Polarography and Ilkovic equation

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

where:

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.

Interpretation:

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.

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.