1. Polarography

2. Polarography is a subclass of voltammetry where the working electrode is a dropping mercury electrode (DME). It is current versus potential are recorded when gradual changing current is take place when current applied to cell.

3. A cell containing :
Solution of interest (electroactive substance)
Stable reference electrode. e.g : calomel electrode.
Small area of indicator electrode (DME)
Auxiliary or counter electrode .

4. Mercury pool

5. Hg will dropped in stable flow rate 5- 30 drops/min.
Volts applied 50 – 200 mv/min
Drop life 2 – 12 sec.
Potential range (+ 0.4) – (-2) V

6. Advantage of Hg electrode
As the Hg capillary very narrow so, able to analyse very small volume of analyte.
Surface of electrode is very reproducible .
Surface area of electrode can be calculated from the weight of drops.

7. Disadvantage Limited potential (+0.4) – (-2) V.
Capillary is very small so easily to bloked .

8. Qualitative polarogram
Polarographic spectrum

9. Quantitative polarogram
Limiting current
Quantitative polarogram
Diffusion current
residual current

10. Factors affecting diffusion current
(Ilkovic equation)
ίd = 708 n C D½ m ⅔ t⅙
n : change in valency
C : concentration
D : diffusion coefficient.
m: flow rate of mercury dropping.
t : life time of mercury drop.