Hydrolysis information is critical before embarking on any kind of partitioning analysis. Hydrolysis is defined as a reaction of a test substance RX with water, with the net exchange of the group X with OH at the reaction centre. Where this occurs irreversibly, there will be a net disappearance of the substance RX with time, thus confounding any measurement of partitioning behaviour of the substance RX. An alternative form of hydrolysis can result in the incorporation of both the H and OH moieties into a single product.
There are a number of recognised methods for the measurement of hydrolysis at a fixed temperature. The available methods are effectively identical and are thus equally applicable. The principal protocols are given in the guidelines: OECD 111 – Hydrolysis as a function of pH, OPPTS 835.2120 – Hydrolysis and OPPTS 835.2130 – Hydrolysis as a function of pH and temperature.
The existing standard methods are recommended as being sufficiently appropriate for the characterisation of hydrolysis rates for ERA when needed. Details and references are provided in Appendix D.