Polarography | Definition, Principle | Types, Instrumentation, Applications, Diagrams

What is polarography?

Polarography was first developed by Heyrovsky in 1922.

Polarography is an electrochemical method of analysis based on the measurement of current flow resulting from the electrolysis of a solution at a polarisable microelectrode as a function of applied voltage.

Principle of polarography:

Polarography is based upon the principle that gradually increasing voltage is applied between two electrodes, one of which is polarisable (dropping mercury electrode) anthe d other is non-polarisable and current flowing between the two electrodes is recorded.

A sigmoid shape current-voltage curve is obtained from which half wave potential, as well as diffusion current,nt is calculated.

Diffusion current is used for determination of concentration of the substance.

Instrumentation of polarography:

The instrumentation used in polarography typically consists of the following components:

Electrochemical cell:

This is a container where the solution to be analyzed is placed. It contains an electrode (usually a dropping mercury electrode) that is immersed in the solution.

Mercury reservoir:

This is a container that holds a pool of mercury. The electrode is dipped into the mercury pool, and a small droplet of mercury is allowed to form at the end of the electrode. This droplet is then used as the working electrode.

Reference electrode:

This electrode is used as a reference point for measuring the potential of the working electrode. A common reference electrode used in polarography is a saturated calomel electrode (SCE).

Potentiostat:

This is an electronic device that controls the potential applied to the working electrode. It ensures that the potential remains constant during the experiment and measures the resulting current response.

Recorder:

This is used to record the current response as a function of the applied potential. A chart recorder or computer-based data acquisition system can be used for this purpose.

Stirrer:

This is used to ensure that the solution in the cell is well-mixed and that the species being analyzed are evenly distributed throughout the solution.

Temperature control:

The temperature of the solution can affect the results of the experiment, so temperature control is important. This can be achieved by placing the cell in a temperature-controlled bath or using a temperature-controlled electrode.

In addition to these components, some polarography instruments may include additional features such as automatic sample injection or multiple working electrodes for simultaneous analysis of multiple samples.

Types of polarography:

There are several types of polarography, including:

Direct current (DC) polarography:

In this technique, a constant direct current is applied to the electrode, and the resulting potential is measured as a function of time. The resulting polarogram shows peaks corresponding to the reduction or oxidation of the species in the solution.

Differential pulse polarography (DPP):

In DPP, a small potential pulse is superimposed on a constant potential, and the resulting current response is measured. This technique provides higher sensitivity than DC polarography and is often used to analyze trace amounts of compounds.

Square wave polarography (SWP):

In SWP, a square wave potential is applied to the electrode, and the resulting current response is measured. This technique provides higher sensitivity than DC polarography and can be used to analyze both organic and inorganic compounds.

Alternating current (AC) polarography:

In AC polarography, an alternating current is applied to the electrode, and the resulting current response is measured. This technique is often used to analyze biological compounds such as proteins and nucleic acids.

Pulse voltammetry:

This technique involves the application of a series of potential pulses to the electrode and measuring the resulting current response. The resulting voltammogram provides information about the redox properties of the species in the solution.

Applications of polarography:

Polarography has a wide range of applications in various fields, including:

Analysis of inorganic ions:

Polarography is commonly used for the analysis of inorganic ions such as copper, zinc, and lead. By measuring the current-voltage relationship of a solution, the concentration of the ions can be determined. For example, the determination of trace amounts of lead in water samples is often done using polarography.

Analysis of organic compounds:

Polarography can also be used to analyze organic compounds such as vitamins, amino acids, and carbohydrates. By measuring the current-voltage relationship of a solution containing the organic compound, information about its electrochemical properties and concentration can be obtained.

Analysis of pesticides and herbicides:

Polarography can be used to determine the concentration of pesticides and herbicides in soil and water samples. For example, the analysis of organochlorine pesticides such as DDT in soil samples can be done using polarography.

Analysis of drugs:

Polarography can be used to analyze the concentration of drugs in biological samples such as blood and urine. This is useful in pharmacokinetic studies and drug development.

Analysis of electroplating solutions:

Polarography can be used to monitor the composition of electroplating solutions, which are used in the manufacture of electronic components. By monitoring the concentration of metal ions in the solution, the quality of the electroplated components can be ensured.

Analysis of food additives:

Polarography can be used to analyze the concentration of food additives such as preservatives and colorants. This is important for ensuring the safety and quality of food products.

Analysis of environmental pollutants:

Polarography can be used to analyze the concentration of environmental pollutants such as heavy metals and organic compounds in water and soil samples. This information is important for environmental monitoring and management.

Analysis of biological samples:

Polarography can be used to analyze the electrochemical properties of biological samples such as proteins, nucleic acids, and enzymes. This information is important for understanding the structure and function of these molecules.

Analysis of wastewater:

Polarography can be used to monitor the concentration of pollutants in wastewater. By measuring the current-voltage relationship of the wastewater sample, the concentration of pollutants such as heavy metals and organic compounds can be determined.

Quality control in pharmaceuticals:

Polarography can be used to monitor the quality of pharmaceutical products by analyzing the concentration of active ingredients and impurities. This is important for ensuring the safety and efficacy of pharmaceutical products.

Food and beverage analysis:

Polarography can be used to analyze the concentration of additives and contaminants in food and beverage samples. It can also be used to analyze the quality of alcoholic beverages.

Industrial process control:

Polarography can be used to monitor and control industrial processes such as electrochemical reactions and wastewater treatment. It can ensure that the process is operating within specified parameters and detect any deviations.

Overall, polarography is a versatile technique that can be used in a wide range of applications. Its sensitivity, selectivity, and accuracy make it a valuable tool for analytical chemists and researchers in many fields.