Masking and demasking agents

TITRATION OF MIXTURES, SELECTIVITY. MASKING AND DEMASKING AGENTS... 

Masking and demasking agents, and (iii) Residual titration methods. 

What are masking and demasking agents with reference to complexometric titrations Give specific examples to justify your statements. 

How Masking and Demasking Agents Can Be Used to Enhance the Selectivity of EDTA Titrations... 

The use of masking and selective demasking agents permits the successive titration of many metals. Thus a solution containing Mg, Zn, and Cu can be titrated as follows ... 

Another type of demasking involves formation of new complexes or other compounds that are more stable than the masked species. For example, boric acid is used to demask fluoride complexes of tin(IV) and molybdenum(VI). Formaldehyde is often used to remove the masking action of cyanide ions by converting the masking agent to a nonreacting species through the reaction ... 

The selectivity of the methods using PAN is enhanced by suitable selection of pH and masking agents. Iron, cobalt, and nickel, for example, react with PAN at pH = 4. At such a low pH the reagent does not form complexes with Mn, Zn and Cd. Cyanide enables manganese to be determined in the presence of Ni, Zn, Cd, Co, and Cu, which form stable cyanide complexes. Zinc and cadmium can be demasked from their cyanide complexes with formaldehyde. 

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