Method of standard addition:
The Polarograms of unknown solution is first recorded as under (i) and a second polarogram is recorded by adding a known amount of the same ion.
Second polarogram:
Place 10 cm3 of unknown solution, 5 cm3 of known stock solution [of method (i)], 50 cm3 of 2M KCl and 2.5 cm3 of 0.2% gelatin solution in a volumetric flask and dilute to the mark with distilled water and record a polarogram of this solution in a polarographic cell after removing dissolved oxygen with nitrogen. Determine its wave height and calculate the concentration of unknown solution as elaborates under Unit 8 (polarography).