Which chloride determination method uses coulometry-amperometry?

• A. ISE
• B. Cotlove chloridometry
• C. Whitehorn titration
• D. Schales and Schales

Answer: (B)

The method being tested relies on generating the titrant in place and measuring the electrical charge to quantify chloride. In this approach, a constant current is applied to a silver electrode to produce Ag+ ions in the solution. Those silver ions immediately react with chloride to form AgCl. As long as chloride is present, the generated Ag+ is consumed, so the current flow is tied to the chemical reaction. When all chloride has been consumed, further generation of Ag+ is no longer used by the reaction, and the charge passed up to that point directly reflects the amount of chloride in the sample (charge equals moles of chloride times Faraday's constant, with the 1:1 stoichiometry for Ag+ and Cl−).

This coulometry-amperometry approach is characteristic of Cotlove chloridometry. Other chloride methods, like ion-selective electrodes, measure chloride activity directly with a sensor rather than titrating by generating titrant electrochemically, and classic argentometric titrations (used in some older methods) rely on chemical titration with silver nitrate rather than electrochemical generation, so they do not use coulometry-amperometry.