Electroanalytical Methods
Electroanalytical methods measure electrical quantities—potential, current, or charge—at electrodes to determine the identity and concentration of analytes.
Definition
Electroanalytical methods are analytical techniques that relate a measured electrical property at an electrode—potential, current, or accumulated charge—to the identity or concentration of an analyte in solution.
Scope
This area covers the analytical methods based on electrochemical measurement: potentiometry with ion-selective electrodes, the voltammetric and amperometric techniques that record current as a function of potential, and the coulometric and electrogravimetric methods that measure charge or deposited mass. It treats the cells, electrodes, and signal relationships used analytically; the broader thermodynamics and kinetics of electrochemistry belong to the electrochemistry subfield.
Sub-topics
Core questions
- How does an electrode potential report an ion's activity in potentiometry?
- How does a current–potential curve identify and quantify electroactive species?
- When does measured charge or deposited mass give a direct, calibration-free assay?
- What roles do reference electrodes and supporting electrolytes play in a measurement?
Key theories
- Nernst equation and potentiometry
- The potential of an indicator electrode depends logarithmically on the activity of the species it senses, as expressed by the Nernst equation; this relationship underlies potentiometric measurement with ion-selective electrodes, including the ubiquitous glass pH electrode.
- Faradaic current and electrolysis
- When an analyte is oxidized or reduced at an electrode, the current and total charge relate to the amount reacting; Faraday's laws make charge a direct measure of analyte quantity in coulometry, while the diffusion-limited current measures concentration in voltammetry.
Mechanisms
An electrochemical cell with indicator and reference electrodes converts chemical information into an electrical signal. In potentiometry, the equilibrium potential of an ion-selective electrode reports analyte activity with negligible current. In voltammetry and amperometry, a controlled potential drives oxidation or reduction and the resulting current measures concentration. In coulometry and electrogravimetry, the analyte is exhaustively electrolyzed and the charge consumed, or the mass deposited, quantifies it directly.
Clinical relevance
Electroanalytical methods are everywhere in routine measurement: pH and blood-gas and electrolyte analysis with ion-selective electrodes, glucose biosensors based on amperometry, trace-metal determination by stripping voltammetry, and water-quality and industrial process monitoring.
History
Electroanalytical chemistry rests on Nernst's late-19th-century relation between potential and concentration. Jaroslav Heyrovský's invention of polarography in 1922, for which he received the Nobel Prize, established current–potential measurement as an analytical tool, and later advances in pulse and stripping techniques and microelectrodes greatly extended sensitivity.
Key figures
- Walther Nernst
- Jaroslav Heyrovský
- Allen J. Bard
Related topics
Seminal works
- bard2001
- skoog2017
- harris2020
Frequently asked questions
- How does a pH meter work?
- A glass ion-selective electrode develops a potential that varies with hydrogen-ion activity according to the Nernst equation; measuring that potential against a reference electrode, after calibration with buffers, gives the pH.
- What is the difference between potentiometry and voltammetry?
- Potentiometry measures an equilibrium potential at essentially zero current to report ion activity, whereas voltammetry applies a varying potential and measures the resulting current to detect and quantify electroactive species.