Polarography is an electroanalytical technique used to determine the concentration of an unknown substance in a given sample. It is based on the measurement of current as a function of applied potential in a solution containing the analyte of interest. The current is generated due to the reduction or oxidation of the analyte at a working electrode, usually a dropping mercury electrode DME or a static mercury drop electrode SMDE . The resulting current-potential curve, known as a polarogram, can be used to determine the concentration of the unknown substance.Here are the steps to determine the concentration of an unknown substance using polarography:1. Prepare the sample: Dissolve the unknown substance in a suitable solvent, usually an aqueous solution containing a supporting electrolyte to minimize the resistance of the solution and suppress migration effects.2. Set up the polarographic cell: The cell consists of a working electrode DME or SMDE , a reference electrode e.g., a saturated calomel electrode , and an auxiliary electrode e.g., a platinum wire . The electrodes are connected to a potentiostat, which controls the applied potential and measures the current.3. Record the polarogram: Apply a potential to the working electrode and gradually increase it. The current will increase as the potential approaches the reduction or oxidation potential of the analyte. The current will reach a maximum value, known as the limiting current, which is proportional to the concentration of the analyte.4. Calibration: Prepare a series of standard solutions with known concentrations of the analyte and record their polarograms. Plot the limiting current as a function of the concentration to obtain a calibration curve.5. Determine the concentration of the unknown substance: Measure the limiting current of the unknown sample and use the calibration curve to determine its concentration.Factors affecting the accuracy of the polarographic method:1. Temperature: The diffusion coefficient of the analyte and the viscosity of the solution are temperature-dependent, which can affect the limiting current and the shape of the polarogram.2. Purity of the reagents: Impurities in the supporting electrolyte or the solvent can cause additional peaks or background currents in the polarogram, leading to errors in the determination of the limiting current.3. Electrode surface: The cleanliness and condition of the working electrode can affect the reproducibility and accuracy of the measurements. It is essential to maintain a clean and well-functioning electrode.4. Stirring and convection: The mass transport of the analyte to the electrode surface can be affected by stirring and convection in the solution. It is crucial to maintain consistent stirring conditions for all measurements.5. Instrumental factors: The accuracy and precision of the potentiostat and the current measurement system can influence the quality of the polarogram and the determination of the limiting current.By carefully controlling these factors and following the proper experimental procedures, polarography can be a reliable and accurate method for determining the concentration of an unknown substance in a given sample.