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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:
From October 20, 2017 to January 31, 2018
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study
Reason / purpose:
reference to same study
Qualifier:
according to
Guideline:
other: OECD Guideline 115: Surface Tension of Aqueous Solutions
Version / remarks:
27 July 1995
Deviations:
no
Qualifier:
according to
Guideline:
other: EU Method A5: Surface tension
Version / remarks:
30 May 2008
Deviations:
no
Principles of method if other than guideline:
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.
GLP compliance:
no
Remarks:
The study was conducted in a facility which operates in accordance with Good Laboratory Practice principles; however no claim of GLP compliance was intended nor is made for this study
Type of method:
other: by determining the surface tension of a range of aqueous sample solutions of differing concentration
Key result
Water solubility:
ca. 65 mg/L
Conc. based on:
test mat.
Incubation duration:
ca. 10 min
Temp.:
20 °C
pH:
ca. 4.82
Remarks on result:
other: CMC - water solubility equivalent for surfactants; value rounded off to 65 mg/L
Details on results:
Please see below table.

Results

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

Table1: Surface tension values

Concentration (mg/L)

Reading (mN/m)

Temperature (°C)

1.001 x 104

40.0

20.0

40.0

20.0

40.0

20.0

3.002 x 103

40.5

20.0

40.5

20.0

40.5

20.0

1.001 x 103

41.0

20.0

41.0

20.0

41.0

20.0

300.2

42.0

20.0

42.0

20.0

42.0

20.0

100.1

44.0

20.0

45.0

20.0

45.5

20.0

45.5

20.0

30.02

50.5

20.0

50.5

20.0

51.0

20.0

15.01

49.5

20.0

53.5

20.0

56.0

20.0

56.0

20.0

56.5

20.0

10.01

60.5

20.0

60.5

20.0

62.5

20.0

62.5

20.0

62.5

20.0

3.002

70.5

20.0

71.0

20.0

71.0

20.0

1.001

72.0

20.0

72.5

20.0

72.5

20.0

Mean surface tension values were based on the last three readings for a particular concentration which were considered to be constant.

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

 

Table 2: The concentration (mg/L), log10 [concentration (mg/L)] and mean surface tension values

Concentration
(
mg/L)

Log10Concentration

Mean Surface Tension (mN/m)

Solution pH

1.001 x 104

4.000

40.0

3.70

3.002 x 103

3.477

40.5

3.78

1.001 x 103

3.000

41.0

3.86

300.2

2.477

42.0

4.23

100.1

2.000

45.3

4.54

30.02

1.477

50.7

5.09

15.01

1.176

56.2

5.32

10.01

1.000

62.5

5.43

3.002

0.4774

70.8

5.67

1.001

0.0004

72.3

5.60

The plot of log10 [concentration (mg/L)] versus surface tension (mN/m) was drafted. For graph, kindly refer the attached background material section.

Line 1 (red) was generated from linear regression of 3 sample solution concentrations for which the surface tension was shown to be concentration dependent and Line 2 (green) was generated from linear regression of 3 sample solution concentrations for which the surface tension was observed to be essentially independent of concentration. The intersection of these two lines gave the critical micelle concentration and was calculated by solving the two equations:

Line 1 equation: y = -24.0 x + 85.8

Line 2 equation: y = -0.999 x + 44.0

The sample solution at 100.1 mg/L was not used in generating the two lines. At this concentration the surface tension appeared to be transitioning to Line 2 at a shallower gradient than Line 1. The sample solutions at 3.002 and 1.001 mg/L were not used in generating the two lines. At this concentration the surface tension was only slightly affected and was approaching that of purified water.

The CMC was determined to be 64.9 mg/L.

Conclusions:
Under the study conditions, the the CMC or water solubility of the test substance was determined to be 65 mg/L at 20.0 ± 0.5°C.
Executive summary:

A study was conducted to determined the water solubility of the test substance based on critical micelle concentration (CMC), according to OECD Guideline 115 and EU Method A.5, in compliance with GLP. Due to the surface activity of the test substance, the CMC value was considered as a water soluibility equivalent in accordance with the ECHA R.7a Guidance. Under the study conditions, the CMC of the test substance was determined to be 65 mg/L at 20.0 ± 0.5°C (Envigo, 2018).

Description of key information

Water solubility of the test substance was determined based on critical micelle concentration (i.e., a water solubility equivalent of surfactant), according to OECD Guideline 115 and EU Method A.5 (Envigo, 2018).

Key value for chemical safety assessment

Water solubility:
65 mg/L
at the temperature of:
20 °C

Additional information

(based on CMC)