Polarographic Maxima: Maximum Suppressors:

Current-voltage curves acquired along with electro-reducible ions at DME are frequently distorted through increasing the current beyond the diffusion current value and rapidly reduce to the normal diffusion plateau after a critical value is reached as the applied potential is increased. That abnormal increase in current is referred as maxima and varies in shape from sharp peaks to rounded humps. To measure the true diffusion currents the maximum must be eliminated. This could be done through adding small amount of surface-active agents like as gelatin, dye stuff, Triton X-100 etc. that are likely to form an adsorbed layer on the mercury-solution interface to avoid streaming movement of the diffusion layer at the interface.

Gelatin is hugely used in the concentration range of 0.002 to 0.01 percent. Higher concentration will suppress the diffusion currents also. Others often used are, Triton X-100 (a non-ionic detergent) within the range of 0.002 to 0.004% and methyl cellulose (0.005%).

Figure: Polarogram of 2.3 mM lead (II)  in 0.1 M Potassium Chloride a)   In absence of a maximum suppresser b)   After addition of 0.0002% sodium methyl red.