Amperometry is a type of voltammetric analysis that measures current over time while maintaining a constant potential at the working electrode. It can determine both the total elemental content and nature of dissolved species. A typical setup involves a working, reference, and auxiliary electrode in a measuring chamber. Current is measured as a function of the applied potential to generate a voltammogram. Amperometric titrations use this principle to locate the equivalence point from the intersection of current vs volume curves before and after the endpoint. Amperometry has advantages over other methods as it can analyze very dilute solutions and is unaffected by soluble or hydrolyzing products near the endpoint.

1. Amperometry
Principle :
Amperometry analysis is a type of
voltammetric analysis which is widely used
in food processing industries.

2. Typical cell arrangement for amperometric titrations with a rotating platinum disk electrode.
Amperometry:
A form of voltammetry in which we measure current as a function of time
while maintaining a constant potential to the working electrode

3. Amperometry
Amperometry is extended technique of D.C. polarography.
• Well suited for trace level determination of metal ions.
• One of the most distinguishing feature of this technique is that
like other voltammetric techniques, it can also indicate the nature
of the species dissolved in the solution
• Does not merely limit itself to the total elemental content as is
the case with sophisticated non-electrochemical methods such as
neutron activation analysis, X-ray fluorescence and atomic
absorption spectroscopy

5. A voltammetric analyses is done by using a certain setup of a measuring chamber
which contains three electrodes.
Working electrode (microelectrode)
Reference electrode
Auxiliary electrode
Apart from these electrodes, there is a voltage source and a devices for measuring
current and voltage – voltmeters and ammeter.
1. The method is based on the principle that the measurements of changes in time (τ) in
the current (I) flowing through the system of electrodes in relation to potential (E)
applied to the working electrode.
2. The change registered in the current allow drawing the I(τ) = f[E(τ)] relationship
which is known the voltammogram.
3. If the same measurements of the current are carried out at constant potential, then it
becomes a classical amperometric system.
4. Amperometric measurements completed in stirred solution or with rotating electrode
which is also termed as hydrodynamic amperometry.
5. The best use of Amperometry apparatus is to detected dissolved oxygen which is
reduced at the measuring electrode.
6. By using a micro- potentiotat the potential of the measuring electrode is kept at a
constant which is main characteristic for the oxygen reduction in Amperometry
technique.
7. Hence, the diffusion limited current is directly proportional to the oxygen
concentration.

6. Amperometric Titration

7. DIFFERENT ELECTRODES USED IN
AMPEROMETRY
• Though the traditional D.C. amperometric titrations are performed
with D.M.E. as the indicator electrode
• Other electrodes have also been used for the purpose like Platinum
wire electrode, rotated at constant speed of 600 r.p.m. or more, has
been used on a large scale. [Latinen and Kolthoff, 1941] .
• Mechanical mixing help in bringing the electroactive species to the
electrode surface, besides diffusion.
• Consequently, limiting currents are much higher, about twenty
times, in comparison to those obtained with D.M.E.

8. Limitations of RPE
• Limiting currents are not very reproducible and often influenced
by the previous history of the electrode.
• High currents obtained with the electrode, make it particularly
sensitive to traces of oxygen in the solution.
• Hydrogen over-voltage for this electrode is low and greatly
restricts the range of potentials for study. In fact, potentials more
negative than -1.00V (Vs S.C.E.) cannot be applied even in almost
neutral solutions.

9. Other Electrodes
• Vibrating platinum electrode [by Harris and Lindsey, 1948] .
• Rotating microelectrode of gold, graphite and aluminium, tantalum
and certain other material have also been used at times.
• Stationary glassy carbon disc electrode has also found application.
• However, all these solid electrodes suffer from one or the other
serious drawback.
• In amperometric titrations DME is used as an indicator electrode.

