OECD 112 – Dissociation Constants in Water
OECD 112 assesses the dissociation of a chemical in water.
The OECD 112 analysis is important in assessing a materials impact on the environment. In part, because the dissociation constant governs the form of the substance, which then determines its behavior and transport.
Dissociation is the reversible splitting into two or more chemical species. Typically, the dissociation constant measures the tendency of a larger object to separate (dissociate) reversibly into smaller components. The dissociation constant can affect the adsorption of a chemical on soils and sediments and adsorption into biological cells.
OECD 112 determines the dissociation constant by measurements of the concentrations of the dissociated and undissociated forms of the chemical substance. There are two basic approaches for the determination of the dissociation constant:
- titrating a known amount of substance with standard acid or base, as appropriate.
- determining the relative concentrations of the ionized and unionized forms and their pH dependence.
OECD 112 and EPA 830.7370 are commonly performed to determine a chemical’s dissociation constant in water. Customers trying to meet the EPA requirements for pesticide registration or reregistration commonly request this type of testing. The EPA outlines requirements for pesticide registration in 40 CFR Part 158, Data Requirements for Pesticides. Customers also commonly request Biodegradability & Toxicity testing when determining a material’s impact on the environment and to meet regulatory requirements for registration.