Sodium 2-[methyl(1-oxododecyl)amino]ethanesulphonate

Water solubility

Link to relevant study record(s)

Reference

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2018

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: ISO 4311

Principles of method if other than guideline:

The Critical Micellization Concentration (CMC) is determined by plotting of the graph of surface tension as a function of the logarithm of the concentration: the CMC corresponds to a singular point on this curve.

Ten solutions with different concentrations that bracket the expected critical concentration are prepared. After allowing the solutions to equilibrate at the desired test temperature, the surface tension is determined by ring method for each solution. The results are plotted as a primary curve (of surface tension as a function of concentration, which will include the region in which the CMC is located. According to the result obtained, six new solutions with closely related concentrations bracketing the CMC are prepared, either by weighing or by dilution of the stock solution. The solutions are gently agitated without stirring (taking care not to cause the formation of foam when testing strongly foaming products).The solutions are allowed to equilibrate at the required test temperature. Once 3 hours has elapsed from dissolution or dilution, whichever is the case, and until the desired temperature is attained, the surface tension of the solutions is determined. This time may be increased until the surface tension values become stable or the measurement may be commenced as soon as stability is reached. In the case of concentrations higher than the CMC the time for attaining equilibrium may be reduced to 15 minutes. Three successive measurements are carried out at 15 minute intervals at each concentration without rinsing the ring between each measurement. The pause before the measurement is adequate if the three successive measurements do not show any progressive systematic variation.

Each time the concentration is changed; the ring is rinsed with a suitable solvent (e.g. ethanol) then distilled water.

A graph of the mean surface tension vs. the logarithm of the concentrations, expressed in g.mL-1 is obtained from which the CMC is determined as;

(a) the point on the curve at which a sharp change of slope occurs, or
(b) the point on the curve at which the surface tension is considerably lower than that at higher concentrations (the abscissa of this "minimum" specifies, by definition, the range of CMC).

GLP compliance:

no

Type of method:

other: Determination of critical micelle concentration

Key result

Water solubility:

0.18 g/L

Conc. based on:

test mat.

Temp.:

20 °C

pH:

ca. 6.3

Details on results:

The surface tension vs. concentration plot shows a minimum. In accordance with ISO 4311, the CMC is taken as the minimum. The standard error in the cmc is estimated from the uncertainty of the slope of the low concentration branch of the plot.

The critical micelle concentration obtained is thus 0.180 g/l.

Conclusions:

Water solubility determined as critical micelle concentration: 0.180 g/L

Executive summary:

The critical micelle concentration of the test item was determined from a plot of surface tension versus concentration of the test item in water in a well reported study according to national testing guideline DIN ISO 4311. The critical micelle concentration is the most appropriate parameter describing water solubility of surface active materials.

Description of key information

Surfactants like SMLT can form dispersions or emulsions in which the bioavailablity for aquatic toxicity studies is difficult to ascertain, even with careful solution preparation. Micelle formation can result in an overestimation of the bioavailable fraction even when “solutions” are apparently formed. This presents significant problems of interpretation of aquatic toxicity test results for surface active materials. Hence, the solubility of SMLT has been investigated in terms of its 'bulk' solubility in accordance with OECD 105 and the freely dissolved monomolecular form as the critical micelle concentration (CMC).

SMLT was found to have a bulk solubility in water of 444 g/L. However, the CMC for SMLT is much lower, and was determined to be 0.18 g/L.

For the CSA, the key value for water solubility of the substance is taken as the CMC i.e. 0.18 g/L.

Key value for chemical safety assessment

Water solubility:

0.18 g/L

at the temperature of:

20 °C