Benzoic acid, 2-hydroxy-, mono-C14-18-alkyl derivs., calcium salts (2:1)

Dissociation constant

Administrative data

Endpoint:

dissociation constant

Data waiving:

study technically not feasible

Justification for data waiving:

the study does not need to be conducted because the substance is insoluble

Justification for type of information:

The OECD 112 test guideline presents three testing options for determination of the dissociation constant of a test substance in water. The three tests are identified and described in the test guideline as the titration, spectrophotometric and conductometric methods. Significant effort was expended in two of these three methods to try and determine this parameter for the material however this proved to be not technically feasible within the boundaries of the tests. The third test was not considered by the Sponsor to be likely to succeed based on the low water solubility and the results of the other two tests. Agreement was therefore reached with the laboratory that the dissociation constant could not be established for this material.
An expert statement by the laboratory is attached outlining the methodology used (Dissociation constant statement).

Details as follows:
Testing could not be carried out according to either the titrimetric or spectrophotometric methods. According to OECD 112, the test substance may not exceed one half the water saturation concentration. Wildlife International, Ltd. conducted a water solubility study using the column elution method (OECD 105) for the test material in reagent water at 20ºC (Wildlife International, Ltd. project number 523C-137). The water solubility was reported as 1.91 ± 0.06 mg/L (CV = 3.2%, n = 10).

According to OECD 112 “The titration method is not suitable for low solubility compounds.” Due to the water solubility of the test material being too low for the titration method, the spectrophotometric method was evaluated. Feasibility trials for the spectrophotometric method were conducted from August 2 – 3, 2012. Tyndall effect was monitored using a white light source to determine the potential presence of fine colloidal suspensions – an indication of water insolubility. Photometric analyses were conducted between 190 – 800 nm. A 500 mg/L fortification stock for the test substance was prepared in THF. Seven aqueous buffer solutions (pH = 4 through pH = 10) were fortified with the test material at a nominal concentration of 1 mg/L using a 500 mg/L THF stock of the test substance. The percent co-solvent for each fortified buffer solution was 0.2%. Tyndall effect was not present in any of these samples. However, most spectra had negative absorbance values for their respective wavelength maxima. Low absorbance values across the spectral range would result in little to no extinction coefficient differences as a function of pH.

Additional photometric analyses were performed at concentrations above the water solubility for the test substance. The test material was fortified into reagent water at 5.0 ppm. Co-solvent levels for these particular tests were 1.0%. Although more favorable, enhanced absorbances were obtained, the presence of the Tyndall effect – indicating water insolubility at that level - precluded further testing at higher concentrations.

It was concluded that dissociation constant determinations would not be feasible for the test material using either the titration or spectrophotometric methods. It is noted, however, that the conductivity test does require the preparation of a 0.1M aqueous solution of the test substance. The low water solubility of the material has already been documented.

Results and discussion

Dissociating properties:

not determined

Applicant's summary and conclusion

Conclusions:

Test not technically feasible, no dissociation constant can be determined.

Executive summary:

The OECD 112 test guideline presents three testing options for determination of the dissociation constant of a test substance in water. The three tests are identified and described in the test guideline as the titration, spectrophotometric and conductometric methods. Significant effort was expended in two of these three methods to try and determine this parameter for the material however this proved to be not technically feasible within the boundaries of the tests. The third test was not considered by the Sponsor to be likely to succeed based on the low water solubility and the results of the other two tests. Agreement was therefore reached with the laboratory that the dissociation constant could not be established for this material. An expert statement by the laboratory is attached in Section 13, please refer to this for full description of work conducted.