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Administrative data

dissociation constant
Type of information:
experimental study
Adequacy of study:
key study
Study period:
16/04/2018 - 31/08/2018
1 (reliable without restriction)

Data source

Reference Type:
study report

Materials and methods

Test guideline
according to guideline
OECD Guideline 112 (Dissociation Constants in Water)
GLP compliance:
yes (incl. QA statement)

Test material

Constituent 1
Chemical structure
Reference substance name:
Bismuth citrate
EC Number:
EC Name:
Bismuth citrate
Cas Number:
Molecular formula:
bismuth(3+) 2-hydroxypropane-1,2,3-tricarboxylate
Test material form:
solid: particulate/powder
migrated information: powder
Details on test material:
Product name: Bismuth Citrate
Specific details on test material used for the study:
Batch/Lot Number: 2018000872

Results and discussion

Dissociating properties:
not determined
Dissociation constant of the test item could not be determined under the conditions of this study.

Any other information on results incl. tables

Due to the low solubility of the test item, low concentrations of the titrant were used during the titration as well. Determination of the dissociation constant could not be performed because small change in the concentration of the titrant (in case of the higher concentration) caused significantly large increase in the pH. Hence the titration curves showed that the pH of the test system was adjusted for the pH of the titrant too rapidly for the pKa measurement to be made. (The lowest concentration of the titrant showed no significant pH increased which was caused by the low concentration.)

In conclusion the test system was very sensitive due to the low concentrations.

Applicant's summary and conclusion

Dissociation constant cannot be calculated because of low solubility. As the substance does not dissolve, it cannot dissociate in water.
Executive summary:

The dissociation of a chemical in water is of importance in assessing its impact upon the environment. It governs the form of the substance which in turn determines its behaviour and transport. It may affect the adsorption of the chemical on soils and sediments and adsorption into biological cells.

According to the OECD No. 112 guideline, three methods are available for dissociation constant determination. As the test item had no light absorption properties, the spectrophotometric method could not be used. As approximately 0.1 M solution of the test item was not achievable, the conductometry method could not be used either. Therefore, the titration method was applied.

Dissociation constant of the test item could not be determined under the conditions of this study. It was considered that the low solubility of the test item prevented the titration method from being feasible (the titration method is not suitable for low solubility substances).