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

Partition coefficient

Link to relevant study record(s)

Reference

Endpoint:

partition coefficient

Type of information:

calculation (if not (Q)SAR)

Adequacy of study:

key study

Study period:

December 2018

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

accepted calculation method

Justification for type of information:

Sodium Methyl Lauroyl Taurate (SMLT) is an Anionic Surface Acting Agent. This therefore affects the results of the Octanol-Water Partition Coefficient test, due to the emulsion that forms at the partition interface. Surface acting agents have the ability of altering the surface or interfacial energies of two immiscible phases, thus skewing the results of testing. According to OECD Testing Guidelines for Test Method 117 Partition Coefficient (n-octanol/water), High Performance Liquid Chromatography Method isn’t applicable for surface-active agents. According to OECD Testing Guidelines for Test Method 107, the Shake Flask method is impossible to use with surface-active agents. According to OECD Testing Guidelines for Test Method 123, Partition Coefficient (1-Octanol/Water), Slow Stirring method is not applicable for substances that display significant interfacial activity. So, as with the Shake Flask method and due to the properties of SMLI, coupled with its foaming capabilities it would impossible to separate the two immiscible solvents at the interface to obtain reliable results.

According to EU method A.8 (2008), shake flask (OECD 107) and HPLC (OECD 117) experimental methods are not applicable to surface active materials, for which a calculated value or an estimate based on the individual n-octanol and water solubilities should be provided. This recommendation is also mirrored in the ECHA Guidance R7a, specifically Section R.7.1.8.5.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 107 (Partition Coefficient (n-octanol / water), Shake Flask Method)

Deviations:

no

Principles of method if other than guideline:

As SMLT is surface active, the partition coefficient is estimated from the ratio of the solubility of the test material in pure n-octanol to its solubility in water.

A known amount of the sample (solid substances are pulverised) is placed in a stoppered 100 ml volumetric flask, where increasing volumes of n-octanol are added incrementally at ambient temperature.

After each addition of a known amount of octanol, the mixture is shaken vigorously for 10 minutes and is visually checked for any un-dissolved parts of the sample. This process is repeated until complete dissolution of the sample occurs. The approximate solubility of the sample is then obtained from the relation:

Octanol Solubility = Mass of sample/ Volume of n-octanol in which complete dissolution occurred

The procedure was repeated with known amount of sample in 100 ml volumetric flask, where increasing volumes of HPLC grade water are added at room temperature. The approximate solubility of the sample in water is then obtained from the relation:

Water Solubility = Mass of sample/Volume of water in which complete dissolution occurred.

However, since SMLT is surface active and can exhibit a 'bulk' solubility in water higher than the critical micelle concentration (CMC) it is prudent to take the CMC as a solubility limit, in order to avoid the artefact of unrealistically low Kow value (ECHA Guidance R7a; Section R.7.1.8.5). The CMC value for SMLT has been derived along with an estimation of it's 'bulk' solubility in water as part of a study conducted in accordance with OECD 105 summarised elsewhere in this dossier.

Using the CMC and n-octanol solubility data for SMLT, the Log Kow is then obtained from the relation:

Log Pow = Log (Solubility in octanol/Solubility in water as CMC)

GLP compliance:

yes (incl. QA statement)

Type of method:

estimation method (solubility ratio)

Key result

Type:

log Pow

Partition coefficient:

ca. -1.25

Temp.:

20 °C

pH:

6.27

Conclusions:

Using the known solubility of SMLT in n-octanol and water (as CMC), the log Kow of has been estimated to be -1.25.

Executive summary:

Sodium Methyl Lauroyl Taurate (SMLT) is an Anionic Surface Acting Agent. This therefore affects the results of the Octanol-Water Partition Coefficient test, due to the emulsion that forms at the partition interface. Surface acting agents have the ability of altering the surface or interfacial energies of two immiscible phases, thus skewing the results of testing. According to OECD Testing Guidelines for Test Method 117 Partition Coefficient (n-octanol/water), High Performance Liquid Chromatography Method isn’t applicable for surface-active agents. According to OECD Testing Guidelines for Test Method 107, the Shake Flask method is impossible to use with surface-active agents. According to OECD Testing Guidelines for Test Method 123, Partition Coefficient (1-Octanol/Water), Slow Stirring method is not applicable for substances that display significant interfacial activity. So, as with the Shake Flask method and due to the properties of SMLI, coupled with its foaming capabilities it would impossible to separate the two immiscible solvents at the interface to obtain reliable results.

According to EU method A.8 (2008), shake flask (OECD 107) and HPLC (OECD 117) experimental methods are not applicable to surface active materials, for which a calculated value or an estimate based on the individual n-octanol and water solubilities should be provided. This reccomendation is also mirrored in the ECHA Guidance R7a, specifically Section R.7.1.8.5.

Using the CMC and n-octanol solubility data for SMLT, the Log Kow is then obtained from the relation: Log Pow = Log (Solubility in octanol/Solubility in water as CMC)

Whereby:

Solubility of SMLT in n-octanol is taken as 0.01 g/L

Solubility of SMLT in water is taken as the CMC value which is 0.18 g/L

Hence the log Kow of SMLT is estimated to be -1.25 which is within reasonable agreement (within a one log unit) of the value of -0.44 calculated by QSAR (US EPA KOWWIN)

Description of key information

Sodium Methyl Lauroyl Taurate (SMLT) is an Anionic Surface Acting Agent. This therefore affects the results of the Octanol-Water Partition Coefficient test, due to the emulsion that forms at the partition interface. Surface acting agents have the ability of altering the surface or interfacial energies of two immiscible phases, thus skewing the results of testing. According to OECD Testing Guidelines for Test Method 117 Partition Coefficient (n-octanol/water), High Performance Liquid Chromatography Method isn’t applicable for surface-active agents. According to OECD Testing Guidelines for Test Method 107, the Shake Flask method is impossible to use with surface-active agents. According to OECD Testing Guidelines for Test Method 123, Partition Coefficient (1-Octanol/Water), Slow Stirring method is not applicable for substances that display significant interfacial activity. So, as with the Shake Flask method and due to the properties of SMLI, coupled with its foaming capabilities it would impossible to separate the two immiscible solvents at the interface to obtain reliable results

According to EU method A.8 (2008), shake flask (OECD 107) and HPLC (OECD 117) experimental methods are not applicable to surface active materials, for which a calculated value or an estimate based on the individual n-octanol and water solubilities should be provided. However, it is then be prudent to take the critical micelle concentration in water (CMC) as a solubility limit, in order to avoid the artefact of unrealistically low Kow value (ECHA Guidance R7a; Section R.7.1.8.5). The CMC value for SMLT has been derived along with an estimation of it's 'bulk' solubility in water as part of a study conducted in accordance with OECD 105 summarised elsewhere in this dossier.

Therefore, the log Kow of SMLI has been calculated using two methods:

i) Estimation method based on ratio of solubility in n-octanol and water (as CMC) and;

ii) QSAR calculation with US EPA Episuite KOWWIN model

The log Kow value obtained from the estimation method is used as the key value for the CSA i.e. log Kow = -1.25

Key value for chemical safety assessment

Log Kow (Log Pow):

-1.25

at the temperature of:

20 °C