1

Polarography

BYDr. Suman PattanayakAssociate ProfessorDepartment of Pharma Analysis & QA.

Vijaya Institute of Pharmaceutical Sciences for Women

M. Pharm/ I SemAdvance Pharmaceutical Analysis

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.

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 .

Mercury pool

Hg will dropped in stable flow rate 5- 30 drops/min.

Volts applied 50 – 200 mv/minDrop life 2 – 12 sec.Potential range (+ 0.4) – (-2) V

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.

Disadvantage Limited potential (+0.4) – (-2) V.

Capillary is very small so easily to bloked .

Qualitative polarogram

Polarographic spectrum

Limitin

g current

Diffusion

current

residual

current

Quantitative polarogram

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