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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 November 06, 2017 to March 05, 2018
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
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. 35 mg/L
Conc. based on:
test mat.
Incubation duration:
ca. 15.75 h
Temp.:
20 °C
pH:
ca. 5.76
Remarks on result:
other: Water solubility determined as CMC
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)

1.002 x 104

30.0

20.0

30.0

20.0

30.0

20.0

3.205 x 103

30.5

20.0

30.5

20.0

30.5

20.0

1.068 x 103

34.0

20.0

34.0

20.0

34.0

20.0

320.5

37.0

20.0

37.0

20.0

37.0

20.0

96.16

39.0

20.0

40.0

20.0

40.5

20.0

42.0

20.0

42.0

20.0

42.0

20.0

32.05

43.0

20.0

45.0

20.0

45.0

20.0

45.0

20.0

9.616

49.0

20.0

52.0

20.0

52.0

20.0

52.0

20.0

3.205

61.0

20.0

61.0

20.0

61.0

20.0

0.9616

71.0

20.0

71.0

20.0

71.0

20.0

0.3205

73.0

20.0

73.0

20.0

73.0

20.0

0.09616

73.0

20.0

73.0

20.0

73.0

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

1.002 x 104

4.001

30.0

6.56

3.205 x 103

3.506

30.5

6.47

1.068 x 103

3.029

34.0

6.13

320.5

2.506

37.0

6.08

96.16

1.983

42.0

5.84

32.05

1.506

45.0

5.67

9.616

0.983

52.0

5.51

3.205

0.506

61.0

5.51

0.9616

-0.017

71.0

5.58

0.3205

-0.493

73.0

5.86

0.09616

-1.017

73.0

5.69

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 4 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 = -19.0 x + 70.7

Line 2 equation: y = -4.94 x + 49.0

The sample solution at 32.05 and 96.16 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 0.3205 and 0.09616 mg/Lwere 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 34.8 mg/L.

Conclusions:
Under the study conditions, the the CMC or water solubility of the test substance was determined to be 35 mg/L at 20.0 ± 0.5°C.
Executive summary:

A study was conducted to determine the critical micelle concentration (i.e., water solubility equivalent for surfactants) of the test substance by determining the surface tension of a range of aqueous sample solutions of differing concentration, according to OECD Guideline 115 and EU Method A.5. 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 or water solubility of the test substance was determined to be 35 mg/L at 20.0 ± 0.5°C (Envigo, 2018).

Description of key information

The water solubility of the test substance was determined based on critical micelle concentration (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:
35 mg/L
at the temperature of:
20 °C

Additional information

Water solubility: 35 mg/L (based on CMC)