Name: dynamic electrochemical measurement of chloride ions
Uploaded: 2016-02-05T13:00:00.000+00:00
Duration: 7 min 32 s
Description: Watch this Scientific Journal Video about Dynamic Electrochemical Measurement of Chloride Ions at JoVE.com

This work is a part of the STW project "Integral solution for sustainable construction (IS2C, Fleur van Rossem for her support during the chip fabrication, Justyna Wiedemair for the chip design and Allison Bidulock for her support during the manuscript preparation.

1. Chipfertigungs Hinweis: Der Chip besteht aus einer Ag / AgCl-Arbeitselektrode (WE), eine Ag / AgCl Pseudo-Referenzelektrode (Pseudo-RE) und einer Platin-Gegenelektrode auf einem Glas-Chip. Die Silbermetall auf einem Glas-Chip abgelegt, Standard Reinraum mit verarbeitet 16. Es wird dann in 0,1 M FeCl &amp; sub3; -Lösung für 30 sec chloriert eine AgCl-Schicht über der Oberfläche zu bilden. Die Ag / AgCl WE (Bereich = 9,812 mm 2) ist in der Mitte, umgeben von der Ag / AgCl Pseudo-RE wie in Abbildung 1 dargestellt. <ol><li> Zahlen Sie das Silbermetall auf Glas eine ebene Silberelektrode zu bilden. Der Schritt-für-Schritt-Chipherstellung in einem Reinraum ist wie folgt gegeben: <ol><li> Lithografie <ol><li> Für Waferreinigung, tauchen die Glasscheibe zunächst in konz. HNO 3 Bad jede organische Verunreinigungen zu entfernen und dann in 1 M KOH die Oberfläche zu reinigen. </li><li> Tragen Sie eine positive Fotolack (200 nm dick) auf dieWafer durch Schleuderbeschichtung und Vorbacken die für 15 min bei 95 ° C widerstehen. </li><li> Expose des Wafers mit UV-Licht für 5 Sekunden durch eine Glasmaske. </li><li> Entwickeln des Photoresist in Entwicklerlösung. Dadurch wird die Glasfläche freizulegen, wo Elektroden abgelagert wird und die restliche Fläche wird von der unbelichtete Resist abgedeckt werden. </li></ol></li><li> Glass Etching <ol><li> Tauchen des entwickelten Glaswafer in dem KOH-Bad die belichtete Fläche des Glases zu ätzen. </li></ol></li><li> Metal Deposition (Sputtering) <ol><li> Kaution Silbermetall auf der freiliegenden Glasfläche. <ol><li> Erste Einzahlung eine 20 nm Titan (Ti) Schicht (durch Sputtern) als Haftschicht für Glas. </li><li> Dann abzuscheiden 70 nm Palladium (Pd) -Schicht (durch Sputtern) als Diffusionsbarriere zwischen Silber und Ti. </li><li> deponieren Schließlich 500 nm aus Silbermetall. Dies ist die Dicke des abgeschiedenen Metalls. Die Fläche der Arbeitselektrode beträgt 4 mm 2. </li><li> Entfernen Sie die remaining mit dem Lift-off-Prozess in einer Aceton-Bad widerstehen. </li></ol></li><li> Würfeln Wafer in die Single-Chip-Größe. Der Chip ist nun bereit, chloriert werden, um eine On-Chip-Ag / AgCl-Elektrode zu bilden. </li></ol></li></ol></li><li> Platzieren Sie den Chip in einer in-house entwickelt Polytetrafluorethylen Chiphalter, wie in Abbildung 1 dargestellt. Die Halterung ermöglicht eine einfache elektrische Verbindungen via Push-Pins (oder Federstifte) und enthält eine elektrochemische Zelle. </li><li> Chloridize die Silberelektrode eine Ag / AgCl-Elektrode auf dem Chip zu bilden. Dafür gießen 0,1 M FeCl &amp; sub3; -Lösung in die Zelle für 30 sec. oder bis die silberne Farbe der Elektrode wird dunkel grau. Längere Eintauchen ist nicht entscheidend, wohingegen kürzere Tauchzeit zu keiner Abscheidung von Ag / AgCl führen kann. </li><li> Den Chip mit VE-Wasser spülen restlichen FeCl 3 .Die Chip zu reinigen ist nun bereit für die chronopotentiometrischen Messung verwendet werden. </li></ol>2. Vorbereitung Electrolyte Anmerkung: Die Elektrolyte wurden mit verschiedenen Konzentration an Kaliumchlorid in 0,5 M KNO 