About polarography and its types.

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.