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Dissociation Constant Kd

By Little Pro on 2016-01-13 Views:  Update:2017-01-18

Dissociation constant (Kd) is a mathematical constant that describes the tendency of a large molecule to dissociate reversibly into smaller components. For an acid, this dissociation constant is called Ka. You may find it in the section 9 of a safety data sheet (SDS).

Regulatory Implications of Dissociation Constant

Substances with larger dissociation constants usually have bigger water solubility. They are less likely to enter air through vaporization. The toxicological effects of small components formed by dissociations shall be considered before conducting toxicology studies.

Under REACH, the study does not need to be conducted if:

  • the substance is hydrolytically unstable (half-life less than 12 hours) or is readily oxidisable in water, or
  • it is scientifically not possible to perform the test for instance if the analytical method is not sensitive enough.

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