Polarography

• Polarography is an electroanalytical technique introduced by Jaroslav Heyrovsky in 1922.
• It measures the current-potential (I-V) relationship by applying a gradually increasing voltage to a working electrode in a solution containing the analyte.
• The current results from redox reactions at the electrode surface.

Principle of Polarography

• Polarography is based on measuring current as a function of applied potential to study the electrochemical behavior of chemical species.
• The technique focuses on redox reactions at the surface of a working electrode when the potential is varied.

Key Components of Polarography:

1. Working Electrode: Usually a dropping mercury electrode (DME) or static mercury drop electrode (SMDE).
2. Reference Electrode: Maintains a stable, known potential.
3. Counter Electrode: Completes the circuit.
4. Sample Solution: Contains the analyte and supporting electrolyte.
5. Potentiostat: Controls potential and measures current.

Steps in Polarographic Experiment:

1. Electrodes are immersed in the sample solution.
2. A linearly changing potential is applied to the working electrode.
3. Redox reactions occur at specific potentials, generating a current.
4. The current is plotted against potential to form a polarogram, which shows peaks or steps indicating the concentration and behavior of analytes.

Ilkovic Equation

• The Ilkovic equation relates the diffusion current measured in a polarographic experiment to the concentration of the electroactive species (analyte) in solution.
• It was derived by Slovak chemist Dionýz Ilkovič in 1934.

i_d = 2.69 × 10⁵ × n × √D × C × d

Where:

• id​ = diffusion-limited current (in microamperes, µA)
• n = number of electrons transferred in the redox reaction
• D = diffusion coefficient of the analyte (in cm²/s)
• C = concentration of the analyte (in mol/cm³)
• d = diameter of the mercury drop (in cm)

This equation is particularly applicable to a Dropping Mercury Electrode (DME), where the mercury drop grows and detaches from the electrode at regular intervals. The Ilkovic equation assumes steady-state conditions with diffusion as the primary mass transport mechanism, and negligible effects from migration and convection.

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