To quantify the concentration of lead Pb ions in a water sample using polarography, follow these steps:1. Sample preparation: Collect a representative water sample and filter it to remove any suspended particles. Acidify the sample with a few drops of concentrated nitric acid HNO3 to prevent the precipitation of lead salts and to stabilize the lead ions.2. Instrument setup: Set up the polarographic instrument, which typically consists of a dropping mercury electrode DME as the working electrode, a reference electrode e.g., Ag/AgCl or calomel electrode , and an auxiliary electrode e.g., platinum wire . Connect the electrodes to a potentiostat and a recorder or computer.3. Supporting electrolyte: Prepare a suitable supporting electrolyte solution, such as 0.1 M potassium chloride KCl or ammonium acetate NH4OAc . The supporting electrolyte provides a constant ionic strength and minimizes the resistance of the solution.4. Standard addition method: To improve the accuracy of the analysis, use the standard addition method. Prepare a series of standard solutions containing known concentrations of lead ions by diluting a stock solution of lead nitrate Pb NO3 2 . Add aliquots of the standard solutions to separate portions of the water sample, and measure the polarographic current for each addition.5. Polarographic measurement: Immerse the electrodes in the water sample or the standard solutions, and apply a potential sweep from a positive potential to a negative potential. The potential is applied in a linear or staircase manner, and the current is recorded as a function of the applied potential. The lead ions will be reduced at the dropping mercury electrode, producing a current peak at a characteristic potential.6. Calibration curve: Plot the peak current as a function of the added lead concentration for the standard solutions. The plot should be linear, and the slope of the line can be used to determine the sensitivity of the method.7. Sample analysis: Measure the polarographic current for the water sample, and determine the concentration of lead ions by comparing the current with the calibration curve. Correct for any background current or interferences by subtracting the current measured for a blank solution.8. Quality control: To ensure the accuracy and precision of the analysis, analyze a certified reference material or spiked samples with known concentrations of lead ions. The recovery of the spiked samples should be within an acceptable range e.g., 90-110% .By following these steps, you can quantify the concentration of lead Pb ions in a water sample using polarography.