Wave height - concentration plots (calibration):

Prepare stock solutions of Cd²⁺ ion by dissolving 1.0 g of Cd²⁺ per dm³. From this take 1.0, 2.5, 5.0 and 10 cm3 into 100 cm³ volumetric flasks, add 50 cm³ of 2M KCl solution and 2.5 cm³ of 0.2% gelatin solution to each flask and then dilute to the mark with distilled water.

Take 10 cm³ of unknown solution (of about 0.04 g of Cd²⁺ per dm³) in a volumetric flask, add 50 cm³ 2M KCl and 2.5 cm³ of 0.2% gelatin solution and dilute to the mark with distilled water. Record the polarograms of four standard solutions and unknown after deaeration.

Let's draw calibration curve taking wave heights of all four standard solutions as ordinates and concentrations as abscissa. From this the concentration corresponding to wave height of unknown is remembered.