Presentation on theme: "Polarography. Polarography is a subclass of voltammetry where the working electrode is a dropping mercury electrode (DME).voltammetryworking electrodedropping."— Presentation transcript:
Polarography is a subclass of voltammetry where the working electrode is a dropping mercury electrode (DME).voltammetryworking electrodedropping mercury electrode 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.
Hg will dropped in stable flow rate drops/min. Volts applied 50 – 200 mv/min Drop 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
Limiting current Diffusion current residual current Quantitative polarogram
Factors affecting diffusion current (Ilkovic equation) ½ m ί d = 708 n C D½ m ⅔ t ⅙ n : change in valency n : change in valency C : concentration C : concentration D : diffusion coefficient. D : diffusion coefficient. m: flow rate of mercury dropping. m: flow rate of mercury dropping. t : life time of mercury drop. t : life time of mercury drop.