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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. A cell containing :

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Polarography

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  1. 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 Quantitative polarogram Diffusion current residual current

  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.

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