Polarography
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Polarography. 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 :

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Polarography

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Polarography

Polarography


Polarography

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.


Polarography

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 .


Polarography

Mercury pool


Polarography

  • 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


Advantage of hg electrode

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

Disadvantage

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

  • Capillary is very small so easily to bloked .


Qualitative polarogram

Qualitative polarogram

Polarographic spectrum


Polarography

Limiting current

Quantitative polarogram

Diffusion current

residual current


Factors affecting diffusion current

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.


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