Potentiometry is an electroanalytical technique that measures the potential difference voltage between a working electrode indicator electrode and a reference electrode in a solution. In the case of determining the concentration of chloride ions in a water sample, the most common method is to use an ion-selective electrode ISE , specifically a chloride-selective electrode.Here is a step-by-step procedure to determine the concentration of chloride ions in a water sample using potentiometry:1. Prepare the chloride-selective electrode: A chloride-selective electrode is usually a silver-silver chloride Ag/AgCl electrode. It is sensitive and selective to chloride ions in the solution. Make sure the electrode is clean and properly conditioned according to the manufacturer's instructions.2. Prepare the reference electrode: A common reference electrode is the saturated calomel electrode SCE or silver-silver chloride Ag/AgCl electrode. The reference electrode provides a stable and constant potential.3. Calibration: Prepare a series of standard solutions with known concentrations of chloride ions e.g., 1, 10, 100 ppm . Measure the potential difference between the chloride-selective electrode and the reference electrode for each standard solution. Plot the measured potential differences mV against the logarithm of the chloride ion concentrations log [Cl-] . This will give you a calibration curve.4. Measure the potential difference of the water sample: Immerse the chloride-selective electrode and the reference electrode in the water sample. Allow the potential to stabilize and then record the potential difference mV .5. Determine the chloride ion concentration: Use the recorded potential difference of the water sample and the calibration curve to determine the concentration of chloride ions in the water sample. Locate the potential difference on the y-axis of the calibration curve, and then find the corresponding chloride ion concentration on the x-axis log [Cl-] . Convert the logarithmic value to the actual concentration.6. Perform quality control checks: To ensure the accuracy and reliability of the results, it is essential to perform quality control checks. These may include analyzing a known standard solution, a blank sample, and a spiked sample water sample with a known added concentration of chloride ions .By following these steps, potentiometry can be effectively used to determine the concentration of chloride ions in a water sample.