amperometric titration very usefull in analysis

1. Submitted to –
sir Mr. Vijay yadav

2. Definition:
Amperometric titration refers to a
class of titrations in which the equivalence point is
determined through measurement of the electric current
produced by the titration reaction. It is a form
ofquantitative analysis.
Indicator microelectrode: DME
 Reference electrode: SCE

4. Explaination:
Consider a solution containing
the analyte, A, in the presence of some conductive buffer. If
anelectrolytic potential is applied to the solution through a
working electrode, then the measured current depends (in
part) on the concentration of the analyte. Measurement of
this current can be used to determine the concentration of
the analyte directly; this is a form of amperometry.
.
However, the difficulty is that the
measured current depends on several other variables, and it
is not always possible to control all of them adequately.
This limits the precision of direct amperometry.

5. If the potential applied to the working electrode is sufficient
to reduce the analyte , then the concentration of analyte
close to the working electrode will decrease. More of the
analyte will slowlydiffuse into the volume of solution close
to the working electrode, restoring the concentration. If the
potential applied to the working electrode is great enough
(an overpotential), then the concentration of analyte next to
the working electrode will depend entirely on the rate of
diffusion. In such a case, the current is said to be diffusion
limited. As the analyte is reduced at the working electrode,
the concentration of the analyte in the whole solution will
very slowly decrease; this depends on the size of the working
electrode compared to the volume of the solution.

6. What happens if some other
species reacts with the analyte
……????
For instance, chromate ions
can be added to oxidize lead ions. After a small quantity of
the titrant (chromate) is added, the concentration of the
analyte (lead) has decreased due to the reaction with
chromate. The current from the reduction of lead ion at the
working electrode will decrease. The addition is repeated,
and the current decreases again. A plot of the current
against volume of added titrant will be a straight line.
After enough titrant has been
added to react completely with the analyte, the excess titrant
may itself be reduced at the working electrode. Since this is
a different species with different diffusion characteristics
(and different half-reaction), the slope of current versus

7. equivalence point..
C
u
r
r
e
n
t
Equivalence point

8. Advantages:
 The chief advantage over direct amperometry is that the
magnitude of the measured current is of interest only as an
indicator. Thus, factors that are of critical importance to
quantitative amperometry, such as the surface area of the
working electrode, completely disappear from amperometric
titrations.
The chief advantage over other types of titration is the
selectivity offered by the electrode potential, as well as by
the choice of titrant.
 The Patch Amperometry Technique: Design of a Method
to Study Exocytosis of Single Vesicles.

9. Applications:
Amperometric titrations are used for redox;
precipitation;& complexometric titrations of reducible
inorganic or organic ions.For conventional acid-base
titrations it is not useful.
In the determination of moisture by Karl Fisher reagent,
the end point is located by amperometry.