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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:
25-Jul to 02-Aug-2018
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
comparable to guideline study
Reason / purpose:
reference to same study
Qualifier:
equivalent or similar to
Guideline:
other: Due to the complex nature and composition of the test item, the water solubility was expressed in terms of the critical micelle concentration (CMC).
Version / remarks:
EU Method A.5 (surface tension)
Qualifier:
equivalent or similar to
Guideline:
other: Due to the complex nature and composition of the test item, the water solubility was expressed in terms of the critical micelle concentration (CMC).
Version / remarks:
OECD 115 (surface tesnion)
GLP compliance:
no
Type of method:
other: EU Method A.5 and OECD 115; water solubility expressed in terms of the critical micelle concentration.
Water solubility:
49 mg/L
Temp.:
20 °C
pH:
> 5.8 - < 7.6

Results

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)

Log10 Concentration

Mean Surface Tension (mN/m)

Solution pH

5.021 x 103

3.701

36.5

7.6

1.004 x 103

3.002

37.5

6.9

301.2

2.479

38.7

6.4

100.4

2.002

40.7

6.0

30.12

1.479

44.2

5.8

10.04

1.002

52.2

5.9

3.012

0.479

62.7

5.8

1.004

0.002

66.5

5.8

0.3012

-0.521

70.5

5.8

0.1004

-0.998

72.0

5.8

 

The results were used to plot log10 [concentration (mg/L)] versus surface tension (mN/m).

Line 1 was generated from linear regression of 3 sample solution concentrations for which the surface tension was shown to be concentration dependent and Line 2 was generated from linear regression of 2 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:

Line1 equation:  y = -18.5x+71.3

Line 2 equation: y = -1.78x +43.0

 

The sample solution at 100.4 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 1.004, 0.3012 and 0.1004 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 48.9 mg/L.

 

Discussion

The critical micelle concentration (CMC) is an important characteristic of a surfactant. At low concentrations of surfactant, the surface tension of water is only slightly affected. Increasing the concentration but before reaching the CMC, the surface tension changes significantly. After reaching the CMC and above, the surface tension remains relatively constant or changes with a much more gradual slope.

 

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.

 

Conclusion

The critical micelle concentration of the test item was determined to be 49 mg/L at 20.0 ± 0.5 °C.

Description of key information

49 mg/L at 20 °C (critical micelle concentration (CMC) determination, OECD 115)

Key value for chemical safety assessment

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

Additional information