instrumentation slides

1. POLARGRAPY
Presented To: Dr. Abbas
Presented By: Shabnam Faiz
R.No: 06

2. POLARGRAPY
INTRODUCTION
Polarographic Analysis:
• Is a method of analysis based on the measurement of current electrolysis
of an electroactive species at a given electrode potential under controlled
conditions.
• It is the branch of voltammetry where the working electrode is a dropping
mercury electrode (DME) or a static mercury drop electrode (SMDE),
which useful for their wide cathodic ranges and renewable surfaces.

3. POLAROGRAPHY
• In 1922, Polarography was developed by (zech chemist, Jaroslav
Heyrovsky, who won the noble prize for his discovery.
• An electromechanical techniques of analysing solutions that measure the
current flowing between two electrodes in the solution as well as gradually
increasing applied voltage to determine respectively the concentration of a
solute and its nature.

4. POLAROGRAPHIC ANALYSIS
• Is a method of analysis in which the solution to be analysed is electrolysed
in such a way that the graph of current against voltage shows what is in
solution and how much is present.
• In this method, a reference electrode and an indicator electrode are
required.

5. POLAROGRAPHIC ANALYSIS
• Reference electrode: acts to maintain a constant potential throught the
measurement.
• Indicator electrode: acts to maintain a constant potential impressed upon
it from a external source.

6. POLAROGRAPHIC ANALYSIS
• Diagram

7. POLAROGRAPHIC ANALYSIS
EXAMPLES OF MERCURY ELECTRODES:
• In polarography, mercury is used as a working electrode, because mercury
it is a liquid.The working electrode is often a drop suspended from of a
capillary tube.
Examples Of Electrodes:
HMDE (HANGING MERCURY DROP ELECTRODE)
• We extrude the drop of Hg by rotating a micrometer screw that pushes the
mercury from a reservoir through a narrow capillary.

8. POLAROGRAPHIC ANALYSIS
 DME (DROPING MER CURY ELECTRODE):
• Mercury drops at the end of the capillary tube as a result of gravity. Unlike
the HMDE, the mercury drop of a DME grows continuously as mercury
flows from the reservoir under the influence of gravity and has a infinite
of several seconds.
• At the end of its lifetime the mercury drop dislodged ,either manually or
its own. and replaced by new drop.

9. POLAROGRAPHIC ANALYSIS
DSME (STATIC MERCURY DROP ELECTRODE):
• Uses a solenold driven plunger to control the flow of mercury.
• Activation of the solenold mometerily lifts the plumber, allowing mercury
to flow through the capillary and forming a single, hanging Hg drop

10. ADVANTAGES OF DME
• Surface area is reproducible
• Constant renewal of electrode surface eliminating poisoning effect
• Mercury forms amalgams with most metal ions and alkali metal ions
which are reducible
• It is useful over the range of +0.4 to -1.8V

11. ADVANTAGES OF DME
• Electrodes cannot be used above +0.4V
• Capillary is difficult to maintain sice dust or either particularly matter can
be block the capillary
• Mercury can be easily oxidixied thus limit the feasible range of the
electrode.

12. PRINCIPLE
• Study of solutions or of electrode processes by means of electrolysis with
two electrodes one polarizable, the former formed by mercury regularly
dropping from capillary tube.
POLARIZED ELECTRODE: Dropping Mercury Electrode (DME)
DEPOLARIZED ELECTRODE: Saturated Calomel Electrode

13. POLAROGRAPHIC ANALYSIS
• Mercury continously drops from reservoir through a capillary tube into
nthe solution.
• The optimum interval between drops for most analysis is between 2 and 5
seconds.

14. WORKING (INSTRUMENT DIAG)
• It consist of polarsable elctrode (DME) and non polarsible electrode
(saturated calomel electrode)
• Between these electrodes, the required potential range (0 to -3v) can be
applied
• It consist of sample cell in which the sample solution to be analysied tis
kept

15. WORKING (INSTRUMENT DIAG)
• Sample cell made up of glass and has tampering edge to hold at the bottom
to hold mercury - after the droplets have been formed
• The capillary is dipped into the solution to be analysed and the height of
mercury reservoir is analysied in such a way drop time of about 2-7 sec is
set
• Supporting electrolite be like kcl (50-100 times sample conc) is added to
the sample solution to eliminate migration current.

16. WORKING (INSTRUMENT DIAG)
• In polarographic analysis" diffusion which is proportional to the conc of
the electrolite and hence only the diffusion current has to be measured
• In normal condition, without the supporting electrolyte, migration current
is also recorded which is not required
• Oxygen present in sample solution is removed by passing nitrogen or
using alkaline pyrogallol solution. Maximum suppressors are added in the
req conc.

