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Diss Factsheets

Administrative data

water solubility
Type of information:
experimental study
Adequacy of study:
key study
Study period:
12 January2018 - 19 July 2018
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference Type:
study report
Report date:

Materials and methods

Test guideline
according to guideline
other: Method A5 Surface Tension of Commission Regulation (EC) No 440/2008 of 30 May 2008 and Method 115 of the OECD Guidelines for Testing of Chemicals, 27
GLP compliance:
Type of method:
other: the critical micelle concentration (CMC) method was determined

Test material

Constituent 1
Test material form:
semi-solid (amorphous): gel

Results and discussion

Water solubility
Key result
Water solubility:
ca. 5.54 mg/L
Conc. based on:
other: critical micelle concentration (CMC)
20 °C
> 6.13 - <= 7.39

Any other information on results incl. tables

Refer to attached figure.  

Line 1 (red) was generated from linear regression of 2 sample solution concentrations for which the surface tension was shown to be concentration dependent and Line 2 (green) was generated from linear regression of 5 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 = -43.0x + 65.1 Line 2 equation: y = -1.29x + 34.2

The sample solutions at 0.3024 and 0.1008 mg/L were not used in generating the two lines.

The CMC was determined to be 5.54 mg/L.

Applicant's summary and conclusion

The critical micelle concentration of the test item was determined to be 5.5 mg/L at 20.0 ± 0.5 °C.
Executive summary:

Initially the water solubility method (EC A.6/OECD 105) was considered. A sample of 0.5191 g of test item and approximately 25 mL of purified water was shaken at 100 rpm for 10 minutes. After which, the sample was hazy with excess test item that had not dispersed. After vigorous shaking, the excess test item broke up and had foam on the surface. Clumps formed on standing and the solution was left clear. After allowing to stand overnight and then passing an aliquot through a 0.2 μm membrane filter, the solution was clear but with excess test item and a definitive Tyndall beam. This indicated that excess test item could not be completely removed from a solution as required by the water solubility method guidelines and that result would possibly vary with different loading rate. Therefore, the critical micelle concentration (CMC) method was attempted.

The 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.