Concept of electrochemical pH electrodes

Electrochemical pH electrodes are sensing devices designed to measure the concentration of hydrogen ions (H+) in a solution, allowing its acidity or alkalinity to be determined. They work based on electrochemical principles, generating an electrical potential proportional to the pH of the medium in which they are submerged.

These electrodes are essential in numerous scientific and industrial fields, since pH is a critical variable in chemical, biological and environmental processes. Their precision and speed make these electrodes essential tools for the control and analysis of aqueous solutions.

Electrochemical foundation of pH

The pH measures the activity of hydrogen ions in a solution, defined as the negative logarithm of said activity. pH electrodes convert this activity into a measurable electrical potential, based on the difference in concentration of H+ ions between the solution and a reference electrode.

The fundamental principle is based on the semipermeability of the pH-sensitive membrane, which allows selective interaction with hydrogen ions. This interaction generates a potential difference that is proportional to pH, which is detected and converted into an electrical signal.

This potential is measured in millivolts and its value is interpreted using the Nernst equation, which relates the electrical potential to the ionic concentration, allowing a precise measurement of pH.

Nernst equation applied to pH electrodes

The Nernst equation describes how the potential difference of an electrode depends on the concentration of ions in solution. For pH electrodes, it is expressed as: E = E0 - (RT/nF) ln [H+], where E is the measured potential, E0 is the standard potential, R is the gas constant, T the temperature in kelvin, n the number of electrons transferred and F the Faraday constant.