Masking and demasking reagents in Complexometric titration
Masking and demasking reagents are used in complexometric titrations to selectively mask or demask interfering ions that may interfere with the determination of the metal ion of interest. Masking agents are used to prevent the interference of unwanted metal ions, while demasking agents are used to remove the masking agent from the metal ion of interest.
Masking agents are typically chelating agents that can form complexes with the interfering metal ions. The complex formed between the masking agent and the interfering metal ion is usually more stable than the complex formed between the metal ion of interest and the chelating agent. This prevents the interfering metal ions from interfering with the determination of the metal ion of interest.
Common masking agents include ethylenediaminetetraacetic acid (EDTA) and its salts, which are used to mask calcium, magnesium, and other metal ions. Other masking agents include citric acid, tartaric acid, and oxalic acid.
Demasking agents are used to remove the masking agent from the metal ion of interest, allowing the metal ion to be titrated with the chelating agent. Demasking agents typically form a more stable complex with the masking agent than the metal ion of interest, causing the masking agent to be displaced from the metal ion of interest.
Common demasking agents include sodium cyanide, which is used to demask copper from EDTA complexes, and potassium iodide, which is used to demask mercury from EDTA complexes.
It is important to carefully select the appropriate masking or demasking agent for the metal ion being titrated and to ensure that the concentration of the masking or demasking agent is carefully controlled to prevent any unwanted effects on the titration.
Overall, the use of masking and demasking agents in complexometric titrations can help to improve the accuracy and reliability of the titration, particularly in samples containing multiple metal ions. However, it is important to carefully consider the potential effects of the masking or demasking agent on the titration and to select appropriate concentrations to prevent any unwanted effects.
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