Amperometrie

Amperometrie (amperometry) is an electrochemical method in which the current is measured while the potential of the working electrode is held constant. The measured current results from the oxidation or reduction of an electroactive species at the electrode surface. Under diffusion-controlled conditions, the steady-state current is proportional to the analyte concentration in the solution, enabling quantitative analysis.

In a typical setup, a potentiostat is used in a three-electrode cell comprising a working electrode (such as glassy carbon, platinum, or gold), a reference electrode (e.g., Ag/AgCl), and a counter electrode (usually platinum). The potential is chosen to drive the desired redox reaction of the target species. The current is recorded as a function of time to produce an amperometric response. When the potential is stepped to a fixed value, the technique is often referred to as chronoamperometry; the ensuing current decays over time as diffusion governs transport. For diffusion-controlled systems, the transient current follows the Cottrell relation i(t) = nFAD^1/2 C / (π t)^1/2, where n is the number of electrons transferred, F is Faraday's constant, A is the electrode area, D is the diffusion coefficient, and C is the bulk concentration.

Applications include enzyme-based biosensors (for example glucose sensors that generate a measurable current from enzymatically produced hydrogen peroxide), environmental monitoring of oxidizable species, and clinical analyses. Advantages are simplicity, fast response, and high sensitivity at low concentrations. Limitations include interference from other electroactive compounds, fouling of the electrode surface, and the need for careful calibration and stable reference electrodes.