10. Advantages of Amperometric titration
1. In amperometry titration, a few current measurements at constant
applied voltage before and after the end point are sufficient to
estimate the equivalence point and end point.
2. Amperometry titration is useful for such case in which the
potentiometric, precipitation titration or in acid-base titration are
unsatisfactory.
3. A amperometric titration can be carried out at low dilutions also at
which many other titration are no longer yield accurate results.
4. 'Foreign' salts do not create any interference in amprometric
titration. They are usually added as the supporting electrolyte for the
elimination of the migration current.
5. No change in temperature is observed during titration and this
titration is independent of the characteristics of the capillary.

11. ADVANTAGES OF DROPPING MERCURY ELECTRODE
Some advantages of dropping mercury electrode are as under:
1. No chance of poisoning, as fresh electrode is formed after approx every three seconds.
2. Each drop behave exactly in the same way as the preceding one and the average current
measured with the galvanometer is accurately reproducible from drop to drop for a given
applied potential.
3. Mercury is noble metal so there is no reaction with constituent of electrolytic solution.
4. It adopts to the applied potential instantaneously so is ideally polarisable.
5. A jerk or shock that causes one drop to behave erratically does not affect the following
one; the DME is thus much less sensitive to mechanical disturbance than is a stationary
microelectrode.
6. Dropping mercury electrode (DME) has small dimension hence electrolysis is possible in
small volume of the solution and very small number of cations reduced or anions oxidized in
electrolysis, so that same solution can be used for hours, even days.
7. With mercury electrode, it is possible to reach more negative potential in comparison to
any metal electrode, before evolution of hydrogen begins. Consequently, a large number of
reactions can be studied.

12. AMPEROMETRIC TITRATIONS WITH TWO INDICATOR ELECTRODES
• Two identical stationary microelectrodes can also be used to
perform titrations by following current as a function of volume of
titrant.
• The technique is sometimes referred to as “dead-stop end point
technique”, as the current at the end point is zero or near zero.
• History of these biamperometric titrations begins with the work of
Foulk and Bawden.
• Biamperometric titration technique is also quite simple, sensitive,
rapid and accurate like amperometry.
• However, it lacks the universal applicability of amperometric
titrations and its use has remained largely restricted to redox
systems and certain precipitation reactions.

13. MERITS AND DEMERITS OF
AMPEROMETRY
1. Amperometric titrations have a wide field of applicability and
different types of amperometric titrations can be accomplished
successfully e.g.
a) Precipitation titrations
b) Acid base titrations
• This is because the readings near the equivalence point have no
special significance
• Slight soluble reaction can also be determined.
• Readings are recorded in the region of excess titrant or excess
reagent where solubility or hydrolysis is suppressed by the mass
action effect.
• The point of intersection of two lines gives equivalence point.

14. MERITS AND DEMERITS OF AMPEROMETRY
• It is highly sensitive technique and used for very dilute solution upto ppm level.
• The titration can usually be carried out rapidly since the end point is found graphically.
• This technique requires simple manual assembly and no prior calibration. Recording of
whole polarogram is not necessary.
• It does not require determination of capillary characteristics and also the temperature
need not to be adjusted or known as long as it is kept constant. Additionally:
a) Relatively high solubility of the product
b) Low stability of the complex or
c) A slow reaction in the vicinity of equivalence point do not affect the accuracy of
estimations as the null point is obtained from the limiting current vs. volume and the
measurements of current near this point are of little significance in locating it just as in
other electrometric titrations.
• All the titrations can often be carried out under conditions where visual or
potentiometric methods are not possible and it is unimportant whether the electrode
reaction is reversible or not.
• These titrations have also been used to study co-precipitation, adsorption and to
determine solubility product and stoichiometry .
6. Foreign salts may frequently be present without any interference and indeed they are
added as the supporting electrolyte in order to eliminate the migration current.

15. Typical amperometric titration curves:
(left) analyte is reduced, reagent is not
(center) reagent is reduced, analyte is not
(right) both reagent and analyte are reduced.