electroanalytical techniques

8/4/2019 Electroanalytical Techniques

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I. UNIT II ELECTROANALYTICAL TECHNIQUES

Summary of the learning activity

At the End of this unit the student willbe able to:

Recall the theory on which potentiometry is based

Explain the application of potentiometry to pH measurement, ion selective

electrode and automatic titration stations

Recall the theory of Voltammetry

Interpret Voltammetric data

quantitatively and qualitatively

Explain the concept of on which

polarographic analysis is based

Interpret polarographic data to identify and quantify chemical Species

List of REQUIRED readings

http://en.wikipedia.org/wiki/Electroanalytical_methods

http://www.chem.vt.edu/chem-ed/echem/electroc.html

http://www.chem.vt.edu/chem-ed/echem/potentio.html

http://electrochem.cwru.edu/ed/encycl/art-a03-analytical.htm

http://ull.chemistry.uakron.edu/analytical/Voltammetry/

http://ull.chemistry.uakron.edu/analytical/index.html


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List of relevant useful links

Detailed Description of the activity

Potentiometry

Potentiometry involves measuring activities or concentrations of materials by measuring

potential differences between a measuring (indicator) electrode and a reference

electrode in an electrochemical cell.

VOLTAMMETY

Introduction to Voltammetry

Voltammetry is concerned with application of voltage current time relations during

electrolysis in a cell which has two electrodes one of electrodes is extremely small

called a micro electrode and the large one is called the counter electrode.

The micro electrode is usually polarized i.e. the concentration of the ions at the surface

electrode is different from the concentration of the ions from the bulk of the solution.

Therefore the diffusion of the ions from the bulk of the solution to the micro electrode

becomes an important phenomenon. The total current I= Im+ Id

Im=Migration current

Id=diffusion current

In order to maintain a constant migration current another electrolyte is added to the

solution of the electrolyte this second electrolyte is called a supporting electrolyte.

Usually KCl is used this provides the migration current.


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With the excess of the supporting electrolyte the electro active material will reach the

DME by diffusion. As the voltage at the DME is increased this diffusion current

increases until it reaches a limiting value Id

From theory

D is a constant from diffusion theory, n is the number of electrons involved in the

electrochemical reaction, m is the mass of mercury drops, t is the interval between

mercury drops

It can clearly be seen that the diffusion current is proportional to the concentration of the

electro active analyte.

On application of an increasing voltage to the DME the current changes as shown in the

diagram initially there will be only the residual current which is small and constant. On

increasing the voltage further a point will be reached when the reduction potential of the

analyte is reached and starts to increase with the increasing voltage until the limiting

current Id is reached. E is called the half wave potential and it uniquely identifies the

electro active material in the analyte.

Id

Curr

en

t

VoltageE1/2


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electroanalytical techniques

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