1. Lecture- 22
Subject – Pharmaceutical Analysis-I
Course – B. Pharm 1st Year
Faculty Name – Umesh Kumar
2. CoNtenTs
Titration of mixtures
◦ Masking and Demasking agents.
Estimation of Magnesium
sulphate,
Calcium gluconate
3. Masking and Demasking agents;
Masking agents
One of the important aspect of complexometric titration is its
adoptability in estimation of two or more metals in the same
solution.
This can be done either by selection of suitable pH at which one
metal forms complex without the involvement of other metal ion or
by using a suitable masking agent.
A masking agent is called as auxiliary chelating agent or
complexing agent.
4. Conti……..
Masking agent is a substance that will form complex more strongly
with the metal than the titrant under the conditions of the titration.
Some examples of masking agents and the metals they react with
are triethanolamine for aluminium and iron; thioglycerol for copper;
potassium cyanide for heavy metals; ammonium fluoride for iron
and aluminium etc.
Cyanide ion is one of the effective masking agent to form stable
complexes with Cd, Zn, Hg, Cu, CO, Ni, Ag, Pt. But it does not
mask the alkaline earths, manganese and lead.
5. Demasking agent
It is the substance which releases the masked metal ion.
The cyanide complexes of zinc and cadmium can be demasked by
formaldehyde-acetic acid solution.
Demasking can also be possible by use of chloral hydrate.
Thus, the use of masking and selective demasking agent permits
the estimation of many metals.
