10.15 : 制御電流クーロメトリー: 概要

Controlled-current coulometry, or amperostatic coulometry, uses a constant current for fast, straightforward analysis of the total charge produced during electrolysis by multiplying the current by the electrolysis time.

The setup includes a galvanostat, a two-electrode electrochemical cell, a clock for measuring the electrolysis time, and a switch to start and stop the process.

The analyte and electrolysis products on the counter electrode are separated with a salt bridge or porous frit.

Galvanostats are used because, during electrolysis, the analyte's declining concentration would cause the current to drop because fewer electrons are being generated.

So, the cell potential must be increased to maintain a constant current. However, other reactions may start at the generator electrode, and such reactions can reduce the current efficiency.

A 100% current efficiency can be achieved by adding an excess of a mediator, which produces ions that react quantitatively with the remaining analyte.

Alternatively, externally generated oxidizing or reducing reagents can be used.

The endpoint of the reaction can be indicated by visual indicators or through potentiometric or conductometric measurements.