Concentration of Electroactive Substance:
According to the Ilkovic equation,
id = Kc or id /c is constant keeping all other factors constant.
This is the primary of quantitative polarographic analysis. But there are objects while id/c is not constant and the current is determined through rate of chemical reaction (kinetic/ catalytic currents) and sometimes the adsorption of electroactive substance or its electrode reaction product (adsorption waves).