amperometry

Amperometry is an electrochemical technique in which current is measured while the potential of an electrode is fixed with respect to a reference electrode. The measured current results from oxidation or reduction of electroactive species at the working electrode surface and is proportional to the rate of electron transfer at that interface. At suitable potentials the current is often diffusion controlled, and for planar diffusion a Cottrell-type relationship describes the time dependence of the current: i(t) = n F A C sqrt(D / (pi t)).

In a typical amperometric experiment, a potentiostat controls a working electrode in a three-electrode cell with a reference and a counter electrode. After applying a fixed potential, current is recorded over time. Chronoamperometry employs a potential step, and at steady state the current is governed by diffusion to the electrode surface. Microelectrodes or rotating disk electrodes help achieve steadiness by enhancing mass transport, improving response time and sensitivity.

Applications and limitations: Amperometry is widely used for trace analysis of electroactive species, in clinical diagnostics and biosensors (for example glucose sensors) and environmental monitoring. It enables rapid, inexpensive measurements with good sensitivity when the electrode surface is selective. Limitations include interference from other redox-active substances, fouling of the electrode surface, and slower responses for species with slow electron-transfer kinetics or poor diffusion.