Applications of the Polarographic Technique

The polarographic technique uses two electrodes, where one is polarised, and the other is unpolarised. The unpolarised electrode undergoes electrolysis on the surface of a dropping mercury electrode (DME) at an applied potential. This technique analyses the concentration of the solution. The DME is used as a working electrode for its wide range of cathodic action and its reusable electrode, where the flow of current with varied potential can be measured easily. The Faradic current (iF) and Capacitive current (iC) are the two components that play a major role in measuring the current flow. This article will learn about the polarographic technique, amphoteric principle, and application of amphoteric titrations. 

What Is Polarography?

Polarography is a voltammetric method that involves inorganic compounds (ions or molecules) that are oxidising (losing electrons) or reducing (gaining electrons) at the surface of a DME at an electric voltage. Polarography is only useful for the DME. The technique produces current-voltage curves from which the concentration of many lifeforms can be ascertained with good reproducibility even at very low concentrations.

Principles Under Polarography

• Amperometric Titration

A constant potential is maintained between the polarised indicator electrode and a depolarised reference electrode. The current flow on the electrode is measured at a regular increment in quantitative analysis.

• Voltammetric Principle

An electrochemical analysis where specific voltage is applied to the working and reference electrodes to determine the current flow through the electrolytic system.

• Working Electrode

It is the major component of the electrolytic process where the ions exchange and chemical reaction takes place. 

• Reference Electrode

It is the standard hydrogen electrode having zero electrode potential. 

Types of Polarographic Method

• Direct Current Polarographic

A constant potential will be applied during the entire drop-life time in this method. The current-voltage curve is drawn by considering the steps after consideration with drop fall. 

• Normal Pulse Polarography

This polarography is measured as a function of time and indicators, and reference electrodes. 

• Differential Pulse polarography 

Differential Pulse polarography is often known as differential pulse voltammetry and is also a process that is used to make electrochemical measurements. It is also a derivative of linear sweep voltammetry or staircase voltammetry. 

Application of Amperometric Titrations

1. Antiseptics and Insecticides

Insecticides like Gammexanes and parathion and Mercury-based antiseptics can be detected through amperometric titrations. With the help of polarography, Page and Waller determined the thimerosal content in vaccine preparation. Benesch has adopted this method to determine the phenylmercuric acetate in a gelatin base. Heptachlor Cyclohexane can also be reduced using the polarographic technique.

2. Vitamins

The polarographic technique can be applied to the following vitamins to determine the concentration in an aqueous solution   

• Aneurine
• Riboflavin
• Nicotinic acid
• Pantothenic acid 
• Pyridoxine
• Folic Acid
• Vitamin B12
• Ascorbic acid 
• α -tocopherol
• Vitamin K

  Aneurine and nicotinic acid can be found in liver extracts.

3. Hormones

     The following hormones can show polarograms on their determination

•  Thyroxine 
• Insulin
• Adrenaline
• Some Sex hormones     

4. Antibiotics

• Penicillin 
• Streptomycin
• Chloramphenicol

The antibiotics mentioned above use amperometric titration to plot polarograms.

5. Alkaloids

• Mostly alkaloids yield catalytic waves and few reductions in the titration process.
• Pech did a preliminary survey on quinoline and isoquinoline alkaloids yielded a catalytic wave in the presence of ammonium chloride solution.
• Some alkaloids with small catalytic waves are as follows: Isoquinoline alkaloids, Codeine, Morphine, Narcotine, and Hydrastine.

6. Blood, Serum, and Cancer Diagnosis

• Polarography is used in pathological sera.
• The unmasking of the disulphide bonds was done to partially hydrolysed the serum. 
• The filtrate of alkali-treated serum was precipitated with sulphosalicylic acid, and polarograms were noted on a buffer solution.

7. Miscellaneous Substances

• Polarograms can be plotted for the substances like sugar, saccharin, and iodine-containing contrast agents.
• Aldoses like rhamnose, arabinose, lyxoses, and glucose can be plotted using this technique.
• Some disaccharides like maltose, lactose, and sucrose produce small waves.
• Larger waves can be seen in ketoses such as fructose and sorbose.

Conclusion

A polarographic technique combines amperometric titration and voltammetric method. The electrolysis process is done by two electrodes, a polarised working electrode and an unpolarised reference electrode at an applied potential. DME is used if the working electrode has a wide cathodic action. It works on the two main amperometric principles. 

The increased current flow over a time between the two electrodes can be measured easily by amperometric titration and the specific current flow between the electrodes by voltammetric techniques. Few applications of amphoteric titrations are in antiseptics and Insecticides, vitamins, hormones, antibiotics, alkaloids, blood, serum, and cancer cells.