Polarography and Ilkovic equation

Polarography and Ilkovic equation

What is Polarography? 

  • Polarography is an electrochemical technique used to measure the concentration of certain substances in a sample.
  • It is based on the principle of electrochemical reduction and oxidation reactions that occur at an electrode surface.
  • In polarography, a sample is placed in a cell containing an electrolyte solution and two electrodes: a working electrode and a reference electrode.
  • A potential is applied between the electrodes, and the current passing through the cell is measured as a function of the applied potential.
  • As the potential is varied, different electrochemical reactions occur at the working electrode, leading to changes in the current.
  • The current-potential curve obtained in polarography is called a polarogram.
  • By analyzing the shape and position of the polarogram, it is possible to determine the concentration of the substance of interest in the sample.
  • Polarography is a versatile and widely used technique in analytical chemistry, and it has applications in various fields, including environmental monitoring, pharmaceutical analysis, and industrial quality control.
  • It is particularly useful for measuring the concentration of substances that undergo electrochemical reactions, such as metal ions, organic compounds, and dissolved gases.

The Ilkovic equation

  • Ilkovic equation relates the diffusion current (id) measured in polarography to the concentration (C) of the electroactive species in the electrolyte solution. It is named after Dionýz Ilkovič, a Slovak chemist, who derived the equation in 1934.

Here’s the formula for the Ilkovic equation:

id = 607nFDm^(1/2)t^(1/2)C


  • id: Diffusion current (in amperes, A)
  • n: Number of electrons transferred in the electrode reaction (dimensionless)
  • F: Faraday constant (96485 C/mol)
  • D: Diffusion coefficient of the electroactive species (in cm²/s)
  • m: Mass flow rate of the mercury electrode (in mg/s)
  • t: Drop time of the mercury electrode (in seconds)
  • C: Concentration of the electroactive species (in mmol/L)

Understanding the terms:

  • Diffusion current: The current measured in polarography that arises due to the diffusion of the electroactive species towards the electrode surface.
  • n: The number of electrons involved in the reduction or oxidation reaction occurring at the electrode.
  • F: A constant value representing the amount of charge per mole of electrons.
  • D: A measure of how quickly the electroactive species can move through the solution.
  • m: The rate at which mercury flows from the capillary tip forming the dropping mercury electrode (DME).
  • t: The time it takes for a mercury drop to fall from the DME.
  • C: The concentration of the electroactive species in the solution.


The Ilkovic equation shows that the diffusion current is proportional to:

  • The square root of the diffusion coefficient (D) and the drop time (t) – This indicates that the current increases as the diffusion rate and the time available for diffusion increase.
  • The number of electrons transferred (n) – More electrons transferred per molecule lead to a higher current.
  • The concentration of the electroactive species (C) – Higher concentrations lead to more molecules available for the reaction, resulting in a larger current.

Applications of Polarography and Ilkovic equation

The Ilkovic equation has various applications in analytical chemistry, including:

  • Quantitative analysis: Determining the concentration of electroactive species in a solution by measuring the diffusion current.
  • Characterizing electrode reactions:Understanding the number of electrons involved in the reaction and the rate of electron transfer.
  • Studying reaction mechanisms:Investigating the role of diffusion and other parameters in the overall reaction process.

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