Electroanalytical methods measure a sample's chemical properties, concentration especially, through electrical signals, voltage, current or resistance, that change in a predictable, measurable way as the target substance's concentration in the sample actually changes. A standard pH meter is the most familiar everyday example of the whole technique family, an electrode dipped into a sample producing a voltage reading a chemist converts directly into a concentration figure.
An electrode's measurable signal changes in a known way with concentration
Electroanalytical methods place one or more electrodes in contact with a sample, and the electrical property being measured changes according to a known, quantifiable relationship with the target substance's concentration. In potentiometric methods, including the standard pH electrode, that relationship is described by the Nernst equation, which links a measured voltage directly to the concentration of the specific ion the electrode responds to, giving a chemist a way to convert an electrical reading straight into a concentration figure.
Different specific techniques suit different analytes and concentration ranges
Potentiometry, exemplified by pH meters, measures voltage under conditions where essentially no current flows. Voltammetry and amperometry instead measure current, either at a controlled fixed voltage or while deliberately varying it, suited to analytes that undergo a specific electrochemical reaction at the electrode. Conductometry measures a sample's overall electrical conductivity rather than targeting one specific ion, useful for tracking general changes in a solution's total ion concentration. Each technique suits genuinely different analytes and concentration ranges, which is why a chemist picks the specific method to fit the specific measurement problem.
What we're still unsure about
That electroanalytical methods rely on a known, quantifiable relationship between an electrical signal and concentration is well established, uncontroversial analytical chemistry. What's more genuinely a practical, ongoing concern is that electrodes drift and foul with continued use, their measured response gradually changes over time as the electrode surface itself degrades or gets coated by residue from the samples it's measured, which means electroanalytical instruments need frequent recalibration against known standards, and exactly how often recalibration is genuinely needed for a specific electrode and sample type is more a matter of accumulated practical experience than one universal, settled rule.
This sits inside Electroanalytical Methods, one of seven topics in Analytical Chemistry, one of six domains in Chemistry, one of seventeen subjects the app can quiz you on.