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Physical & Chemical properties

Water solubility

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Reference
Endpoint:
water solubility
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2017-2018
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
comparable to guideline study
Qualifier:
according to
Guideline:
other:
Version / remarks:
Critical micelle concentration (CMC) method
Principles of method if other than guideline:
For surface active substances the Critical Micelle Concentration (CMC) method is used as an alternative to the water solubility. The critical micelle concentration (CMC) is determined by measuring the surface tension of test substance solutions at different test substance concentrations. For surface active substances which form micelles in solution, the surface tension decreases with increasing concentration until the CMC is reached. At concentrations above the CMC, the surface tension remains constant. The CMC is determined from a plot of the surface tension versus the logarithm of the test substance concentration.
GLP compliance:
yes (incl. certificate)
Type of method:
other: Critical Micelle Concentration
Key result
Water solubility:
13.1 g/L
Temp.:
20 °C
Remarks on result:
other: The water solubility has been assessed on the basis of the critical micelle concentration

The readings and temperatures for the sample solutions are shown in the following table:

Concentration (mg/L)

Reading
(mN/m)

Temperature
(°C)

Concentration (mg/L)

Reading
(mN/m)

Temperature
(°C)

3.05 x 105

35.5

20.0

1.00 x 103

39.5

20.0

34.5

20.0

38.5

20.0

34.5

20.0

38.5

20.0

34.5

20.0

38.5

20.0

1.00 x 105

35.5

20.0

301

42.5

20.0

34.5

20.0

42.0

20.0

34.5

20.0

42.0

20.0

34.5

20.0

42.0

20.0

3.05 x 104

34.0

20.0

100

44.0

20.0

33.0

20.0

43.5

20.0

33.0

20.0

43.5

20.0

33.0

20.0

43.5

20.0

1.00 x 104

33.0

20.0

30.1

47.5

20.0

32.5

20.0

46.5

20.0

32.5

20.0

46.5

20.0

32.5

20.0

46.5

20.0

3.01 x 103

36.5

20.0

10.0

51.5

20.0

35.5

20.0

48.5

20.0

35.5

20.0

48.5

20.0

35.5

20.0

48.5

20.0

 

The concentration (mg/L), log10[concentration (mg/L)] and mean surface tension values for the sample solutions are shown in the following table:

Concentration
(mg/L)

Log10Concentration

Mean Surface
Tension (mN/m)

Solution pH

10.0

1.00

48.5

5.76

30.1

1.48

46.5

6.02

100

2.00

43.5

6.29

301

2.48

42.0

6.60

1.03 x 103

3.00

38.5

6.94

3.01 x 103

3.48

35.5

7.32

1.00 x 104

4.00

32.5

7.76

3.05 x 104

4.48

33.0

8.10

1.00 x 105

5.00

34.5

8.42

3.05 x 105

5.48

34.5

8.59

 

Conclusions:
The CMC was determined to be 13.1 g/L.
Executive summary:

The water solubility of the test item has been investigated experimentally.

Initially the water solubility method (EC A.6/OECD 105) was considered. However, preliminary work showed that due to the high surface activity, the test item dispersed and it was not possible to clean up excess test item from the samples. Therefore, the water solubility has been assessed on the basis of the critical micelle concentration (CMC).

Below the CMC, a surfactant is considered to be thermodynamically soluble in the water; whereas above the CMC, the solubility of a surfactant in water has been exceeded and the excess surfactant aggregates to form micelles. These micelles have significantly less effect on the surface tension of a solution and are considered not to be in solution. Thus, the water solubility of a surfactant may be expressed in terms of the CMC. The critical micelle concentration of the test item was determined to be 13.1 g/L at 20.0 ±0.5 °C.

Description of key information

When assessing water solubility as part of method development it became apparent that the test item is highly surface active and this presents potential issues with water solubility determination.

Even applying a slower shaking speed during sample preparation or a slow stir type method samples with suspended/emulsified excess were found being problematic, as the test item is solid with a density greater than that of water, thus creating disturbance by undissolved test item. Therefore, the water solubility has been assessed on the basis of the critical micelle concentration (CMC) instead.

By this method, a solubility of 13.1 g/L was determined at 20 °C.

Key value for chemical safety assessment

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

Additional information