Amperometric methods in water analysis are used to measure which parameter?

• A. Chlorine residual
• B. pH
• C. Turbidity
• D. Hardness

Answer: (A)

Amperometric methods determine how much of a substance is present by measuring the electrical current produced by a redox reaction at an electrode. In water analysis, chlorine residual is measured this way because chlorine species (like HOCl and OCl−) readily undergo oxidation/reduction at the sensing electrode, and the resulting current is directly proportional to the chlorine concentration. This makes amperometric sensors especially useful for online, continuous monitoring of residual chlorine in treated water.

Other parameters are detected with different approaches: pH is typically measured with a glass electrode using potentiometry, which monitors voltage rather than current; turbidity is assessed by optical methods such as nephelometry that measure light scattering; hardness is usually determined by titration or colorimetric/ion-specific methods rather than amperometry.