Complexometry

Complexometry is the analytical technique that measures a substance by how much of a complex it forms with a reagent — most famously, the EDTA titration for water hardness and metal ions. The end point is signalled by the formation or disappearance of a coloured complex with an indicator dye. Food laboratories use it for calcium and magnesium in dairy and water, among other metals. It is precise, inexpensive, and well suited to routine control, though masking agents and pH control are needed when several metals compete for the chelating agent.