[2] Structurally, it is similar to eriochrome blue black R, which is obtained from calconcarboxylic acid by decarboxylation and reaction with sodium hydroxide.

[2] Calconcarboxlic acid is soluble in water and a variety of other solvents, including sodium hydroxide, ethanol and methanol.

[2] Calconcarboxylic acid was thus adopted as a superior alternative due to its ability to give a good and visual endpoint and its rapid performance even with the presence of magnesium.

Free calconcarboxylic acid is blue colour, but changes to pink/red when it forms a complex with calcium ions.

The accuracy of this method may also be affected by the presence of metal ions such as copper, iron, cobalt, zinc or manganese in sufficiently high concentrations.