POLAROGRAPHY

INTRODUCTION :-  

The basic idea was to pass the current between two electrodes, one having large surface area and other having very small surface area. Both electrodes can be of mercury metal.  The large electrode can be a pool of mercury at the bottom of the cell.Small electrode is a drop of mercury coming out of a very fine capillary tube, DME.Thus, if a steady voltage is applied to such a cell, it is possible to construct a reproducible current voltage curve. 

POLAROGRAPHY DEFINATION :- 

Electro – analytical technique • Polarography is a method of analysis in which the solution to be analyzed is electrolyzed under diffusion controlled condition. • The graph of current (generated) as a function of voltage (applied) is known as POLAROGRAM. The technique is known as POLAROGRAPHY. • It can be used for qualitative as well as quantitative analysis (inorganic, organic and biological samples) without the requirement of prior separation step (in most of the cases).

HISTORY & BACKGROUND :- 

Polarography was created by Jaroslav Heyrovsky in Feb. 10th 1922.On December 10th 1959 he was awarded the Nobel Prize.

BASIC PRINCIPLE :- 

Polarography is based upon the principle that gradually increasing voltage is applied between two electrodes, one of which is polarisable (dropping mercury electrode) and other is non-polarisable and current flowing between the two electrode is recorded. Polarography has been used extensively to determine trace metals in pharmaceutical products and to estimate drugs that contain metals as a constituent. ... If the organic matter is reduced at the same or at a lower potential than that of the metal a preliminary chemical separation or ashing procedure must be undertaken.

WORKING :-

Electrolyte is a dilute solution of electro active material to be analyzed in a suitable medium containing excess of supporting electrolyte. • Consider a Polarographic cell, containing a solution of cadmium chloride, to which an external E.M.F is applied. • The positively charged ions present in the solution will be attracted towards the mercury drop of the dropping mercury electrode (DME). • The total current flowing through the cell may be regarded as being the “ sum of the electrical and diffusive forces.”

ADVANTAGES OF DME :- 

The advantages of DME over conventional diesel include decreased emissions of nitro gen oxides, hydrocarbons, particulate matter and carbon monoxide. Further, using DME as a fuel a significant combustion noise reduction is obtained. • Some of the advantages of dropping mercury electrode(DME) are as follows: Mercury form amalgam with most metals. Mercury has a high hydrogen overvoltage. It provides a smooth, fresh surface for the reaction. • The pool of mercury acts as a counter electrode, i.e., anode if DME is cathode or cathode if DME is the anode. The counter electrode is a non-polarisable electrode. 

LIMITATION OF DME:- 

The disadvantages a DME experiences due to a constantly changing surface are not experienced by the HMDE since it has static surface area during an experiment. The static surface of the HMDE means it is more likely to suffer from the surface adsorption phenomenon than a DME. • DME has low viscosity and a low boiling point, and smoke-free combustion can be obtained, since it has no carbon-carbon bond [2]. On the other hand, it has the disadvantage of low lubricity due to its low viscosity. When these fuels are blended together, the weaknesses of the fuels can be overcome.