AATCC Test Method 149-2012
Chelating Agents:  Chelation Value of Aminopolycarboxylic Acids and Their Salts; Calcium Oxalate Method


Developed in 1975 by AATCC Committee RA90

1.  Purpose and Scope

1.1  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.

2.  Principle

2.1  The chelation value is determined experimentally by titrating a weighed sample of chelating agent with a calcium ion solution of known concentration.  A precipitating anion (oxalate) is present during the titration.  As the calcium solution is added, the ions are chelated by the chelating agent and no permanent precipitate is formed as long as there is free chelating agent present.  Beyond this point, any excess calcium ion that is added reacts with oxalate anion to form a cloudy precipitate which is the endpoint.  The calcium chelation value (CaCV) indicates the amount of calcium ( as calcium carbonate) which will be sequestered by a known weight of chelating and is expressed as milligrams of calcium carbonate (CaCO3) per gram of chelating agent (mg calcium carbonate/g chelating agent).

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