3. <ol><li> Vorbereitung 50 ml 50 mM KCl-Elektrolyt-Stammlösung (0,186 g KCl in 50 ml Lösung). </li><li> In der gleichen Lösung, 2,52 g KNO 3 hinzufügen einer 0,5 M KNO 3 Hintergrundelektrolyten zu bilden. </li><li> Halten Sie die Ausgangskonzentration an Chlorid auf Null und KNO 3 bis 0,5 M. In anderen Worten fügen 2,52 g KNO 3 in einem 50 ml entionisiertem Wasser. </li><li> Zugeben von 50 mM KCl die Chloridionenkonzentration (von 1 mM bis 6 mM) des Elektrolyten zu erhöhen, systematisch, wie in den folgenden Schritten gezeigt ist. <ol><li> 100 l des 50 mM KCl in 4,9 ml 0,5 M KNO 3 1 mM [cl] zu erhalten. </li><li> Hinzufügen 104 ul der 50 mM KCl-Lösung in die Lösung aus Schritt 2.4.1 2 mM [Cl] zu erhalten. </li><li> In 108.41 ul der 50 mM KCl-Lösung in die solution von Schritt 2.4.2 3 mM [cl] zu erhalten. </li><li> Hinzufügen 113.19 &amp; mgr; l des 50 mM KCl-Lösung in die Lösung aus Schritt 2.4.3 4 mM [Cl] zu erhalten. </li><li> Hinzufügen 118,2 &amp; mgr; l des 50 mM KCl-Lösung in die Lösung aus Schritt 2.4.4 5 mM [Cl] zu erhalten. </li><li> Hinzufügen 123,3 &amp; mgr; l des 50 mM KCl-Lösung in die Lösung aus Schritt 2.4.5 6 mM [Cl] zu erhalten. </li></ol></li></ol> 3. Versuchsaufbau Anmerkung: Die Messungen wurden durchgeführt unter Verwendung eines Potentiostaten (Biologic Wissenschaft Instruments, Frankreich). <ol><li> Platzieren Sie den Chip in der Chiphalter und verbinden Sie den entsprechenden Anschluss des Potentiostaten. </li><li> Schließen Sie den Arbeitselektrodenanschluss des Potentiostaten auf die Ag / AgCl-Elektrode. </li><li> Verbinden der Referenzelektrodenanschluss des Potentiostaten auf einen anderen Ag / AgCl-Elektrode. </li><li> Verbinden der Gegenelektrodenanschluss des Potentiostaten auf der Platinelektrode. </li><li> Setzen Sie den complete Versuchsaufbau in einem Faradayschen Käfig Umgebungsgeräusche zu vermeiden. </li></ol> 4. Instrument Betriebseinstellungen Anmerkung: Die Betriebsparameter der elektrochemischen Zelle werden über die Benutzerschnittstelle des Potentiostaten kontrolliert. Die Potentialantwort des Ag / AgCl WE während einer angelegten Stromimpuls ist für verschiedene Konzentrationen an Chloridionen gemessen. <ol><li> In den Potentiostaten Programm, öffnen Sie die Technik Chronopotentiometrie und legen Sie die Betriebsparameter. <ol><li> Stellen Sie die folgenden Parameter entsprechend den Anforderungen: <ol><li> Strom (I s) </li><li> Zeit angelegten Strom (t s) </li></ol></li><li> Starten Sie diese Technik durch die Play-Taste in den Potentiostaten Programm klicken. Hinweis: Der Potentiostat Programm zeigt die Potentialantwort als Funktion der Zeit unter der Stromimpuls angelegt. </li></ol></li></ol> 5. Messungen und die Anas <ol><li> Zeichnen der Kalibrierungskurve des Übergangszeit vs. Cl-Ionenkonzentration im Elektrolyten. <ol><li> Ändern Sie den CL-Konzentration im Elektrolyt KCl, systematisch. <ol><li> Starten Sie die Messung mit 5 ml 1 mM KCl mit 0,5 M KNO 3 Hintergrund Elektrolyt in der elektrochemischen Zelle. </li><li> Starten Sie die chronopotentiometrischen Experiment des Potentiostaten verwendet und einen Strom von 10 mA / cm -2 für 10 sec anzuwenden und die Daten speichern. </li><li> ändern systematisch die Konzentration bis 6 mm mit 1 mm-Schritten und die Messungen wiederholen. </li></ol></li><li> Lagern Sie die Messdaten als a.mpt Datei und analysieren in Datenverarbeitungsprogramm die Datendatei. <ol><li> Analysieren Sie die Daten, die eine selbst entwickelte Datenverarbeitungsprogramm unter Verwendung der ersten Ableitung des Potentials Antwort zu berechnen und den Höhepunkt der ersten Ableitung berechnen. Der