By Sunil Bhardwaj

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If in a titration current is measured as a function of volume of titratnt, to determine the end point. The titration is known as Amperometric titration. The graph of current Vs volume of titrant added is plotted and from the graph endpoint is calculated.

Advantages:

1. The amperometric method is more accurate and sensitive as compared to polarography.

2. As the current obtained in the case of amperometric titration is 20 times more than polarography. Therefore small concentration or (traces) of reducible species can be determined accurately.

3. Several non reducible substances like Mg+2, PO4-3, SO4-2. etc can be determined by titrating them with reducible titrant eg. Mg+2 is titrated against the reducible oxine reagent which gives a diffusion current.

4. Precipitation titrations can be carried out using amperometric method.

5. The apparatus used is simple and easy to set up.

Disadvantages:

1. The major disadvantage of the amperometric method is that sometimes co-precipitation gives inaccurate results.

2. The titration cannot be carried out at potentials more negative than -2 volt because hydrogen will be evolved.

3. More time is required to remove dissolved oxygen.

Applications:

1. The method is specially used for precipitation titration. The following are the some of the examples of the precipitation titrations which can be accurately performed.
Pb+2 Vs K2SO4 OR K2Cr2O4
Ba+2 Vs K2Cr2O4
Mg+2 Vs 8 hydroxy quinoline
Ni+2 Vs Dimethyl glyoxime
Cu+2 Vs Cupferon.

2. The technique is used for redox titrations: In redox titrations there are two oxidation reduction systems. Each is having its own oxidised and reduced state. Thus there are four substances present in the solution whose polarographic behaviour has to be considered eg. Titration of Fe+3 Vs V+2 (vanadous) to give (ferrous ions) Fe+2 and (vanadic) V+3 $$ { Fe }^{ 3+ }+{ V }^{ 2+ }\longrightarrow { Fe }^{ 2+ }+{ V }^{ 3+ } $$ It is found that upto the equivalence point, the diffusion current is proportional to concentration of ferric ions present in the solution. After that more or less it remain constant.

3. Complex formation: The reducible metal ions concentration decreases during the complex formation but the complex ion formed is not reducible. Hence we get a curve in which diffusion current decreases till the end point i.e. when complexation is complete. Further addition of complexing agent has no effect on diffusion current i.e. diffusion current is constant. Cu-EDTA complex ion is not reducible. $$ { Cu }^{ 2+ }+Na-EDTA\longrightarrow Cu-EDTA+2{ Na }^{ + } $$ 4. Rotating platinum micro electrode are used as micro-detectors in liquid chromatography to monitor elution of reducible substances.

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