17. POLAROGRAPHIC ANALYSIS
• When all these things are done, initial and final potential is set in the
instrument the current voltage cure is recorded
• From the current voltage curve, half wave potential & diffusion current is
determined and thus qualitative and quantitative analysis is performed

18. POLAROGRAPHIC DATA
• Obtained from an automatic recording instrument is called a polarogram, and the
trace a polarographic ware.
POLAROGRAM: It is a graph of current versus potential in a polarographic
analysis.
3 CATEGORIES:
A. Collectively referred to as residual current
B. Referred to as diffusion current resulting from the reduction of the sample
C. Called the limiting current

19. POLAROGRAPHIC DATA
• The diffusion current of a known concentration of reference standard are
first determined followed by the determination of the determination of the
diffusion current of the unknown concentration.

20. POLAROGRAM
• (Residual current) which is the current obtained when no electrochemical
change takes place.
• (Average current/limiting current) is the current obtained by average
current values throuhtout the life time of the drop while
• (Diffusion current) which is the current resulting from the diffusion of
electroactive species to the drop surface.

21. POLAROGRAPHIC ANALYSIS
RESIDUAL CURRENT:
• It is the sum of the relativity larger condens current (charging current) and
a very small faradic current.
MIGRATION CURRENT:
• It is due to migration of cations from the bulk of the solution towards
cathode due to diffusive force. Irrespective of concentration gradient.

22. POLAROGRAPHIC ANALYSIS
DIFFUSION CURRENT:
• Diffusion current is due to the actual diffusion of electroreducible ion from
the bulk of the sample to the surface of the mercury droplets due to
concentration gradient.
LIMITING CURRENT:
• Beyond a certain potential, the current reach a steady value called as the
limiting current.

23. POLAROGRAPHIC ANALYSIS
Factors Affecting Diffusion Current:
CONCENTRATION: Diffusion current is directly proportional to
concentration of the electroreducible ions. This forms the basis
quantitative analysis. i.e, if concentration is less, then diffusion current is
less. If concentration is more then diffusion current also more.

24. POLAROGRAPHIC ANALYSIS
TEMPERATURE:
• Diffusion of ions is being affected by temperature hence diffusion current
also varies with respect is temperature (directly proportional).

25. POLAROGRAPHIC ANALYSIS
ILKOVIC EQUVATION:
• Id = 708 n C D 1/2 m 2/3 t ¹/6
• Id = diffusion current due to electro reducible ions.
• n=no of electrons involved in the reduction of one molecule.
• C =conc. Expressed in mmol/lit
• D = wt .of mercury flowing through capillary
• i = drop time in seconds.

26. QUALITATIVE ANALYSIS
• Direct comparison method.
• CCM- calibration curve method.
• Internal standard or pilot ion.
• Method of standard addition.

27. INORGANIC ANALYSIS
• Composition of alloy.
• Purity of element.Analysis of trace trace elements like copper, Zn, iron,
nickle, lead, manganese.
• Trace metals and metal containing drugs.
• Blood and serum cancer diagnosis.

28. APPLICATIONS:
• Applications of polarography are limited to those species both organic and
inorganic that can be oxidized or reduced at electrode.
• The majority of the chemical elements can be identified by polarographic
analysis, and the method is also applicable to the analysis of alloys and
various inorganic compounds.

29. APPLICATIONS:
• In addition, polarography is useful in identifying numerous types of organic
compounds and in the study of chemical equilibria and the rates of reactions
in solutions.
• The measurement of polarographic current provides a simple method for
the estimation of the rate of several fast electrode reactions.

30. APPLICATIONS:
• The technique has contributed substantially to the study of adsorption of
several surface-active molecules on a mercury surface.
• Polarography is used predominantly for trace metal analysis of alloys, ultra-
pure metals, minerals, environmental analysis (air, water, soil and sea water
contaminants), foodstuffs, beverages and body-fluids, toxicology and clinical
analysis.

31. APPLICATIONS:
• It is also useful in the:
• analysis of biological systems to determine vitamins, alkaloids, hormones,
terpenoid substances and natural colouring substance,
• analysis of drugs and pharmaceutical preparations,
• determination of pesticide or herbicide residues in foods,
• structure determination of many organic compounds etc.

32. APPLICATIONS:
• Polar graphic analysis of organic compounds
• This technique is used in organic chemistry for qualitative and quantitative
analysis and structure determinations.
• Most of the organic compounds are insoluble in pure aqueous medium and
also in mercury to form amalgam.
• Therefore, the solvent in which the organic compound and its electrode
product is soluble is added to the supporting electrolyte.

33. APPLICATIONS:
• These solvents include various alcohols or ketones, dimethyl formamide,
acetonitrile, ethylene diamine and others.

34. THE END