Peak der ersten Ableitung ist die Übergangszeit. Hinweis: Der komplette KabeljauIng Datenverarbeitungsprogramm wird in der Zusatzinformation von Abbas gegeben et al. 2014. </li></ol></li><li> Wiederholen Sie die Messung dreimal mit dem Intervall von 1 Stunde je. </li><li> Öffnen alle Datendateien in Datenverarbeitungsprogramm und berechnen die Übergangszeit für jede Messung. Detail Schritte von Übergangszeit Berechnung ist unten angegeben: <ol><li> Zeichnen Sie die Potentialdifferenz als Funktion der Zeit von den Datendateien von chronopotentiometrischen Messung erhalten. </li><li> Berechnen der ersten Ableitung der Potentialantwort. </li><li> Zeigen das Maximum der ersten Ableitung und den Zeitpunkt davon. Der Zeitpunkt des Maximums der ersten Ableitung ist die Übergangszeit. </li></ol></li><li> Für die Eichkurve zeichnen Sie die Quadratwurzel aus der Übergangszeit in Bezug auf die Konzentration von Cl-Ionen. </li><li> An den Messdaten des Grundstückes der theoretischen Kurve auf der Grundlage der Sand Gleichung 25. Berechnen Sie die Diffusion zient zurückabler von der Datenaufzeichnung. <ol><li> In der Messdaten Grundstück zwischen Übergangszeit und die [cl], um jeden Punkt auf der Linie und notieren Sie den Wert der Übergangszeit und die [cl]. Der Sand Gleichung gegeben ist als: τ = (FC * / 2j (1-t Cl -)) 2 Dπ Hier, C * ist die Schütt Cl-Ionenkonzentration, F die Faraday-Konstante, j die Stromdichte, t Cl - ist die Überführungszahl und D der Diffusionskoeffizient. Die Vernachlässigung der TCL - da sie gegen Null für höhere Hintergrundelektrolytkonzentration. </li><li> Die einzige verbleibende Variable in der Gleichung Sand in dem Diffusionskoeffizienten; stellen den Wert der Übergangszeit, die Chloridionenkonzentration und dem angelegten Strom in den Sand Gleichung den Wert des Diffusionskoeffizienten zu bekommen. </li></ol></li></ol></li><li> Drift Mess <ol><li> Gießen 5 ml von 1 mM der KCl in derelektrochemischen Zelle. </li><li> In den Potentiostaten, setzen die angelegte Strom 10.00 -2 und Zeit zu sein, 10 sec. </li><li> Messen der Potentialantwort für 2 Wochen mit drei Mess jeden Tag mit einem Intervall von 3 Stunden zwischen den Messungen. </li><li> Aktualisieren des Elektrolyten, dh 1 mM KCl, jeden Tag, bevor die Messungen durchführen. </li><li> Zeichnen Sie die Übergangszeit mehr als zwei Wochen von Messungen. Die Änderung der Übergangszeit pro Tag ist die Drift des Übergangszeitverhalten. </li></ol></li><li> Wirkung der Pseudo-Referenzelektrode, die auf den Übergangszeitmessungen Hinweis: Verschiedene pseudo-Referenzen wie einer Ag / AgCl-Draht, einem Platindraht und einem Stahldraht werden getestet, um die Übergangszeit zu messen. <ol><li> Pour 4 mM KCl Elektrolyt in der elektrochemischen Zelle. </li><li> Verwenden Ag / AgCl als Pseudo-Referenzelektrode und verbinden es mit dem Referenzelektrodenanschluss des Potentiostaten. Durch die anodische Stromimpuls der Cl &amp; #713; Ionen werden in der Nähe der Ag / AgCl Arbeitselektrode aufgebraucht. </li><li> Führen Sie die chronopotentiometrischen Messung durch eine Stromdichte von 15 Am -2 für 10 sec aufgebracht wird. </li><li> Wiederholen der Messungen mit Platin als Pseudo-Referenzelektrode und die Daten aufzuzeichnen. </li><li> Wiederholen Sie die Messung mit Stahlstab als Pseudo-Referenzelektrode und die Daten aufzuzeichnen. </li><li> Zeichnen Sie die gemessenen Übergangszeit für verschiedene Pseudo-Referenzelektroden verwendet. </li><li> Wiederholen Sie den kompletten Satz der Messung mit 5 mM KCl und zeichnen die Übergangszeit verschiedene Pseudo-Referenzelektroden. </li></ol></li></ol>

