Amperometry is another analytical technique involving electrolysis: The current that flows at constant potential between the corresponding pair of electrodes is measured, because if one of the substances involved in this electrolysis is the analyte to be quantified, the measurable current is proportional to the analyte concentration (although here, too, the system must of course be calibrated); a material that is as chemically inert as possible, such as platinum, gold or even carbon, again serves as the counter or working electrode.