Voltammetry and Amperometry

Voltammetry and amperometry measure the current produced when an analyte is oxidized or reduced at an electrode to identify and quantify electroactive species.

Definition

Voltammetry and amperometry are electroanalytical methods that record the current arising from the oxidation or reduction of an analyte at an electrode as a function of, or at a fixed, applied potential, relating that current to analyte concentration.

Scope

This topic covers controlled-potential techniques: polarography and its pulse variants, linear-sweep and cyclic voltammetry, hydrodynamic voltammetry, stripping analysis, and steady-state amperometric detection. It treats the three-electrode cell, the shape and origin of current–potential curves, diffusion-limited currents, and the use of preconcentration in stripping methods to reach very low detection limits.

Core questions

• How does a current–potential curve identify an electroactive species and measure its concentration?
• Why is the limiting current proportional to concentration in many voltammetric methods?
• How does anodic stripping preconcentrate trace metals to lower detection limits?
• How does amperometric detection turn an electrode into a selective sensor?

Key theories

Diffusion-limited current

When the applied potential is sufficient to react the analyte as fast as it arrives, the current is limited by diffusion to the electrode and becomes proportional to analyte concentration; this proportionality, captured by relations such as the Cottrell and Levich equations, makes voltammetry quantitative.

Polarography at the dropping mercury electrode

Heyrovský's dropping mercury electrode produces reproducible current–potential waves whose half-wave potential identifies a species and whose wave height measures its concentration, founding the family of voltammetric methods.

Mechanisms

In a three-electrode cell, a potentiostat applies a controlled potential to a working electrode and measures the resulting current while a reference electrode fixes the potential scale. As the potential is swept or stepped, an electroactive analyte is oxidized or reduced, producing a current that rises to a diffusion-controlled plateau or peak whose position identifies the species and whose magnitude measures concentration. Stripping methods first deposit the analyte onto the electrode, then strip it back, amplifying the signal for trace determination.

Clinical relevance

Amperometric and voltammetric methods power glucose and other enzyme biosensors, oxygen sensors, and electrochemical detectors in liquid chromatography, while stripping voltammetry provides sensitive trace-metal analysis for environmental and clinical samples.

History

Voltammetry began with Heyrovský's 1922 invention of polarography using the dropping mercury electrode, recognized with the Nobel Prize. Later developments—pulse polarography, cyclic voltammetry, rotating-disk hydrodynamics, stripping preconcentration, and microelectrodes—extended sensitivity and broadened the technique into mechanistic study and sensing.

Key figures

• Jaroslav Heyrovský
• Allen J. Bard
• Veniamin Levich

Seminal works

• heyrovsky1922
• bard2001
• skoog2017

Frequently asked questions

What is the difference between voltammetry and amperometry?

Voltammetry records current while the potential is varied, producing a current–potential curve, whereas amperometry holds the potential fixed and monitors current over time, which suits continuous detection and sensing.

Why is stripping voltammetry so sensitive?

It first deposits and concentrates the analyte onto the electrode over a controlled time, then measures the current as that accumulated material is stripped off, so even trace concentrations give a large, measurable signal.