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The authors have nothing to disclose.

Die Übergangszeit ist der Moment der Einbiegung; es ist theoretisch unabhängig von dem Bezugspotential dh der Referenzelektrode. Daher ist jede Metalldraht kann für Übergangszeitmessungen als Pseudo-Referenzelektrode benutzt werden. Im Gegensatz zu den bestehenden potentiometrischen Messung von Chloridionen in Beton ermöglicht dieses Verfahren eine langfristige und Kalibrierung freie Messung. Weiterhin ist die Empfindlichkeit und die Nachweiskonzentrationsbereich kann durch Einstellen der angelegten Stromi...

Eine Chloridionensensor auf der Basis des Übergangszeitmessung einer Ag / AgCl-Elektrode dargestellt. Das Ziel ist es, die inhärenten Driften während des langfristigen kontinuierlichen Überwachung der Chloridionen in dem Elektrolyten zu vermeiden. Chronopotentiometrischen Messung, die eine dynamische Messung Ansatz ist, einer Ag / AgCl-Elektrode ist zu diesem Zweck verwendet. Hier ist eine Änderungsrate des Potentials einer Ag / AgCl-Elektrode ist während eines Stimulus (galvanostatischen Impuls) gemessen. Der Vorteil dieses Ansatzes ist durch entzieht die Flüssigkeit-Übergang Referenzelektrode nachgewiesen und stattdessen unter Verwendung jeder Metalldraht als Pseudoreferenzelektrode, ermöglicht so den Nachweis von Cl-Ionen-Konzentration für langfristige (Jahre) und in situ-Anwendungen, wie beispielsweise Messung in Betonkonstruktionen. Chloridionen in Betonstrukturen ist eine der wichtigsten Ursachen der Verschlechterung 1,2. Es initiiert Lochfraß in der Bewehrungsstahl einnd Ergebnisse in der endgültigen Versagen der Struktur 3. Daher Ionen in Beton Cl Messung unvermeidlich die Lebensdauer und Wartungszyklus einer Struktur 4,5 vorherzusagen. Verschiedene Messprinzipien sind für Chloridionen Messung im Beton wie elektrochemische 6,7, optische 8,9 und elektromagnetische 10,11 ausgewiesen. Jedoch optische und elektromagnetische Methoden sperrige Aufbauten haben, sind schwierig als Stand-Alone-System zu integrieren und haben Probleme mit Selektivität 12. Bei elektrochemischen Technik, potentiometrischen Messung eines Ag / AgCl-Elektrode ist der Stand der Technik Ansatz 6,7,13. Trotz vielversprechender Ergebnisse ist dieser Ansatz zu Labormaßstab Messung, da die Antriebe in Bezug Potential und Diffusionsspannungsabfall führt zu fehlerhaften Daten 14,15 begrenzt. Eine Übergangszeit Ansatz basiert auf dem dynamischen elektrochemischen Messung (DEM) konnte das Problem wegen der möglichen lindernDrift 16. In dem DEM wird eine Systemantwort auf eine angelegte Stimulus gemessen 17-19. Das Beispiel eines solchen Systems ist Chronopotentiometrie. Hier ein angelegter Stromimpuls wird als Stimulus verwendet, um Ionen in der Nähe der Elektrodenoberfläche abbauende und das entsprechende Potenzial Reaktion gemessen wird. Ein anodischer Strom bei einer Ag / AgCl-Elektrode leitet einen Faradayschen Reaktion (Ag + Cl <img alt="Abbildung 1" src="/files/ftp_upload/53312/arrow.jpg" /> AgCl + E), was zu einer Verarmung von Cl-Ionen in der Nähe von Elektrodenoberfläche. Die Potentialänderung ist eine Funktion des angelegten Stroms und die Konzentration der (selektiven) -Ionen in der Elektrolyt 12,20. In dem Moment, diese Ionen verarmen vollständig in der Nähe der Elektrode schnell die Geschwindigkeit der Änderung des Potentials steigt die Oberfläche, was einen Wendepunkt 21. Der Wendepunkt auf dem Potential Zeitantwortkurve (chronopotentiogram) zeigt die Übergangszeit und kann von der bestimmt werdenMaximum der ersten Ableitung der Potentialantwort 22. Die Übergangszeit ist ein Merkmal der Ionenkonzentration. Dieser Ansatz ist verwendet worden 23,24 verschiedenen Ionen-Konzentration 17 und den pH-Wert von Elektrolyten zu bestimmen. Im Falle einer Ag / AgCl-Elektrode als Arbeitselektrode (zu dem Strom angelegt wird) die abbau Ionen Chloridionen 17 sein wird. Daher seine Übergangszeitmessung wird ihre Konzentration bestimmen.

<table><tbody><tr><td>Platinum wire (&amp;ge;99.99% trace metals)</td><td>Sigma Aldrich, the Netherlands</td><td>EP1330-1EA</td><td></td></tr><tr><td>Potassium chloride (BioXtra, &amp;ge;99.0%)</td><td>Sigma Aldrich, the Netherlands</td><td>P9333-500G</td><td></td></tr><tr><td>Potassium hydroxide (90% pure reagent grade)</td><td>Sigma Aldrich, the Netherlands</td><td>484016-1KG</td><td></td></tr><tr><td>Ferric chloride&amp;nbsp;</td><td>Sigma Aldrich, the Netherlands</td><td>451649-1G</td><td></td></tr><tr><td>potassium nitrate (&gt;99% reagent grade)&amp;nbsp;</td><td>Sigma Aldrich, the Netherlands</td><td>P6083-500G</td><td></td></tr><tr><td>Ag/AgCl liquid junction reference electrode&amp;nbsp;</td><td>BASi, USA</td><td>model MF-2079</td><td></td></tr><tr><td>VSP potentiostat</td><td>Biologic Science Instruments, France</td><td>VSP 300</td><td></td></tr><tr><td>Steel wire</td><td>Microlab TU Delft</td><td></td><td></td></tr><tr><td>Silver wire&amp;nbsp;</td><td>Sigma Aldrich, the Netherlands</td><td></td><td></td></tr></tbody></table>

dynamic electrochemical measurement of chloride ions

This protocol describes the dynamic measurement of chloride ions using the transition time of a silver silver chloride (Ag/AgCl) electrode. Silver silver chloride electrode is used extensively for potentiometric measurement of chloride ions concentration in electrolyte. In this measurement, long-term and continuous monitoring is limited due to the inherent drift and the requirement of a stable reference electrode. We utilized the chronopotentiometric approach to minimize drift and avoid the use of a conventional reference electrode. A galvanostatic pulse is applied to an Ag/AgCl electrode which initiates a faradic reaction depleting the Cl&#713; ions near the electrode surface. The transition time, which is the time to completely deplete the ions near the electrode surface, is a function of the ion concentration, given by the Nernst equation. The square root of the transition time is in linear relation to the chloride ion concentration. Drift of the response over two weeks is negligible (59 &#181;M/day) when measuring 1 mM [Cl&#713;]using a current pulse of 10 Am-2. This is a dynamic measurement where the moment of transition time determines the response and thus is independent of the absolute potential. Any metal wire can be used as a pseudo-reference electrode, making this approach feasible for long-term measurement inside concrete structures.

Die Ag / AgCl-Elektrode wird auf einem Glaschip hergestellt (Abbildung 1) eine Standard-Reinraum-Verfahren. Die chronopotentiometrischen Messaufbau (Abbildung 2) wurde verwendet, und die Reaktion wurde unter Verwendung eines Potentiostaten gemessen. Um die Wirkung der Cl-Ionenkonzentration an der Übergangszeit, Lösungen, die 4, 5 und 6 mM von Cl-Ionen in einer 0,5 M KNO 3 Hintergrund beobachten gemessen werden (Abbildung 3)....

