(American Society for Testing and Materials definition). Complex phosphates are sequestrants, since they have the ability to inactivate the water hardness metals (calcium and magnesium) and iron and manganese without precipitation. Water softening without precipitation, i.e., by sequestration, distinguishes the complex phosphates from compounds such as sodium carbonate and sodium orthophosphate, which soften by precipitation of the hardness metals.
Glossary
Sequestering agent
11.16.21
"Any compound that in aqueous solution combines with a metallic ion to form a water-soluble combination in which the ion is substantially inactive"
