3. Introduction
• Discovered by Jaraslove Heyrosky in 1922,
• Who received Nobel prize in chemistry in 1952.
• The term polarography is applied to the
current voltage curve when dropping mercury
electrode is used and indicator electrode.
• This method comes under the category of
voltammetry techniques.
4. Principle:
• Polarography can be applied by increasing
negative potential between polorisable. and
depolrisable. electrode.
• Current voltage curve is recorded in sigmoid
shape
• The instrument which is use which is known
as polarograp.
• The current voltage curve is recorded which is
known as polarogram.
• Polarogram
6. Types of current :
1. Residual current
2. Migration current
3. Diffusion current
4. Limiting current
7. 1. Residual current:
• It is the sum of the faradic current and
condenser current.
• Current produced by traces of the impurities
or reduction of the impurities.
• Condenser Current produced by Helmholtz
double layer.
• Residual current is denoted by (ir).
8. 2: Migration current
• Migration current is due to cation from
the bulk of the solution towards the
Cathod due to diffuse force.
• This current is due to migration of
oxidizable and reducible ion which is
proportional to the potential gradient.
• This can be removed by the addition of
supporting electrolyte solution.
9. 3 : Diffusion current
• Diffusion current is due to actual diffusion of
eletroreduciable ion from the bulk of sample
to the surface of the mercury droplet due to
concentration gradient.
• Various factors can be affected by the
diffusion of current.
10. 4: limiting current.
• Beyond a certain potential the current
reaches a steady value called as limiting
current.
• At this point the rate of diffusion of ion
is equal to rate of reduction.
• State of electrode is said to be
concentration polarised.
12. Construction and working:
1. Dropping mercury electrode.
2. Supporting electrolyte.
3. Mercury pooled
4. Capillary tube.
13. Dropping mercury electrode:
• The indicator electrode is use for the analyte of
sample in the response of potential.
• Dropping mercury electrode is use as indicater
electrode.gradully increasing negative potential
can be applied easily.
• Known as working electrode.
• The basic principles of this dropping mercury
electrode is to control mercury flow through the
capillary closed the neddle valve.
15. Advantages
• It provides a smooth and fresh surface for the
reaction.
• Mercury forms amalgam with most metals.
• Mercury has high hydrogen overvoltage.
• Each drop remains unaffected and does not
contaminated by the deposit ed metals.
• It useful the range of +0.4 to -1.8 volt.
16. Disadvantages:
• Surface area of drop of mercury has never
constant.
• Mercury has a poisonous.
• Applied voltage produces change in
surface tension and change in drop size.
17. Capillary tube:
• The capillary is glass tube and internal
diameter is 20-50u and connect ed to
mercury reservoir.
• By adjusting the height of the reservoir the
drop time can also adjusted.
• The drop size depends on the bore size of the
capillary.
18. Mercury pooled:
• A large pooled of mercury at bottom of the cell
is a anode and act as reference electrode.
• Saturated calmol electrode is also use.
• By connecting the pooled of mercury.
19. IIkovic equation
• The diffusion current at the SAME is given by
llkovic equation:
• id= 607n c m t
• Various factors can affect the llkovic equation.
• The quantities of mass ,and time will vary with
the capillary and the pressure of the mercury.
20. Half wave potential:
• Half wave potential is defined as the difference
between the total current to the total residual
current which is equal to the one half of the
limiting current.
• This can be obtained from theCVC.
• This can be mainly use for the identification of
the substance.
21. Application :
• Qualitative and quantitative analysis.
• Turbid and colour sample will be analysed.
• Mixture of sample will be analysed or
without separation of sample will be
analysed.
• Inorganic and organic sample can be
analysed.
• Small amount of sample can be analysed.
