Polarography is a type of voltammetry where a dropping mercury electrode is used as the working electrode. A polarography cell contains an electrolyte solution, a reference electrode like calomel, a dropping mercury electrode, and an auxiliary electrode. As a potential is applied, the current is measured as mercury droplets fall through the solution. This allows for the analysis of electroactive substances and the production of polarograms that can be used for qualitative and quantitative analysis based on diffusion currents.

1. Presented by,
Nazzneen.MV
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. Limiting
current
Diffusio
n
current
residual
current
Quantitative polarogram

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.