Watch this Scientific Journal Video about Dynamic Electrochemical Measurement of Chloride Ions at JoVE.com

Dynamic Electrochemical Measurement of Chloride Ions

Dynamic measurement of chloride ions is presented. Transition time of an Ag/AgCl electrode, during a chronopotentiometric technique, can give the concentration of chloride ions in electrolyte. This method does not require a stable conventional reference electrode.

Dynamische elektrochemischen Messung von Chlorid-Ionen

This protocol describes the dynamic measurement of chloride ions using the transition time of a silver silver chloride (Ag/AgCl) electrode. Silver silver ...

dynamic-electrochemical-measurement-of-chloride-ions

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Electrochemical Analyses and Redox Titration

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11.4K Aufrufe.  University of Twente. Dynamic measurement of chloride ions is presented. Transition time of an Ag/AgCl electrode, during a chronopotentiometric technique, can give the concentration of chloride ions in electrolyte. This method does not require a stable conventional reference electrode.

Serie: Dynamic Electrochemical Measurement of Chloride Ions

Measurement of Ion Concentration in the Unstirred Boundary Layer with Open Patch-Clamp Pipette: Implications in Control of Ion Channels by Fluid Flow

Fluid flow is an important environmental stimulus that controls many physiological and pathological processes, such as fluid flow-induced vasodilation. Although the molecular mechanisms for the biological responses to fluid flow/shear force are not fully understood, fluid flow-mediated regulation of ion channel gating may contribute critically. Therefore, fluid flow/shear force sensitivity of ion channels has been studied using the patch-clamp technique. However, depending on the experimental protocol, the outcomes and interpretation of data can be erroneous. Here, we present experimental and theoretical evidence for fluid flow-related errors and provide methods for estimating, preventing, and correcting these errors. Changes in junction potential between the Ag/AgCl reference electrode and bathing fluid were measured with an open pipette filled with 3 M KCl. Fluid flow could then shift the liquid/metal junction potential to approximately 7 mV. Conversely, by measuring the voltage shift induced by fluid flow, we estimated the ion concentration in the unstirred boundary layer. In the static condition, the real ion concentrations adjacent to the Ag/AgCl reference electrode or ion channel inlet at the cell-membrane surface can reach as low as approximately 30% of that in the flow condition. Placing an agarose 3 M KCl bridge between the bathing fluid and reference electrode may have prevented this problem of junction potential shifting. However, the unstirred layer effect adjacent to the cell membrane surface could not be fixed in this way. Here, we provide a method for measuring real ion concentrations in the unstirred boundary layer with an open patch-clamp pipette, emphasizing the importance of using an agarose salt-bridge while studying fluid flow-induced regulation of ion currents. Therefore, this novel approach, which takes into consideration the real concentrations of ions in the unstirred boundary layer, may provide useful insight on the experimental design and data interpretation related to fluid shear stress regulation of ion channels.

Mechanosensitive ion channels are often studied in terms of fluid flow/shear force sensitivity with patch-clamp recording. However, depending on the experimental protocol, the outcome on fluid flow-regulations of ion channels can be erroneous. Here, we provide methods for preventing and correcting such errors with a theoretical basis.

Messung der Konzentration der Ionen in der ungerührte Grenzschicht mit offenen Patch-Clamp-Pipette: Auswirkungen auf die Kontrolle der Ionenkanäle durch Flüssigkeit fließen

Fluid flow is an important environmental stimulus that controls many physiological and pathological processes, such as fluid flow-induced vasodilation. ...

Forschung

Biochemie

Experimental Protocol to Determine the Chloride Threshold Value for Corrosion in Samples Taken from Reinforced Concrete Structures

The aging of reinforced concrete infrastructure in developed countries imposes an urgent need for methods to reliably assess the condition of these structures. Corrosion of the embedded reinforcing steel is the most frequent cause for degradation. While it is well known that the ability of a structure to withstand corrosion depends strongly on factors such as the materials used or the age, it is common practice to rely on threshold values stipulated in standards or textbooks. These threshold values for corrosion initiation (Ccrit) are independent of the actual properties of a certain structure, which clearly limits the accuracy of condition assessments and service life predictions. The practice of using tabulated values can be traced to the lack of reliable methods to determine Ccrit on-site and in the laboratory.
Here, an experimental protocol to determine Ccrit for individual engineering structures or structural members is presented. A number of reinforced concrete samples are taken from structures and laboratory corrosion testing is performed. The main advantage of this method is that it ensures real conditions concerning parameters that are well known to greatly influence Ccrit, such as the steel-concrete interface, which cannot be representatively mimicked in laboratory-produced samples. At the same time, the accelerated corrosion test in the laboratory permits the reliable determination of Ccrit prior to corrosion initiation on the tested structure; this is a major advantage over all common condition assessment methods that only permit estimating the conditions for corrosion after initiation, i.e., when the structure is already damaged.
The protocol yields the statistical distribution of Ccrit for the tested structure. This serves as a basis for probabilistic prediction models for the remaining time to corrosion, which is needed for maintenance planning. This method can potentially be used in material testing of civil infrastructures, similar to established methods used for mechanical testing.

We propose a method to measure a parameter that is highly relevant for corrosion assessments or predictions of reinforced concrete structures, with the main advantage of permitting testing of samples from engineering structures. This ensures real conditions at the steel-concrete interface, which are crucial to avoid artifacts of laboratory-made samples.

