AATCC 149-2018: The active content of ethylenefiaminetetraacetic acid (EDTA), N-hydroxyethylenediaminetriacetic acid (HEDTA) and diethylenetriaminepentaacetic acid (DTPA) and their salts is usually expressed by the calcium chelation value (CaCV). This value indicates the amount of calcium ( as calcium carbonate) which will be chelated by a known weight of chelating agent.