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Physical & Chemical properties

Partition coefficient

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Description of key information

Experimental value of Log Pow at 25°C: 2.10 

Key value for chemical safety assessment

Log Kow (Log Pow):
at the temperature of:
25 °C

Additional information

The test item is a suface-active agent, so the traditional method used for the determination of the partition coefficient (HPLC and Shake flask method) do not apply. Indeed, with the shake flask method the test item could forms micelle at the interphase of the n-octanol and the water phase.

The HPLC method was applied to Cocamidopropyl hydroxysultaine C8-18. A weighted average value of 1.38 was obtained but the test could not be considered as reliable for the following reasons:

- the HPLC method is questionable for surface active substances as there is no surface active reference compounds with known log Pow can't be employed as there as no surface active reference compounds with known experimental value of partition coefficient.

- a derivation from the guideline (Method 117 OECD) was observed in the test: the value of Pow derived from two measurements made under identical conditions and using the same set of reference substances is deviated by more than 0.1 log units.

- several other reason linked to characteriscal of the sample and deficiencies in the analytical method are explained in the ESR.

The computational method can't be applied neither as the test item forms a no dissolved phase in n-octanol. That's why the slow stirring method was chosen for the determination of the partition coefficient of the test item. Indeed, this method reduces the formation of microdroplets in the water phase. The stirring introduces limited turbulence which enhances the exchange between n-octanol and water without microdroplets being formed. As a consequence, overestimation of the aqueous concentration due to the test substance molecules associated to such droplets does not occur.

The determination of the partition coefficient in the key study was performed according to Method 123 of OECD Guidelines of 23 March 2006 and GLP. No deviation of the guidelines was observed during the test.

The test item is a UVCB so it was decided to develop the analytical method based on the surfactant part of the test item (alkylamidopropylhydrosultaine) to quantify the test item in water and in n-octanol . The alkylamidopropylhydroxysultaine part of the test item is composed in majority by the C12 fraction.