Experimentelles Protokoll den Chlorid-Schwellenwert für Korrosion in Proben aus Stahlbeton Strukturen bestimmen

The aging of reinforced concrete infrastructure in developed countries imposes an urgent need for methods to reliably assess the condition of these ...

Ingenieurwesen

Electrochemical Roughening of Thin-Film Platinum Macro and Microelectrodes

This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries of the metal. Using this method, a crack free, thin-film macroelectrode surface with up to 40 times increase in active surface area was obtained. The roughening is easy to do in a standard electrochemical characterization laboratory and incudes the application of voltage pulses followed by extended application of a reductive voltage in a perchloric acid solution. The protocol includes the chemical and electrochemical preparation of both a macroscale (1.2 mm diameter) and microscale (20 &#181;m diameter) platinum disc electrode surface, roughening the electrode surface and characterizing the effects of surface roughening on electrode active surface area. This electrochemical characterization includes cyclic voltammetry and impedance spectroscopy and is demonstrated for both the macroelectrodes and the microelectrodes. Roughening increases electrode active surface area, decreases electrode impedance, increases platinum charge injection limits to those of titanium nitride electrodes of same geometry and improves substrates for adhesion of electrochemically deposited films.

This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries. The electrochemical techniques of cyclic voltammetry and impedance spectroscopy are demonstrated to characterize these electrode surfaces.

ElektrochemischeS Schruppen von Dünnschicht-Platinmakro und Mikroelektroden

This protocol demonstrates a method for electrochemical roughening of thin-film platinum electrodes without preferential dissolution at grain boundaries ...

Chemie

Merging Ion Concentration Polarization between Juxtaposed Ion Exchange Membranes to Block the Propagation of the Polarization Zone

The ion concentration polarization (ICP) phenomenon is one of the most prevailing methods to preconcentrate low-abundance biological samples. The ICP induces a noninvasive region for charged biomolecules (i.e., the ion depletion zone), and targets can be preconcentrated on this region boundary. Despite the high preconcentration performances with ICP, it is difficult to find the operating conditions of non-propagating ion depletion zones. To overcome this narrow operating window, we recently developed a new platform for spatiotemporally fixed preconcentration. Unlike preceding methods that only use ion depletion, this platform also uses the opposite polarity of the ICP (i.e., ion enrichment) to stop the propagation of the ion depletion zone. By confronting the enrichment zone with the depletion zone, the two zones merge together and stop. In this paper, we describe a detailed experimental protocol to build this spatiotemporally defined ICP platform and characterize the preconcentration dynamics of the new platform by comparing them with those of the conventional device. Qualitative ion concentration profiles and current-time responses successfully capture the different dynamics between the merged ICP and the stand-alone ICP. In contrast to the conventional one that can fix the preconcentration location at only ~5 V, the new platform can produce a target-condensed plug at a specific location in the broad ranges of operating conditions: voltage (0.5-100 V), ionic strength (1-100 mM), and pH (3.7-10.3).

The protocol for a novel ion concentration polarization (ICP) platform that can stop the propagation of the ICP zone, regardless of the operating conditions is described. This unique ability of the platform lies in the use of merging ion depletion and enrichment, which are two polarities of the ICP phenomenon.

Zusammenführen von Ionenkonzentration Polarisierung zwischen Juxtaposed Ionenaustauschermembranen zu blockieren die Ausbreitung der Polarisations Zone

The ion concentration polarization (ICP) phenomenon is one of the most prevailing methods to preconcentrate low-abundance biological samples. The ICP ...

Biotechnik

Precise Electrochemical Sizing of Individual Electro-Inactive Particles

Nanoimpact electrochemistry enables the time-resolved in situ characterization (e.g., size, catalytic activity) of single nanomaterial units, providing a means of elucidating heterogeneities that would be masked in ensemble studies. To implement this technique with redox inactive particles, a solution-phase redox reaction is used to produce a steady-state background current on a disk ultramicroelectrode. When a particle adsorbs onto the electrode, it produces a stepwise reduction in the exposed electrode area, which produces, in turn, a stepwise decrease in the current commensurate with the size of the adsorbing species. Historically, however, nanoimpact electrochemistry has suffered from &#34;edge effects,&#34; in which the radial diffusion layer formed at the circumference of the ultramicroelectrodes renders the step size dependent not only on the size of the particle but also on where it lands on the electrode. The introduction of electrocatalytic current generation, however, mitigates the heterogeneity caused by edge effects, thus improving the measurement precision. In this approach, termed &#34;electrocatalytic interruption,&#34; a substrate that regenerates the redox probe at the diffusion layer is introduced. This shifts the rate-limiting step of the current generation from diffusion to the homogeneous reaction rate constant, thus reducing flux heterogeneity and increasing the precision of particle sizing by an order of magnitude. The protocol described here explains the set-up and data collection employed in nanoimpact experiments implementing this effect for improved precision in the sizing of redox in-active materials.

As an analytical technique, nanoimpact electrochemistry, an increasingly important approach to counting and characterizing nanometer-scale, electro-inactive particles, suffers from poor precision due to the heterogeneous current distributions that arise from its use of ultramicroelectrodes. Outlined here is a generalized approach, termed "electrocatalytic interruption," that enhances precision in such measurements.

Präzise elektrochemische Größenbestimmung einzelner elektroinaktiver Partikel

Nanoimpact electrochemistry enables the time-resolved in situ characterization (e.g., size, catalytic activity) of single nanomaterial units, providing a ...

