Polarographic Cell

Polarography is a voltammetric analysis that uses electrodes. It is an electrode’s qualitative and quantitative qualities. This analysis can also be done through a polarographic cell. The Polarographic cell is thought to be used for continuous flow analysis. When using a polarographic cell for analysis, it should be designed to have a low holdup volume about the flow rates used, allowing for a faster response to changes in composition. This article will learn about polarographic cells, liquid-liquid junction potential, and its formula. 

Polarography

Reducible and oxidisable substances are determined qualitatively and quantitatively through a chemical analysis called Polarography. This analysis observes the nature of the solution through two electrodes of a cell, one of which can be polarised and the other cannot be polarised. The former is generated by dropping mercury from capillary tubes. 

Polarographic Cell

Evaluated potentials in polarography and some potentiometric analysis are taken as the saturated calomel electrode (S.C.E.) rather than the hydrogen electrode. Polarography accomplishes this in one of three ways:

Polarograms are documented with the mercury pool serving as a reference electrode, and half-wave possibilities are corrected by the value obtained by measuring the pool’s potential concerning the S.C.E. An S.C.E., or another suitable reference electrode is used as a counter electrode. The electrode’s area is made as large as possible to reduce the current polarisation of the reference electrode.

Two working electrodes and a reference electrode, usually an S.C.E., are used. The potential is measured between the microelectrode and the reference electrode. At the same time, a current is passed among the microelectrode and a counter electrode. Polarograms are created by plotting microelectrode current versus reference electrode-micro electrode potential.

The first two methods produce the most polarographic data, especially in aqueous solutions. Because of the appropriate power drop in the cell caused by the current flowing through the cell’s internal resistance, the observed half-wave potential is always more significant than the actual value in both methods.

If the cell is designed correctly, this error can be reduced to negligible levels. When the internal cell resistance cannot be reduced sufficiently (to about 1000 or less), as with specific immiscible solutions, the evident shift in half-wave potential must be corrected before comparing half-wave potentials.

The resistance of the cell in the two-electrode polarographic cells must be evaluated under dynamic conditions in the area of the half-wave potential, and suitable adjustments must be calculated. The correct cell design and placement of the electrode in close vicinity to the microelectrode in the case of the three-electrode polarographic cell will yield an indeed corrected polarogram without the need for a cell measurement method.

The primary contributor to the development of analog computer-type amplifiers to be used as elements in electro-analytical synthetic equipment. These simple, dependable elements make it relatively simple to design and operate exact, stable instruments with a rapid response for potential or current control, as well as many other applications.

Liquid Junction Potentials Measurement and Correction

The diffusion potential or liquid junction potential is present in any potential measurement involving cells with liquid junctions, such as those using an S.C.E. In most cases, the magnitude of this potential can be reduced to a negligible value by selecting the appropriate salt bridge with cation and anion mobilities that are equal. 

The liquid junction in simple cases with aqueous solutions can be measured as well as calculated theoretically.

The liquid junction potential in simple cases with aqueous solutions can be assessed and determined from existing theories. The quantification or computation of the liquid junction among an aqueous and a nonaqueous solution has become highly complex and is accomplished using standard means.

Nelson advises oxidising the 4.7-dimethyl-1,10-phenanthroline complex of iron(II) to the same complex of iron(III) as the reference couple. In contrast, Koepp and Coetzee recommend using the Rb+ + Rbo as the standard reference. 

Liquid Junction Formula

Liquid junction formula is 

Em=Eref+Em+Ejunction

The Ejunction in aqueous solutions can be reduced by selecting the correct salt bridge electrolyte. The problem becomes more complicated when polarographic measurements are performed with solvents other than water. There can be no comparisons of the relative values of potentials in different solvents without knowing the magnitude of the liquid junction potential.

Conclusion

A Polarographic cell is an arrangement used to analyse substances. For the analysis to occur, the polarographic cell should be used to have a lower hold-up volume than the initial rates. This article has taught about polarographic cells and liquid junction potential.