Polarography is a type of voltammetry where the working electrode is a dropping mercury electrode (DME). A polarographic cell contains a solution of interest, a reference electrode like calomel, a small DME indicator electrode, and an auxiliary electrode. Mercury is dropped from the DME at a stable rate, and current versus potential is recorded as voltage is applied gradually. The DME allows for analysis of very small sample volumes due to its narrow capillary. However, polarography is limited to potentials between +0.4 and -2 V, and the small capillary can become blocked. The diffusion current in polarography depends on factors like analyte concentration, diffusion coefficient, mercury drop flow rate, and drop lifetime

1. 1
Polarography
BY
Dr. Suman Pattanayak
Associate Professor
Department of Pharma Analysis & QA.
Vijaya Institute of Pharmaceutical Sciences for Women
M. Pharm/ I Sem
Advance Pharmaceutical Analysis

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.