. Reasons for this are discussed.

This article introduces a new heated mercury film electrode based on a screen-printed carbon substrate. The sensor is easy-to-build and the material costs compared to its iridium-based counterpart are low. The development procedure including electrode construction, mercury deposition and thermal properties is described in detail. As first application, cadmium and lead were determined by square-wave anodic stripping voltammetry with significantly improved signal-to-noise characteristics.

Das Frequenzhammerchen erlaubt einen preiswerten Einstieg in die frequenzielle Diagnostik: jede gewunschte Informationsebene ist durch die Einstellung einer vorprogrammierten oder frei programmierbaren Frequenz rasch zuganglich und die Patienten werden durch das elektrische Feld gleichzeitig so stabilisiert, dass auch bei storenden Frequenzen keine Oszillation auftritt.

Hot-wired electrodes: Thin metallic wires (d=25 μm) are covered with a 3 μm layer of single-walled carbon nanotubes (SWCNTs; see image) by electrophoresis from a suspension containing excess ionic surfactant. A pure SWCNT surface is achieved by heating the electrode in air. Strong differences between covered and bare metallic electrodes occur with in situ heating during electrochemical experiments. The use and preparation of single-walled carbon nanotubes (SWCNTs) at thin metallic wire electrodes for hot-wire electrochemical studies is described. The nanotubes were deposited on metal substrates such as gold by electrophoresis from a dispersion containing sodium dodecyl sulphate as an anionic surfactant. The formation of a layer of pure SWCNTs is achieved by thermal treatment at 350 °C. When heated in situ by a strong ac current, the electrodes can be used for electrochemical studies of nanotubes at increased temperatures. The state and functionality of the electrodes were characterized by Raman spectroscopy, scanning electron microscopy, and cyclic voltammetry with both anionic and cationic redox systems (dopamine, ferrocene carboxylic acid). First time experiments at the heated SWCNT electrodes demonstrated an excellent suitability of these as-prepared electrodes for thermoelectrochemical studies.

A directly heated mercury film electrode (MFE) extends the operational capabilities of the hot layer technique to a wide range of electroanalytical systems. Wires or layers of gold and platinum have been used as sensors so far, but they were suitable only for the analysis of a small number of metals. The development of a heated MFE is described, including electrode construction and mercury deposition procedures. The thermal properties of the sensor were investigated. As a first application, cadmium was determined by anodic stripping voltammetry (ASV) with the result of an improved signal-to-background ratio. Keywords: Mercury film electrodes, Heated electrodes, Iridium, Anodic stripping voltammetry, Cadmium

Voltammetry with continuously heated microelectrodes yields well-defined sigmoidal current-voltage curves. Unlike hydrodynamic electrodes, the surface temperature of a heated electrode can be adjusted arbitrarily within a certain range. Inside a thermal layer, a virtually stagnant diffusion layer of constant thickness δ diff exists. δ diff is independent of temperature within a certain range. On the basis of this theory, equations are derived which play a similar role to, for instance, the Levich equation for the rotating disk electrode. Reasonable agreement of the derived relationship with the results from voltammetric experiments is obtained.

The electrodeposition of lead on boron-doped diamond has been studied with a view to identifying the fundamental parameters controlling the sensitivity and lower detection limit in anodic stripping voltammetry. Chronoamperometric transients are used to explore the deposition, indicating a progressive growth mechanism confirmed by ex situ AFM images. Linear sweep ASV experiments show a threshold concentration of ca 10−6 M below which no lead is detected; this is attributed to the need for nucleation of the solid phase on the electrode. Experiments with variable temperature show that this threshold can be usefully lowered at elevated temperatures.

A new electrically heated carbon paste electrode has been developed for performing adsorptive stripping measurements of trace nucleic acids. Such coupling of electrochemistry at electrically heated electrodes with adsorptive constant-current stripping chronopotentiometry offers distinct advantages for trace measurements of nucleic acids. The application of increased temperatures during the deposition step results in dramatic (4-34-fold, depending on temperature applied) enhancement of the stripping signal. Such improvement is attributed to the accumulation step at the heated electrode. Forced thermal convection near the electrode surface facilitates the use of quiescent solutions and hence of ultrasmall volumes. Using an electrode temperature of 32 degrees C and a quiescent solution during the 1-min accumulation, the response is linear over the 1-8 mg/L range tested, with a detection limit of 0.5 mg/L. Such electrode heating technology offers great promise for various applications involving thermal manipulations of nucleic acids.

Microelectrode wires heated directly in situ by an electric current generate mass as well as heat energy transport phenomena. With continuous heating, a stationary surface temperature is established as a result of thermally promoted convection. The geometry of concentration and temperature profiles under these conditions are investigated by cyclic voltammetry, potential step experiments, and finite element simulation of convection and diffusion processes. It is shown that the Nernst diffusion layer approaches a constant, temperature-independent thickness if the temperature difference between bulk and electrode surface exceeds ca. 30 K in aqueous solution. At continuously heated wire electrodes, diffusion coefficient values as well as kinetic data can be determined under well-defined temperature conditions, and in a very convenient way.

This paper describes the design of a hot-wire electrochemical flow detector, and the advantages accrued from the effects of locally increased temperature, mainly thermally induced convection, upon the amperometric monitoring of flowing streams. A new hydrodynamic modulation voltammetric approach is presented, in which the solution flow rate remains constant while the temperature of the working electrode is modulated. Factors influencing the response, including the flow rate, temperature pulse, or applied potential, have been investigated. The hot-wire operation results also in a significant enhancement of the flow injection amperometric response. The minimal flow rate dependence observed with the heated electrode should benefit the on-line monitoring of streams with fluctuated natural convection, as well as various in-situ remote sensing applications.

