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DME and Polarographic Method

DME and Polarographic Method. By Jhon Ralph D. Enterina. Polarography. The earliest voltammetric technique Heyrovsky invented the original polarographic method in 1922, conventional direct current polarography (DCP).

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DME and Polarographic Method

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  1. DME and Polarographic Method By Jhon Ralph D. Enterina

  2. Polarography • The earliest voltammetric technique • Heyrovsky invented the original polarographic method in 1922, conventional direct current polarography (DCP). • It employs a dropping mercury electrode (DME) to continuously renew the electrode surface. • Diffusion is the mechanism of mass transport.

  3. Dropping Mercury Electrode (Working electrode) • Capillary tube about 10-15cm • Int. diameter of 0.05mm • A vertical distance being maintained betwwen DME and the solution • Drop time of 1-5 seconds • Drop diameter 0.5mm

  4. Advantages of DME • It limits the contamination or poisoning of the electrode surface. • Many metals are reversibly reduced to amalgam e.g. Cd2+ +2e- = Hg(Cd) • H has a high overvoltage at a mercury electrode • Drops are highly reproducible.

  5. Disadvantages of DME • Mercury is easily oxidized • Presence of nonfaradaic current • It tends to malfunction as a result of clogging • Oxygen is readily oxidized • Mercury is very toxic

  6. Polarogram • Limiting current- observed as plateau. It occurs when the mass transport rate is in its max. • Half- wave potential-potential at which the current is equal to one half of the limiting current(E1/2) • Residual current- a small current observed in the absence of the analyte. • Diffusion current- polarographic limiting current(id )

  7. Polarogram • Polarography measurement is governed by ilkovic equation: id= 708 nD1/2m2/3t1/6C • n= no. of electrons • t= droptime(second/drop) • D= diffusion coefficient of analyte (cm2/s) • m= rate of flow of Hg through capillary (mg/s) • C= analyte’s concentration in mM

  8. Polarogram

  9. Polarogram The oscillations at the limiting current are due to the drop of Mercury.

  10. Other Polarographic Methods Advantages Increased sensitivity Enhanced faradaic current Lower detection limit 10-7 to10-9 M Readily applicable for multi-component analysis • Pulse Polarography • Square-wave Polarography

  11. Application of Polarography • INORGANIC ANALYSIS • Analysis of metals • Zn • Cd • Analysis of anions as dromate, iodate, etc. • ORGANIC ANALYSIS • Analysis of carbonyl,peroxide, nitro, azo group, etc. • Biochemical analysis

  12. Old and Modern Polarograph

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