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Dissociation constant

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Reference
Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 112 (Dissociation Constants in Water)
Deviations:
no
Qualifier:
according to
Guideline:
EPA OPPTS 830.7370 (Dissociation constants in water)
Deviations:
no
GLP compliance:
yes
Dissociating properties:
no
No.:
#1
Temp.:
20 °C
Remarks on result:
other: The test substance does not dissociate under the test conditions and therefore has no dissociation constant.
Conclusions:
The test substance does not dissociate under the test conditions and therefore has no dissociation constant.
Executive summary:

This study was conducted to determine the dissociation constant of the test substance according to OECD Guideline No. 112 and OPPTS 830.7370 guidelines.

The test solution concentration used [50 μg/mL for titration method and 9.6 μg/mL for spectrophotometric method] was well below the water solubility (230 mg/L) of the test material.

Experiments for determination of dissociation constant of the test substance were carried out by titrating a 50 μg/mL solution of test substance in double distilled water with a 0.0024 M standardized sodium hydroxide solution and 0.0024 M standardized hydrochloric acid solution, separately. The dissociation was examined by measuring the change in pH of the test solution after incremental additions of the standardized sodium hydroxide solution and separately by standardized hydrochloric acid solution.

As per the resulting graphs of titration of the test substance solution with 0.0024 M sodium hydroxide solution and 0.0024 M hydrochloric acid solutions, there were no prominent equivalence points and hence, it was considered that the test item does not dissociate under the test conditions.

The results obtained by the titration method were further confirmed with the spectrophotometric method by recording the UV-VIS absorption spectra of test item solutions under six different pH conditions (pH 1.0, 2.2, 5.8, 7.5, 9.1 and 10.8) and checking for any significant difference in the resulting spectra. No significant differences in the spectra of the test substance in buffers of different pH were noticed and hence, it was concluded that the test substance does not dissociate under the test conditions.

Based on the results of titration and spectrophotometric methods, it was concluded that the test substance does not dissociate under the test conditions and therefore has no dissociation constant.

Description of key information

OECD Guideline 112

Key value for chemical safety assessment

Additional information

The test substance does not dissociate under the test conditions and therefore has no dissociation constant.