Depletion effect and precision of measurement in the digital polarography

The variation of diffusion current in the digital polarography decreases with 1/√n where n is the number of mercury drops at dropping mercury electrode. The variation of diffusion current in 10-3F solution of cadmium is 0.0005 as the coefficient of variation for the sum of the diffusion current of each drop from the first to the thirtieth drop, and also the same for the sum of the diffusion current from the tenth to the fifteenth drop with constant depletion effect. The plot of log i vs. log t on the current-voltage curve of the first drop is linear, but those of the second and subsequent drops are not linear because of the depletion effect which is greatest at an early stage of the drop life. The degree of the depletion effect is dependent on the outside diameter of capillary tip.