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Adsorption / desorption

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The adsorption / desorption study is technically not feasible, neither by OECD 106, nor according to OECD 121.

The study according to OECD 106 was not technically feasible because based on the technical factors hampering a robust analysis of fatty acid C16-18, sodium salt in soil matrix combined with the fact that the test item itself precipitated in presence of 0.01 M CaCl2 (considering that a certain minimum concentration is needed to successfully accomplish an OECD 106 study), it was concluded that the analytical method was hampered by too many technical issues in order to carry a valid and successful OECD 106 study out.

The study according OECD 121 was not technically feasible because the test item fatty acid C16-18, sodium salt is readily protonized in aqueous solution and results in the free fatty acid. thus the determination of adsorption coefficient by HPLC method is not possible as the protonized free acids will interact with the HPLC column, not the salt. Only in buffered solutions with pH values > 11 the equilibrium can be shifted towards the deprotonized fatty acid C16-18, sodium salt. Unfortunately the required stationary phases are not stable at these elevated pH values. Moreover, the recommended reference substance according to OECD 121 show no ionic structure so that the interaction of the test item and the reference items with the stationary phase is not comparable. Calibration with non-ionic compounds and determination of the sodium salt will therefore lead to erroneous results. Consequently, the determination of adsorption coefficient of the test item fatty acid C16-18, sodium salt by HPLC method is not possible.