Polarography:

The polarographic method of analysis was developed through Jaroslav Heyrovsky in 1922 that is the earliest voltammetric technique introduced.  He received Nobel Prize within 1952 for developing this method using dropping mercury electrode as the working electrode.  Jaroslav Heyrovsky called the recorded current-potential curves as polarograms and introduced the term polarography.

As to Ilkovic equation, i_d is proportional to concentration keeping all other factors of the equation constant. So, if some of the electroactive material in the solution is removed by interaction with some other reagent (e.g. EDTA reagent for Zn²⁺ determination) the diffusion current will decrease. That is the fundamental principle of amperometric titrations or polarographic titrations.

Most metal ions are reducible at DME, and multicomponent  mixtures can often be analysed by selecting an appropriate supporting electrolyte so that the half-wave potentials of the two ions are differed by about - 0.2 V vs SCE or by using complexing agents by taking the advantage of complexing ability of the metal ions. Based on this, polarography is used predominantly for trace metal analysis of alloys, ultra-pure metals, minerals/metallurgy, environmental analysis (air, water, soil and sea water contaminant), beverages, foodstuffs, and body-fluids, toxicology and clinical analysis. Reducible anions such as BrO₃^-, IO₃^-, Cr₂O₇^2- and NO₂^- can also be determined using well buffered solutions.