The presence of fluoride ions in drinking water can be detected using a fluoride ion-selective electrode F-ISE . This method is based on the principle of potentiometry, which measures the potential difference between a reference electrode and an ion-selective electrode that is sensitive to the fluoride ions. The potential difference is proportional to the concentration of fluoride ions in the solution.To detect fluoride ions in drinking water using an ion-selective electrode, follow these steps:1. Prepare a series of fluoride ion standard solutions with known concentrations, typically ranging from 0.01 ppm to 10 ppm.2. Calibrate the fluoride ion-selective electrode by immersing it in the standard solutions and measuring the potential difference between the F-ISE and the reference electrode. Plot the potential difference against the logarithm of the fluoride ion concentration to obtain a calibration curve.3. Collect a water sample and, if necessary, filter it to remove any suspended particles.4. Adjust the pH of the water sample to around 5.5 using a buffer solution, as the fluoride ion-selective electrode is most sensitive in this pH range.5. Immerse the F-ISE and the reference electrode in the water sample and measure the potential difference.6. Compare the measured potential difference with the calibration curve to determine the concentration of fluoride ions in the water sample.The minimum detectable concentration of fluoride ions using the ion-selective electrode method depends on the sensitivity and selectivity of the electrode, as well as the quality of the calibration curve. Typically, the detection limit for fluoride ions using this method is around 0.01 ppm 10 ppb . However, more advanced electrodes and analytical techniques may achieve detection limits as low as 0.001 ppm 1 ppb .