Masking agent

Tabie 11.37 Masking Agents for Anions and Neutrai Moiecuies 11.100... 

Probably the most extensively applied masking agent is cyanide ion. In alkaline solution, cyanide forms strong cyano complexes with the following ions and masks their action toward EDTA Ag, Cd, Co(ll), Cu(ll), Fe(ll), Hg(ll), Ni, Pd(ll), Pt(ll), Tl(lll), and Zn. The alkaline earths, Mn(ll), Pb, and the rare earths are virtually unaffected hence, these latter ions may be titrated with EDTA with the former ions masked by cyanide. Iron(lll) is also masked by cyanide. However, as the hexacy-anoferrate(lll) ion oxidizes many indicators, ascorbic acid is added to form hexacyanoferrate(ll) ion. Moreover, since the addition of cyanide to an acidic solution results in the formation of deadly... 

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. 

TABLE 11.36 Masking Agents for Various Elements Continued)... 

A pseudo-separation method in which a species is prevented from participating in a chemical reaction by binding it with a masking agent in an unreactive complex. 

Suggest a masking agent for the analysis of Al in the presence of Fe. Repeat for the analysis of Fe when Al is an interferent. 

To find a suitable masking agent, we look for a species that binds with the interferent but does not bind with the analyte. Oxalate, for example, is an inappropriate choice because it binds with both Al and Fe. From Table 7.6 we find that thioglycolic acid is a selective masking agent for Fe in the presence of Al and that F is a selective masking agent for Al in the presence of Fe. 

As shown in Example 7.13, a masking agent s effectiveness can be judged by considering the equilibrium constants for the analytical and masking reactions. 

Show that CN is an appropriate masking agent for Nb+ in a method in which nickel s complexation with EDTA is an interference. 

Ni(CN)4 is greater than that for the Ni-EDTA complex. In fact, the equilibrium constant for the reaction in which EDTA displaces the masking agent... 

Show that F is an effective masking agent in preventing a reaction of AP+ with EDTA. Assume that the only significant forms of fluoride and EDTA are F and Y. ... 

Cyanide is frequently used as a masking agent for metal ions. The effectiveness of CN as a masking agent is generally better in more basic solutions. Explain the reason for this pH dependency. 

The successful employment of any insecticide depends on its proper formulation into a preparation that can be appHed for insect control with safety to the apphcator, animals, and plants. Insecticides are commonly formulated as dusts, water dispersions, emulsions, and solutions. The preparation and use of such formulations involves accessory agents such as dust carriers, solvents, emulsifiers, wetting and dispersing agents, stickers, and deodorants or masking agents (1). 

Fig. 2. Odor masking (a) how masking agents work, and (b) masking curve for tobacco odor, where ( ) is perceived odor strength (treated) (B) is...

Flavor-Masking Deodorant. In addition to its use as a constituent of perfume compositions, vanillin is also useful as a deodorant to mask the unpleasant odor of many manufactured goods. As a masking agent for numerous types of ill-smelling mass-produced industrial products, particularly those of synthetic mbber, plastics, fiber glass, inks, etc, vanillin finds extensive use. It is often the most inexpensive material for the amount of masking effect it provides. Only traces are required for this purpose as the odor of vanillin is perceptible in dilutions of 2 x 10 mg/m of air. Cmde vanillin is acceptable for such purposes. 

Poisons ndInhibitors. Catalyst poisons and inhibitors can come from the fuel, the lube oil, from engine wear and corrosion products, and from air ingestion. There are two types of catalyst poisons one poisons active sites, the other is a masking agent. 

Masking agent Substance used to cover up or disguise unpleasant odors. Liquid masking agents are dripped into wastewater, sprayed into the air, or evaporated (using heat) with the unpleasant fumes or odors and then discharged into the air by blowers to make an undesirable odor less noticeable. 

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