Reaction mass of diisobutyl hydrogen phosphate and isobutyl dihydrogen phosphate

Hydrolysis

Description of key information

One reliable key study is available on the registered reaction mass. No hydrolysis of the two main components, the monoester and the diester, was measured at any of the pHs and temperatures tested and therefore the half-life for hydrolysis of the registered reaction mass is assessed to be more than one year.

Key value for chemical safety assessment

Half-life for hydrolysis:

1 yr

at the temperature of:

25 °C

Additional information

One reliable key study is available to assess the hydrolysis potential of the registered reaction mass. This study was performed according to Method C7 Abiotic Degradation, Hydrolysis as a Function of pH and Method 111 of the OECD Guidelines for Testing of Chemicals, with GLP statement. 

Duplicate vessels of sample solutions in sterile buffer solutions at pH’s 4.0, 7.0 and 9.0 were taken and the concentrations of the monoester (isobutyl dihydrogen phosphate) and the diester (diisobutyl hydrogen phosphate) were determined by HPLC-MS.

In the preliminary test (Tier 1), sample solutions were maintained at 50 °C for a period of 121 hours and more than 10% of degradation of the monoester was measured at pH 4 and 7 when the diester was found to be stable.

On undertaking Tier 2 testing for the monoester component, establishing sample solutions at test temperatures of 50, 60 and 70 °C, no significant hydrolysis was detected at either pH 4 or pH 7. Less than 10% hydrolysis was confirmed for multiple samples under incubation conditions much harsher than the preliminary test criterion of 50 °C for 120 hours. This indicated that the initial decrease in the monoester component concentrations observed in the Preliminary test/Tier 1 testing was not due to hydrolysis. 

The measured hydrolytic half-lives at 25 °C of the two main components of the reaction mass are greater than 1 year at any of the pH tested (4.0, 7.0 and 9.0).

The linearity of the detector response with respect to concentration for the HPLC-MS analytical parameters employed was previously assessed for water solubility study (Harlan Study Number 41200250). Over the tested concentration range a satisfactory, first order correlation coefficients of 1.000 were obtained for both components, a precision (replicate injection) relative standard deviation of 2.56% and a limit of quantification for the method to be at least 25 mg/L. The confirmation of linear response for the HPLC-MS analytical method was performed using standard solutions prepared in acetonitrile. The change in sample matrix for the hydrolysis analysis to acetonitrile: water: acetic acid (50:45:5 v/v/v) was concluded not to impact on the validity of this data. 

This statement was proved by a valid supporting study (Harlan Study Number 41300710) to confirm the linear response for the HPLC-MS analytical method using standard solutions prepared in the correct matrix (acetonitrile: water: acetic acid (50:45:5 v/v/v)). This study was performed according to scientifically sounds method and under GLP. In all matrices investigated, representative of those used during the hydrolysis study, both the monoester and diester components were confirmed to demonstrate first order correlation coefficient values of greater than or equal to 0.999 over a nominal concentration range (0 to 85 mg/L) incorporating those analyzed under the hydrolysis study.