An electrochemical cell in potentiometry consists of two main components: an indicator electrode (working electrode) and a reference electrode. These components work together to measure the electrical potential (voltage) difference between them in the presence of an analyte in the sample solution. Here’s a brief overview of the components and their roles in the electrochemical cell for potentiometry:
1. Indicator Electrode (Working Electrode)
-Typically, manufacturers make the indicator electrode from a material selective to the ion or analyte of interest. They use different types of indicator electrodes based on the specific measurement requirements
– For pH measurements, a glass electrode is commonly used. It consists of a thin glass membrane that responds to changes in hydrogen ion (H+) concentration in the sample solution.
– Ion-selective electrodes (ISEs) are employed to measure the concentration of specific ions. For example, a fluoride-selective electrode measures fluoride ion (F-) concentration.
– In redox measurements, a metal electrode, such as a platinum or gold electrode, may be used.
2. Reference Electrode
– The reference electrode is a stable reference point for the potential measurement. It has a well-defined and constant potential.
Many potentiometric measurements commonly use the silver/silver chloride electrode (Ag/AgCl) as a reference electrode. It has a stable potential due to the reversible Ag/AgCl half-cell reaction.
– Other reference electrodes, depending on the specific application, include the saturated calomel electrode (SCE) and the silver/silver sulfide electrode (Ag/Ag2S).
3. Sample Solution
-The sample solution contains the analyte of interest, and you must determine its concentration using potentiometry
– The analyte concentration influences the potential measured by the indicator electrode in the sample solution. The potential difference between the indicator and reference electrodes changes as the analyte concentration changes.
Operation
-In the electrochemical cell, you immerse the indicator and reference electrodes in the sample solution.
– You measure the potential difference between the two electrodes using a potentiometer.
– The potential difference is related to the concentration of the analyte in the sample solution through the Nernst equation, which allows for determining the analyte’s concentration.
Designers of the electrochemical cell for potentiometry aim to maintain a stable and known potential at the reference electrode while enabling the indicator electrode to respond to changes in the ion concentration of the sample solution This allows for accurate and precise measurements of various analytes in different solutions. The specific design and components of the cell may vary depending on the type of potentiometric measurement and the targeted analyte.
Electrochemical electrodes are key components in potentiometry and other electrochemical techniques. Here, I’ll explain the construction and working principles of common reference electrodes (Standard Hydrogen Electrode, Silver Chloride Electrode, and Calomel Electrode) and indicator electrodes (metal electrodes and glass electrodes):
