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The basic premise of polarography is the study of solutions or electrode processes using electrolysis with two electrodes, one polarisable and one non – polarisable. When a solution is electrolysed, the electrical characteristics such as emf, current, resistance, and so on are determined by the type and concentration of the different species present in the solution. This article will learn about the polarographic principle and application of polarography.
What Is Polarography?
Polarographic sensors serve as the foundation for field microelectrodes. However, field microelectrodes can also be Polarographic. Polarography, also known as electrochemical Polarography, is an electroanalytical method for determining the reduction potential of electroactive species.
Potentiometric techniques include polarographic methods such as coulometry, anodic stripping voltammetry, and atomic emission spectrometry. The concept is based on measuring the decrease in current or voltage that occurs in a polarisable electrolyte in contact with a polarised electrode. The ability of the electrode to become polarised is directly related to the activity of the material in the electrolyte.
Principle Of Polarography
- Polarography is based on applying a progressively rising voltage between two electrodes. One of these voltages is polarisable (dropping mercury electrodes) and the other non-polarisable, recording the current flowing between the two electrodes.
- A sigmoid-shaped current-voltage curve is used to calculate half-wave potential and diffusion current.
- Diffusion current is used to calculate the concentration of a chemical.
- The half-wave potential is a property shared by all elements.
Instrumentation
A cell or electrochemical cell, an electrode, and a potentiostat are the three major components of a polarographic device. In the case of the instrument’s probe, the potentiostat also functions as the electrode. A cell is an electrochemical cell with electrodes that stores a solution. Each electrode in a cell has one or more potentials applied to it, and each electrode has a potential used to it about another electrode in the cell. The probe is the instrument’s electrode. An electrode can function as both the working and counter electrode.
Ilkovic Equation
The Ilkovic equation is a polarography formula that connects the diffusion current (id) with the concentration of the non-polarisable electrode, i.e., the chemical reduced or oxidised at the falling mercury electrode (polarisable electrode).
(id)avg = 607 ncm2/3 t1/6 D1/2
Where,
id = Diffusion current in microamperes
607 = Constant of various numerical factors including: Faraday constant (П), density of Hg, etc
n = Number of electrons duly involved in the electrode reaction, D = Diffusion coefficient in cm² .sec-1 ,
m = Weight of Hg flowing via the capillary in mg.sec-1 ,
t = Drop time in seconds,
C = Concentration in mmol/L.
Applications Of Polarography
- Qualitative analysis: Using the half-wave potential of the current v/s voltage graph assists in characterising organic matter and other metal interactions.
- Qualitative analysis: Polarography determines the number of medicines, metal ions, and other substances in a particular sample.
- Inorganic compound determination: Polarography is used to determine cations and anions in the presence of interfering ions.
- Organic compound determination: Polarography determines organic chemical mixtures’ structure and quantitative analysis.
- Estimation of dissolved oxygen: Polarography may calculate the amount of oxygen dissolved in an aqueous solution or organic solvent.
- Pharmaceutical applications: Polarography can be used to analyse tetracycline antibiotics and sulphonamides.
Polarographic Analysis
Polarography is an electroanalytical method. It measures the current flowing between two electrodes in a solution. This approach is only practicable in the presence of an applied voltage that appears to grow steadily. This approach aims to identify the concentration of a particular solute and the type of solute. In analytical chemistry, polarography is also known as polarographic analysis.
Types Of Polarography
Direct Current Polarography
In Direct Current Polarography, a steady potential seems to be applied throughout the drop-life duration. It generates a current-voltage curve by employing a sequence of potential steps that are timed to coincide with the drop fall.
Square Wave Polarography
Whenever the potential between the working electrode and a reference electrode is swept linearly with time in Square Wave Polarography, the current existing in the working electrode is measured. The potential Waveform can be seen as a superposition of a conventional Square Wave onto an underlying staircase.
Normal Pulse Polarography
In Normal Pulse Polarography, the potential is modified not by a potential ramp that seems to ascend indefinitely but by Square Wave possible Pulses whose height increases and is overlaid over a constant initial potential.
Differential Pulse Polarography
Differential Pulse Polarography is often regarded as the most effective Pulse technique. In digital instruments, the excitation signal contains a rising Direct potential in the shape of a staircase. In an occasional series, tiny square wave pulses with a constant potential are applied to this rising direct potential. The current is measured twice: once before each pulse and again after the length of the pulse. The difference in readings seems to be plotted against the Direct potential, with the potential to yield peak-shaped polarograms.
Polarographic Cell
The polarographic cell is supposed to be advantageous in continuously examining changing conditions. When employing a polarographic cell for analysis, it should be designed with a low holdup volume at the flow rates being used, allowing for a quick response to changes in composition.
Conclusion
Polarography is a technique that is a part of voltammetric analysis. This technique is used to do qualitative and quantitative determination of electroactive substances. This article explains to you about polarographic principle and the application of polarography.
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