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Choosing the right chelate

Our products can be used directly in chemical processes or formulated as water-soluble products. We can discuss your process to establish which product should be used. The type and quantity of metal ions as well as the anions involved in the process need to be considered.

An important factor is the strength of the complex formed between the metal ion and the chelating agent. This determines whether the complex will be formed in the presence of competing anions. The stability or equilibrium constant (K), expressed as log K, has been determined for many metals and chelating agents. The higher the log K values, the more tightly the metal ion will be bound to the chelating agent and the more likely that the complex will be formed.

Stability constants (Log K values)1

Metal ionEDTAGLDADTPAHEDTANTAEDGPDTA
Al3+16.412.2*18.614.411.47.716.3
Ba2+7.93.58.76.24.83.43.9
Ca2+10.75.910.88.16.44.77.2
Cd2+16.59.1*19.013.79.87.413.8
Co2+16.510.0*18.814.510.48.015.5
Cu2+18.813.121.217.413.011.818.8
Fe2+14.38.7*16.212.28.96.813.4
Fe3+25.111.7*28.019.715.911.621.6
Hg2+21.514.326.420.114.35.519.8
Mg2+8.85.29.37.05.53.46.2
Mn2+13.97.6*15.211.17.55.510.0
Ni2+18.410.9*30.117.111.59.318.2
Pb2+18.010.5*18.815.611.59.413.6
Sr2+8.74.19.86.85.03.85.2
Zn2+16.510.0*18.214.610.78.415.2


1 A.E. Martell, R.M. Smith, NIST Critically selected stability constants of metal
   complexes (NIST Standard reference database 46, version 7.0, 2003)
* As determined by AkzoNobel

Stability constants: as determined at an ionic strength of 0.1M and at a temperature of 25°C, or if not available at 20°C.