Die Aufklarung von Art und Menge der in chemischen Verbindungen oder Stoffsystemen vorkommenden Elemente ist von grundlegender Bedeutung fur die Entwicklung von Naturwissenschaft und Technik. Aus den gewonnenen Informationen werden beim Vorliegen definiert zusammengesetzter Verbindungen unter den jeweils geltenden thermodynamischen Bedingungen konkrete Formelangaben abgeleitet. Diese geben zuverlassig Auskunft uber die Stochiometrie der Systeme und Aufschlus uber die Wertigkeit der am Aufbau der chemischen Verbindungen beteiligten Elemente. So folgt z. B. aus der Formel ZnO fur Zinkoxid die eindeutige Aussage, das die Elemente Zink und Sauerstoff in ihren zweiwertigen Wertigkeitszustanden im angegebenen Atomverhaltnis vorliegen. Solche klaren Aussagen sind jedoch aus analytischen Befunden nicht mehr abzuleiten, wenn die zu bewertenden Stoffsysteme durch Verunreinigungen oder das Vorkommen von Elementen in unterschiedlichen Wertigkeitszustanden von komplizierter Art sind. In diesen Fallen wird die Ermittlung der Stochiometrie der in Stoffsystemen vorliegenden Verbindungen allein aus der Bestimmung der Art und Menge der im System vorkommenden Elemente praktisch unmoglich. Das Heranziehen zusatzlicher Informationen uber die Art und Menge der Verunreinigungen und zur Phasenzusammensetzung wird zur unabdingbaren Voraussetzung, um uberhaupt zur Stochiometrie einzelner chemischer Verbindungen Aussagen gewinnen zu konnen.

Bismuth-coated carbon paste electrodes display an attractive stripping voltammetric behavior which improves greatly upon heating the electrode during the deposition step. Such “hot-electrode” operation leads to a dramatic enhancement of the stripping peaks of lead, cadmium and zinc, while retaining low background currents. The influence of relevant parameters, including the heating current, deposition potential and deposition time is examined. The stripping signals for selected heavy metals result in sharp, well defined and undistorted peaks, with favorable reproducibility (5%). Highly linear calibration plot (correlation coefficient, 0.9986) is observed over the 20–140 μg/L lead range. An estimated detection limit of 3.16 μg/L lead could be observed on the basis of signal-to-noise ratio.

Zusammenfassung Nach der Methode der Reaktionsstufen-Coulometrie wurden Gemische von Cer(IV) und Chlorat bzw. Hypochlorit und Chlorat analysiert durch Titration mit coulometrisch an einer Quecksilberkathode in saurer, chloridhaltiger Losung erzeugtem Titan(III). Die Konzentrations-Zeit-Kurven wurden amperon etrisch bzw. biamperometrisch verfolgt. Die Reduktionsgeschwindigkeit des Chlorats wurde durch Anwendung des primaren Salzeffekts modifiziert. Um Chlorverlust bei der Titration des Hypochlorits zu vermeiden, wird eine geschlossene Elektrolysezelle vorgeschlagen.

Zusammenfassung Unterschiedliche kinetische Eigenschaften zweier Substanzen in Losung werden ausgenutzt um beide Substanzen mit einem coulometrisch erzeugten Titrationsmittel separat zu titrieren. Die zwei Konzentrationen lassen sich aus den wahrend der Titration auftretenden Konzentrations-Zeit-Kurven ablesen. Fur zwei oxydierende Stoffe werden die entstehenden Konzentration-Zeit-Kurven theoretisch abgeleitet. Fur die analytische Anwendung mussen die Reaktionsgeschwindigkeitskonstanten bestimmte Bedingungen einhalten. Der Einflus der amperometrischen Indikation auf die Form der experimentell mesbaren Kurven wird diskutiert.

Hypochlorite was determined by direct coulometric titration with iron(II) in an acetate buffered solution. Chlorate was titrated with titanium(III) in 2M hydrochloric acid. Amperometric indication with one and two electrodes, respectively, was used. Mixtures of hypochlorites and chlorates, e.g., in industrial electrolytes, may be analysed. On a determine l'hypochlorite par titrage coulometrique direct avec le fer(II) dans une solution tamponnee a l'acetate. On a titre le chlorate avec le titane(III) en acide chlorhydrique 2M. On a utilise l'indication amperometrique une et deux electrodes respectivement. On peut analyser des melanges d'hypochlorites et de chlorates, par exemple dans des electrolytes industriels.

Hot-wire electrochemistry can be a valuable aid in stripping analysis at solid electrodes. Deposition as well as stripping can be done with increased temperature at remote places, leaving the bulk solution unaffected. As an example, arsenic(V) traces were deposited directly without prior reduction at a heated 25 μm gold electrode. Deposition was followed by anodic stripping. Presence of gold(III) ions had a positive effect. The detection limit was enhanced by a factor of 14 when going from 22°C to 60°C. The effects are explained by assuming that inhibited chemical reactions are activated and that transport processes inside and outside the electrode are accelerated.

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. Keywords: Hot-layer electrochemistry, Temperature pulse voltammetry, Differential pulse voltammetry, Low-temperature cofired ceramics, Heated electrodes, Redox entropy

In hot‐wire electrochemistry electrode wires are heated in situ by electric current with a uniform temperature along the length being desirable. Using IR photography and digital simulation the degree of nonuniformity of the temperature along the wire was estimated. A strong influence of the thermal conductivity of the surrounding media was found. Furthermore it is shown that heated microelectrode wires have a uniform temperature over nearly their entire length. © 2000 The Electrochemical Society. All rights reserved.