Demasking

In resolving complex metal-ion mixtures, more than one masking or demasking process may be utilized with various aliquots of the sample solution, or applied simultaneously or stepwise with a single aliquot. In favorable cases, even four or five metals can be determined in a mixture by the application of direct and indirect masking processes. Of course, not all components of the mixture need be determined by chelometric titrations. For example, redox titrimetry may be applied to the determination of one or more of the metals present. 

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 ... 

Demasking methods for a number of masking agents are enumerated in Table 11.38. 

Complexing agent Ion demasked Demasking agent Application... 

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

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 ... 

DETERMINATION OF MAGNESIUM. MANGANESE AND ZINC IN A MIXTURE USE OF FLUORIDE ION AS A DEMASKING AGENT... 

Discussion. In mixtures of magnesium and manganese the sum of both ion concentrations may be determined by direct EDTA titration. Fluoride ion will demask magnesium selectively from its EDTA complex, and if excess of a standard solution of manganese ion is also added, the following reaction occurs at room temperature ... 

Daniell cell 64 d.c. arc source 763, 771 Dead-stop end points 635 Decantation 119 Decomposition potential 504 Degreasing agent 80 Delves cup 788 Demasking agents 312, 334 Densitometers 231, 232 Depolariser anodic, 515 cathodic, 509... 

Vol. 32 Determination of Organic Compounds Methods and Procedures. By Frederick T. Weiss Vol. 33 Masking and Demasking of Chemical Reactions. By D. D. Perrin... 

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