AMPEROMETRY TITRATION PRINCIPLE,INSTRUMENTATION and MULTIPLE CHOICE QUESTIONS

PRINCIPLE:-

It is based on the principle of polarography , with the exception that the voltage is maintained constant during the titration.

Diffusion current ∝ concentration of electroredusible ion

Potential applied between polarizable & non polarizable is kept constant.

INSTRUMENTATION:-

Dropping Mercury Electrode :-

• Capillary diameter is 20-50μm
• Droplet timings 2-12 sec/drop, so 5-30 drops/min is possible
• potential range +0.4v to -0.18v

Advantage :-

Always new surface

Disadvantage :-

• Capillary may blocked due to dust particles or it may break.
• Applicable only to +0.4 to -1.8v range.

Mercury Pool :-

High surface area & acts as anode.

Methodology :-

• Potential of the instruments is selected & fixed.
• Take the sample solution & add supporting electrolyte.
• Titrant is added and current flow is measured in mA.
• CONC. upto 10¯⁴molar can be determined.

TYPES OF AMPEROMETRY TITRATION:-

1. Titration of electro-reducible Vs electro non-reducible
2. Titration of electro non-reducible Vs electro-reducible
3. Titration of electro-reducible Vs Titration of electro-reducible
4. Titration of electro non-reducible Vs Titration of electro non-reducible

APPLICATION:-

1. Determination of water by using karl-fisher reagent.
2. Use as amperometric detector in HPLC (ng/ml to pg/ml)
3. Quantification of ions / mixture of ions.
4. List of organic & inorganic compound assed by amperometric titration.

• ORGANIC:- Sulpha drug, vitamin C , Phenobarbitone
• INORGANIC:- Halides,Oxalate,Zn ions , Pb ion etc.

MCQ 

1. which is working principle of amperometry ?

a.It is based on the principle of polarography , with the exception that the voltage is altered during the titration.

b.It is based on the principle of polarography , with the exception that the current is maintained constant during the titration.

c.It is based on the principle of polarography , with the exception that the voltage is maintained constant during the titration.

d.It is based on the principle of polarography , with the exception that the current is maintained altered during the titration.

2.What is the diameter DEM ?

a.10-30μm

b.20-50μm

c.0-5μm

d.20-30μm

3. Which sentence is false about DEM ?

a.potential range -0.4v to +0.18v

b.5-30 drops/min is possible

c.Capillary diameter is 20-50μm

d.potential range +0.4v to -0.18v

4.Which is not applicable for amperometry ?

a. Identification of polysaccharide

b.Quantification of ions / mixture of ions

c.Use as amperometric detector in HPLC (ng/ml to pg/ml)

d.Determination of water by using karl-fisher reagent

ANSWER KEY:-

1.C

2.B

3.A

4.A

REFERENCE:-

TEXT BOOK OF PHARMACEUTICAL ANALYSIS OF THIRD EDITION OF DR.S.RAVI SANKAR (12.1-12.7)