2.4. Polarógrafo EN



The quantitative and qualitative analysis of the species contained in a dissolution. It identifies and measures their concentrations from intensity curves.



A polarograph  is  essentially  an electrolytic cell, so it has necessarily to be formed by:

An electrode of mercury drop type, which is a very fine capillary tube through which mercury flows slowly and at a constant speed. This comes in the form of small drops.

A reference electrode, which can simply be a mercury deposit or a standard electrode of  calomel or platinum.

Another electrode, to which the dissolution of the electroactive substances, which we want to analyze, is added.

So that we can obtain the intensity curves, we have to add:

A power supply, which let us provide the cell with a variable potential.

A microammeter to measure the amperage generated during the electrolysis of the electroactive substances.


The polarographic cell is filled with the dissolution of the problem substance and the background electrolyte.  The electrodes are placed in the cell and nitrogen or helium flow through it to remove the dissolved oxygen which interfered with the measurements. Then, an electrical potential difference is applied. This way, an electrical current is generated. The electrical current intensity is measured with the microammeter, which is included in the device. In consecutive measurements, we increase the voltage and we register the new intensities. When we represent graphically the results, we obtain a sigmoidal curve (with an s shape) which will let us identify the substances contained in the dissolution and their level of concentration.


The polarography appeared when Jaroslav Heyrovsky invented the mercury droplet electrode in 1925.