Double-barreled and Concentric Microelectrodes for Measurement of Extracellular Ion Signals in Brain Tissue

Electrical activity in the brain is accompanied by significant ion fluxes across membranes, resulting in complex changes in the extracellular concentration of all major ions. As these ion shifts bear significant functional consequences, their quantitative determination is often required to understand the function and dysfunction of neural networks under physiological and pathophysiological conditions. In the present study, we demonstrate the fabrication and calibration of double-barreled ion-selective microelectrodes, which have proven to be excellent tools for such measurements in brain tissue. Moreover, so-called &#8220;concentric&#8221; ion-selective microelectrodes are also described, which, based on their different design, offer a far better temporal resolution of fast ion changes. We then show how these electrodes can be employed in acute brain slice preparations of the mouse hippocampus. Using double-barreled, potassium-selective microelectrodes, changes in the extracellular potassium concentration ([K+]o) in response to exogenous application of glutamate receptor agonists or during epileptiform activity are demonstrated. Furthermore, we illustrate the response characteristics of sodium-sensitive, double-barreled and concentric electrodes and compare their detection of changes in the extracellular sodium concentration ([Na+]o) evoked by bath or pressure application of drugs. These measurements show that while response amplitudes are similar, the concentric sodium microelectrodes display a superior signal-to-noise ratio and response time as compared to the double-barreled design. Generally, the demonstrated procedures will be easily transferable to measurement of other ions species, including pH or calcium, and will also be applicable to other preparations.

We demonstrate the fabrication, calibration and properties of two types of ion-selective microelectrodes (double-barreled and concentric) for measurement of ion concentrations in brain tissue. These are then used in the mouse hippocampal slice preparation to show that excitatory activity changes both extracellular potassium and sodium concentrations.

Doppelläufige und Concentric Mikroelektroden zur Messung der extrazellulären Ionensignale im Hirngewebe

Electrical activity in the brain is accompanied by significant ion fluxes across membranes, resulting in complex changes in the extracellular ...

Neurowissenschaften

A Micro-agar Salt Bridge Electrode for Analyzing the Proton Turnover Rate of Recombinant Membrane Proteins

To date, more than 50% of all pharmacological drugs target the transport kinetics of membrane proteins. The electrophysiological characterization of membrane carrier proteins reconstituted in lipid bilayer membranes is a powerful but delicate method for the assessment of their physicochemical and pharmacological properties. The substrate turnover number is a unique parameter that allows the comparison of the activity of different membrane proteins. In an electrogenic transport, the gradient of the translocated substrate creates a membrane potential that directly correlates to the substrate turnover rate of the protein. By using silver chloride electrodes, a diffusion potential, also called liquid junction potential, is induced, which alters electrode potential and significantly disturbs precise membrane potential measurements. Diffusion potential can be minimized by a salt bridge, which balances electrode potential. In this article, a micro-agar salt bridge is designed to improve the electrophysiological set-up, which uses micropipettes for the membrane formation. The salt solution is filled into a microcapillary pipette tip, stabilized by the addition of agarose, and can be easily mounted to a standard electrode. The electrode potential of a micro-salt bridge electrode is more stable compared to a standard electrode. The implementation of this system stabilizes electrode potential and allows more precise measurements of membrane potential generated by a pH gradient. Using this system, the proton turnover rates of the mitochondrial carriers UCP1 and UCP3 are reinvestigated and compared to earlier measurements.

In electrophysiological measurements, the presence of a diffusion potential disturbs the precise measurement of the reverse potential by altering the electrode potential. Using a micro-agar salt bridge, the impact of the diffusion potential is minimized, which allows a more precise measurement of substrate turnover numbers of reconstituted recombinant membrane proteins.

Eine Mikro-Agar-Salz-Brücke-Elektrode für die Analyse der Proton Fluktuationsrate von rekombinanten Membranproteine

To date, more than 50% of all pharmacological drugs target the transport kinetics of membrane proteins. The electrophysiological characterization of ...

A Proteoliposome-Based Efflux Assay to Determine Single-molecule Properties of Cl- Channels and Transporters

The last 15 years have been characterized by an explosion in the ability to overexpress and purify membrane proteins from prokaryotic organisms as well as from eukaryotes. This increase has been largely driven by the successful push to obtain structural information on membrane proteins. However, the ability to functionally interrogate these proteins has not advanced at the same rate and is often limited to qualitative assays of limited quantitative value, thereby limiting the mechanistic insights that they can provide. An assay to quantitatively investigate the transport activity of reconstituted Cl- channels or transporters is described. The assay is based on the measure of the efflux rate of Cl- from proteoliposomes following the addition of the K+ ionophore valinomycin to shunt the membrane potential. An ion sensitive electrode is used to follow the time-course of ion efflux from proteoliposomes reconstituted with the desired protein. The method is highly suited for mechanistic studies, as it allows for the quantitative determination of key properties of the reconstituted protein, such as its unitary transport rate, the fraction of active protein and the molecular mass of the functional unit. The assay can also be utilized to determine the effect of small molecule compounds that directly inhibit/activate the reconstituted protein, as well as to test the modulatory effects of the membrane composition or lipid-modifying reagents. Where possible, direct comparison between results obtained using this method were found to be in good agreement with those obtained using electrophysiological approaches. The technique is illustrated using CLC-ec1, a CLC-type H+/Cl- exchanger, as a model system. The efflux assay can be utilized to study any Cl- conducting channel/transporter and, with minimal changes, can be adapted to study any ion-transporting protein.

