sequestering agent

1. A chemical that forms complexes with metallic ions in solution so that the metallic ions may no longer be precipitated. For example, calcium soap precipitates are not produced from hard water treated with sodium hexametaphosphate. Note however, the tendency for condensed phosphate polymers, such as hexametaphosphates, may be to hydrate in water, especially under conditions of high temperature or high pH, and thereby revert to a simpler and stable phosphate form, such as orthophosphate which can no longer sequester the hardness and metal ions. 2. Any agent that prevents an ion from exhibiting its usual properties because of close combination with an added material. (See chelating agent.)

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