Dme and polarographic method
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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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Dme and polarographic method

DME and Polarographic Method

By Jhon Ralph D. Enterina


Polarography

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.


Dropping mercury electrode working electrode

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


Advantages of dme

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.


Disadvantages of dme

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


Polarogram

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 )


Polarogram1

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


Polarogram2

Polarogram


Polarogram3

Polarogram

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


Other polarographic methods

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


Application of polarography

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


Old and modern polarograph

Old and Modern Polarograph


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