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Water solubility

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water solubility
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
according to guideline
EU Method A.6 (Water Solubility)
GLP compliance:
yes (incl. QA statement)
Type of method:
flask method
Key result
Water solubility:
1.05 g/L
20 °C
Details on results:
The water solubility of the test material was estimated using the critical micelles concentration (CMC) approach. From the CMC analysis the water solubility was estimated as 0.941 g/L. Because this solubility is greater than 10 mg/L, shaking equilibration was selected for the analysis.

Saturation of Water with Test Material
As the test material forms micelles, concentrations of approximately 1.5 times the estimated solubility were prepared instead of 5 times the estimated solubility. About 0.0637 g, 0.0623 g and 0.0656 g of the test material was used to saturate 50 mL of water in each flask (labelled 1, 2 and 3 respectively). The three flasks were then shaken at a temperature of 30°C in an incubated shaker at 80 rpm for durations of 24 hours (for Flask 1), 48 hours (for Flask 2) and 72 hours (for Flask 3). Each flask was then allowed to equilibrate for a minimum of 24 hours prior to concentration analysis. The solutions in the flasks were centrifuged, and then filtered to 0.20 µm with a syringe filter before the analysis. It was noted that undissolved material was observed in all three flasks.

Analytical Determination of Water Solubility
Aliquots of the supernatant of the saturated aqueous solutions were centrifuged, filtered to 0.20 µm, and then diluted by a factor of 40. The diluents were analysed using the Shimadzu PC1650 PC spectrophotometer. The concentration obtained was therefore multiplied by the dilution factor to obtain the actual concentration of each of the saturated solutions.
From the concentration analysis the water solubility of the test material as obtained from Flask 2 was comparatively higher than the concentration from Flasks1 and 3. The high concentration observed from analysis of Flask 2 was suspected to have been caused by aggregates of micelles of size less than 0.20 µm.
These aggregates may have passed through the syringe filter into solution prior to the dilutions. As a result the water solubility of the test material was calculated from the mean of the concentrations of Flasks 1 and 3 which are within 2 %.

The water solubility of the test substance was therefore determined as 1.05 g/L.

Analytical determinations of water solubility:

 Flask N°  pH  Absorbance 1  Absorbance 2  Absorbance 3
 1 8.00 0.0166 0.0167 1.05 
 2 7.95 0.0179 0.0178 1.12 
 3 8.13 0.0165 0.0166  1.04
The water solubility of test material was determined as 1.05 g/L.

Description of key information

The water solubility of the test substance was determined to 1.05 g/L at 20°C, in a GLP study according to the flask method as specified in test method EC A.6 (Younis, 2013).

Key value for chemical safety assessment

Water solubility:
1.05 g/L
at the temperature of:
20 °C

Additional information

In addition to the flask method, the Critical Micelle Concentration (CMC; the concentration above which micelles are formed) was determined to be 0.941 g/L. The CMC is regarded as the true water solubility as at higher concentrations all additional surfactant added to the system goes to micelles. In the flask method (EC A.6) precautions were taken to exclude micelles when analysing the samples (centrifugation / filtration). As the results from the CMC determination and the flask method (EC A.6) are in agreement (the EC A.6 flask method accepts a repeatability ≤15%) the value from the flask method (1.05 g/L) is used as the key value for chemical safety assessment.

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