A Proteoliposome-Based Efflux Assay to Determine Single-molecule Properties of Cl- Channels and Transporters

Proteoliposomes are used to study purified channels and transporters reconstituted in a well-defined biochemical environment. An experimental procedure to measure efflux mediated by these proteins is illustrated. The steps to prepare proteoliposomes, perform the recordings, and analyze data to quantitatively determine the functional properties of the reconstituted protein are described.

Ein Proteoliposom Basierte Efflux-Assay auf Einzelmoleküleigenschaften von Cl Bestimmen<sup&gt; -</sup&gt; Kanäle und Transporter

The last 15 years have been characterized by an explosion in the ability to overexpress and purify membrane proteins from prokaryotic organisms as well as ...

Biologie

Measurement of Extracellular Ion Fluxes Using the Ion-selective Self-referencing Microelectrode Technique

Cells from animals, plants and single cells are enclosed by a barrier called the cell membrane that separates the cytoplasm from the outside. Cell layers such as epithelia also form a barrier that separates the inside from the outside or different compartments of multicellular organisms. A key feature of these barriers is the differential distribution of ions across cell membranes or cell layers. Two properties allow this distribution: 1) membranes and epithelia display selective permeability to specific ions; 2) ions are transported through pumps across cell membranes and cell layers. These properties play crucial roles in maintaining tissue physiology and act as signaling cues after damage, during repair, or under pathological condition. The ion-selective self-referencing microelectrode allows measurements of specific fluxes of ions such as calcium, potassium or sodium at single cell and tissue levels. The microelectrode contains an ionophore cocktail which is selectively permeable to a specific ion. The internal filling solution contains a set concentration of the ion of interest. The electric potential of the microelectrode is determined by the outside concentration of the ion. As the ion concentration varies, the potential of the microelectrode changes as a function of the log of the ion activity. When moved back and forth near a source or sink of the ion (i.e. in a concentration gradient due to ion flux) the microelectrode potential fluctuates at an amplitude proportional to the ion flux/gradient. The amplifier amplifies the microelectrode signal and the output is recorded on computer. The ion flux can then be calculated by Fick&#8217;s law of diffusion using the electrode potential fluctuation, the excursion of microelectrode, and other parameters such as the specific ion mobility. In this paper, we describe in detail the methodology to measure extracellular ion fluxes using the ion-selective self-referencing microelectrode and present some representative results.

Transporters in cell membranes allow differential segregation of ions across cell membranes or cell layers and play crucial roles during tissue physiology, repair and pathology. We describe the ion-selective self-referencing microelectrode that allows the measurement of specific ion fluxes at single cells and tissues in vivo.

Die Messung der extrazellulären Ionenflüsse Verwendung der ionenselektiven selbst verweisMikroElektroden-Technik

Cells from animals, plants and single cells are enclosed by a barrier called the cell membrane that separates the cytoplasm from the outside. Cell layers ...

Electrochemical Measurements of Supported Catalysts Using a Potentiostat/Galvanostat

Source: Laboratory of Dr. Yuriy Rom&#225;n &#8212; Massachusetts Institute of Technology
A potentiostat/galvanostat (often referred to as simply a potentiostat) is an instrument that measures current at an applied potential (potentiostatic operation) or measures potential at an applied current (galvanostatic operation) (Figure 1). It is the most commonly used instrument in the electrochemical characterization of anode and cathode materials for fuel cells, electrolyzers, batteries, and supercapacitors.
Conventionally, these anode and cathode materials are interfaced with a potentiostat via a three-electrode electrochemical cell. The electrode leads from the potentiostat are connected to the reference electrode, the counter electrode (often called the auxiliary electrode), and the working electrode (which contains the test material of interest). The electrochemical cell is then filled with a high ionic strength electrolyte solution, such as an acidic, alkaline, or salt solution. The media for this high ionic strength solution is typically aqueous; however, for applications necessitating higher operating cell potential windows, such as batteries and supercapacitors, non-aqueous media is often used. The cell media is degassed with an inert gas (to prevent unwanted side reactions) or with a test gas (if the test reaction involves a gas at one of the electrodes).
Alternatively, a salt bridge or membrane is employed to maintain ionic contact if the two half cells are to be measured in different electrolytes. In heterogeneous electrocatalysis, this type of &#34;two compartment&#34; cell is often used if the test molecule at the working electrode is also reactive at the counterelectrode. This happens frequently as the counterelectrode typically employed is platinum, which is a highly active catalyst for many reactions. Here, single compartment cells will be used, where all three electrodes are in the same media.
This video will explain the process of polishing a working electrode, preparing a catalyst ink, mounting the catalyst ink onto the working electrode, preparing the electrochemical cell, and then performing electrochemical measurements. The measurements that are performed include: cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronopotentiometry (CP), and chronoamperometry (CA).
<img alt="Figure 1" src="/files/ftp_upload/5698/5698fig1.jpg" /> 
Figure 1. An example of a single compartment electrochemical cell. a.) Teflon cap, b.) glass cell, c.) Pt wire counter electrode, d.) working electrode, e.) Ag/AgCl reference electrode, f.) 0.5 M aqueous sulfuric acid electrolyte solution.

Dynamische elektrochemischen Messung von Chlorid-Ionen

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