Polarography is an electroanalytical technique that measures the current-voltage relationship of a redox reaction to determine the concentration of a particular substance in a solution. It is widely used for the detection and quantification of trace elements, including heavy metal pollutants in water samples. Here is a step-by-step guide on how to determine the concentration of a substance using polarography:1. Prepare the sample: Collect the water sample and filter it to remove any suspended particles. If the sample is highly acidic or alkaline, adjust the pH to a suitable range usually between 4 and 8 using appropriate buffer solutions.2. Prepare the polarographic cell: The cell consists of a working electrode usually a dropping mercury electrode, DME , a reference electrode e.g., Ag/AgCl or calomel electrode , and an auxiliary electrode e.g., platinum wire . Fill the cell with the sample solution and add a supporting electrolyte e.g., KCl to maintain constant ionic strength and minimize the resistance of the solution.3. Set up the polarograph: Connect the electrodes to a potentiostat and a current measuring device e.g., a picoammeter . The potentiostat controls the potential applied to the working electrode, while the current measuring device records the current flowing through the cell.4. Perform the polarographic analysis: Apply a linearly increasing potential voltage to the working electrode and record the resulting current. The potential is increased from a value where no redox reaction occurs to a value where the analyte is fully reduced or oxidized. As the potential increases, the current will also increase due to the redox reaction of the analyte at the electrode surface.5. Analyze the polarogram: The resulting current-voltage plot is called a polarogram. The current will show a peak or a wave at the potential where the analyte is reduced or oxidized. The height of the peak is proportional to the concentration of the analyte in the solution.6. Calibration and quantification: Prepare a series of standard solutions with known concentrations of the analyte and perform polarographic analysis on each standard. Plot the peak current against the concentration of the analyte to obtain a calibration curve. Use this curve to determine the concentration of the analyte in the unknown sample by measuring its peak current and interpolating it on the calibration curve.Example: Determining the levels of heavy metal pollutants in a water sampleSuppose you want to determine the concentration of lead Pb in a water sample. Follow the steps mentioned above, and use a suitable supporting electrolyte e.g., 0.1 M KCl and a pH range that allows the reduction of Pb II ions to Pb 0 at the dropping mercury electrode. The polarogram will show a peak at the potential where Pb II is reduced to Pb 0 . Prepare a calibration curve using standard solutions of known Pb II concentrations and use it to determine the concentration of Pb II in the water sample. This technique can be similarly applied to other heavy metal pollutants, such as cadmium, mercury, and copper.