Polarography is an electroanalytical technique invented in 1922 by Jaroslav Heyrovsky for which he won the Nobel Prize. It involves measuring the current in a solution under an applied potential using a dropping mercury electrode and a reference electrode such as SCE. Mercury is used as the working electrode due to its wide negative potential range and ability to regenerate its surface. A polarogram is generated by plotting current versus applied potential, showing residual, diffusion, and limiting currents. Polarography can be used for qualitative and quantitative analysis of metals, drugs, and other compounds.

1. SAMRAT PRITHVIRAJ CHAUHAN GOVERNMENT COLLEGE
AJMER
2020-2021
Polarography
Submitted By
Pooja Rawat
M.Sc. Chemistry
Semester 2nd
Department of chemistry
Principle and Instrumentation

2. Table Of Content
 History
 Introduction
 Principle of Polarography
 Polarized and Depolarized Electrode
 Why Mercury?
 Examples of Mercury Electrode
 Polarogram
 Instrumentation
 Application of Polarography

3. History
 Polarography was
invented in 1922
by Cezech
chemist Jaroslav
Heyrovsky (the
father of electro
analytical
chemistry) for
which won noble
prize in 1959.

4. Introduction
 Polarography also called Polarographic
analysis or voltammetry in analytic chemistry.
 Polarography is an voltametric technique and
consists in the measurement of applied
potential versus current flow in solutions.
 The data so obtained can thus be interpreted
in terms of the nature and behaviour of many
substances and systems.

5. Principle of Polarography
 Study of solutions of electrode processes by
means of electrolysis with two mercury
electrode, one Polarizable and Non-
polarizable, the former formed by mercury
regularly dropping from capillary tube.
 Polarized electrode- Dropping Mercury
Electrode(DME) .
 Depolarized electrode- Saturated Calomel
Electrode(SCE).

6.  Mercury continuously drops from reservoir
through capillary tube into the solutions.
 The optimum interval between drops for most
analysis is between 2 to 5 seconds.

7. Polarized And Depolarized
Electrode
 If the electrode potential
has great changes when
infinite small current flow
through the electrode,
such electrode is referred
as polarized electrode.
Example- DME.
 If the electrode potential
does not change with
current, such electrode is
called depolarized
electrode . Example-
SCE.

8. Why Mercury?
 Mercury as working
electrode is useful
because
1) It displays a wide
negative potential
range.
2) Its surface is
readily
regenerated by
producing a new
drop of film.
3) Many metals ions
can be reversibly
reduced into it.

9. Examples Of Mercury Electrodes
 In Polarography, mercury is used as a working
electrode, mercury it is a liquid. The working
electrode is often a drop suspended from the
end of a capillary tube.
 Examples:
 HMDE (Hanging mercury drop electrode)
 DME (Dropping mercury electrode)
 SMDE (Static mercury drop electrode)

11. Polarogram
 It is a graph of current versus potential in
Polarographic analysis.
Current applied voltage curve(Polarogram)
A
B
C
D

12. Types of current
1) Residual Current(iR)– The current which is
associated with the impurities is known as residual
current. AB portion of the graph corresponds to
residual current..
2) Diffusion Current(id) – At the point B, the potential
applied is equal to reduction potential of metal ion.
The metals gets reduced over DME and current is
produced. As large amount of metal ions are
reduced current will increase rapidly. At the point C
reduction is complete.
3) Limiting Current(iL)- At the point C, all the metallic
ions are reduced as no more metallic ions, so no
further increase of current remain constant. This
constant current is known as Limiting Current.

13. Ilkovic Equation
 Diffusion current calculated by following equation known as
Ilkovic Equation.
 The equation is named after the scientist who derived it, the
Slovak Chemist, Dionyz Ilkovic(1907-1980)

14. Instrumentation
 The basic component of the
experimental setup are the
polarographic cell and the DME.
 The polarographic cell is a H
shaped vessel. The two tubes
are connected through an agar
agar salt bridge and a sintered
glass tube.
 One half of the cell act as anode
which is usually a reference
electrode such as saturated
calomel electrode (SCE).
 The other half cell contains the
solution of the sample analyte
and the DME as the cathode

15.  The DME consists of a 5-20 cm long capillary tube
with an inner diameter 0.06-0.08mm through which
mercury is forced under pressure exerted by
approximately 50 cm column or mercury connected to
a mercury reservoir.
 The electrical circuit consists of a DC source,
potentiometer, a voltmeter and micrometer us usually
a galvanometer.
 The DME is connected to the negative terminal while
SCE is connected to the positive terminal of DC
source.
 Using the potentiometer an emf upto 3 volt may be
gradually applied to the cell.
 Since the DME is connected to the negative terminal
DC source the applied voltage is given a negative sign

16. Application of polarography
 1. Qualitative analysis: It helps in characterization of organic matter
and various metal interactions from half wave potential of the
current v/s voltage graph.
 2. Qualitative analysis: Polarography is used in the determination of
concentration of drugs, metal ions etc. in the given sample.
 3. Determination of inorganic compounds: Polarography is used in
determination of cations and anions in the presence of interfering
ions.
 4. Determination of organic compounds: Polarography is used in
determination of structure, quantitative analysis of mixture of
organic compounds.
 5. Estimation of dissolved oxygen: Amount of oxygen dissolved in
aqueous solution or organic solvent can be calculated with the help
of Polarography.
 6. Pharmaceutical applications: Tetracycline antibiotics,
sulphonamides can be analysed by Polarography.

17. Reference
 Advanced Physical Chemistry
by Dr.J.N.Gurtu and A.Gurtu
 Basic concepts of analytical chemistry
by S.M.Khopkar

http://www.searchmap.eu/blog/jaroslav:heyrovsk
y/

18. Thanks You