Potentiometry is an analytical technique that measures the potential difference voltage between a working electrode indicator electrode and a reference electrode in a solution. In the case of fluoride determination in drinking water, an ion-selective electrode ISE for fluoride is used as the working electrode, and a stable reference electrode, such as a silver/silver chloride Ag/AgCl electrode, is used as the reference electrode.Here is a step-by-step procedure to quantify the amount of fluoride in a drinking water sample using potentiometry:1. Calibration: Prepare a series of fluoride standard solutions with known concentrations, typically ranging from 0.1 ppm to 10 ppm parts per million . These solutions can be prepared by diluting a fluoride stock solution, usually sodium fluoride NaF .2. Electrode preparation: Before using the fluoride ion-selective electrode ISE and the reference electrode, follow the manufacturer's instructions for electrode preparation, which may include soaking the ISE in a fluoride solution for a specific time.3. Calibration measurements: Measure the potential difference voltage between the fluoride ISE and the reference electrode for each standard solution. Stir the solution gently during the measurement to ensure homogeneity. Record the potential difference for each standard solution.4. Calibration curve: Plot the potential difference mV against the logarithm of the fluoride concentration log [F-] for each standard solution. The resulting calibration curve should be a straight line, according to the Nernst equation. Perform a linear regression to obtain the slope and intercept of the calibration curve.5. Sample preparation: Collect a representative drinking water sample and filter it if necessary to remove any particulate matter. The sample may need to be diluted if the fluoride concentration is expected to be outside the calibration range.6. Sample measurement: Measure the potential difference voltage between the fluoride ISE and the reference electrode in the drinking water sample, following the same procedure as for the calibration measurements.7. Calculate fluoride concentration: Using the potential difference obtained for the drinking water sample and the calibration curve equation, calculate the logarithm of the fluoride concentration log [F-] . Then, determine the fluoride concentration [F-] by taking the antilogarithm 10^x of the obtained value.8. Quality control: To ensure the accuracy of the results, analyze a quality control sample with a known fluoride concentration within the calibration range. The measured concentration should be within an acceptable range of the true value.By following these steps, you can quantify the amount of fluoride in a drinking water sample using potentiometry.