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Partition coefficient

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Reference
Endpoint:
partition coefficient
Type of information:
experimental study
Adequacy of study:
key study
Study period:
14/09/2018 - 19/09/2018
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 123 (Partition Coefficient (1-Octanol / Water), Slow-Stirring Method)
Version / remarks:
2006
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Type of method:
slow-stirring method
Partition coefficient type:
octanol-water
Analytical method:
liquid chromatography
mass spectrometry
Key result
Type:
log Pow
Partition coefficient:
4.947
Temp.:
25 °C
pH:
6.6
Remarks on result:
other: ± 0.006
Details on results:
Statistics: Weighted average mean
Repeatability: Deviation ≤0.1 log
pH: 6.781, 6.109, 6.824 for replicates 1, 2 and 3
Temperature: 24.97°C, 25.05°C, 24.93°C for replicates 1, 2 and 3
Validity: Criteria for OECD 123 fulfilled; the mean log Pow values were within the range ± 0.3 log (≤ 0.1 log) and the temperature was 25 ± 1°C (24.97 ± 0.03 for replicate 1, 25.05 ± 0.03 for replicate 2 and 24.93 ± 0.04 for replicate 3)

Table 1 Partition coefficient results

Replicate Mean test duration (h) Measured concentration in n-octanol (mg/L) Measured concentration in aqueous phase (mg/L) Pow Single Log Pow Mean log Pow Standard deviation ± Coefficient of variation (%)
1 68.17 20058 0.278 72276 4.859 4.926 0.047 0.96
73.58 20129 0.217 92826 4.968
92.38 19049 0.215 88646 4.948
98.08 19939 0.234 85379 4.931
2 68.17 20017 0.247 80958 4.908 4.964 0.054 1.08
73.58 20741 0.191 108873 5.037
92.38 19687 0.216 91240 4.96
98.08 19465 0.219 88856 4.949
3 68.17 20151 0.249 81061 4.909 4.952 0.039 0.78
73.58 20177 0.203 99550 4.998
92.38 18927 0.22 85842 4.934
98.08 19747 0.214 92357 4.965
          Mean value 4.947    
          Weighted average log Pow 4.947    
          Weighted standard deviation 0.006    
Conclusions:
The log n-octanol / water partition coefficient for the test item was 4.947 at 25°C and pH 6.6.
Executive summary:

The n-octanol / water partition coefficient of the test item was determined according to OECD guideline 123 using the slow stirring method, selected due to the expected high log Pow for the test item, with four samples analysed from each of the three replicates. The validity criteria for OECD 123 were met for the study. The log partition coefficient was determined to be 4.947 at 25°C and pH 6.6.

Description of key information

The log n-octanol / water partition coefficient of isopentyl p-methoxycinnamate was determined to be 4.947 at 25°C and pH 6.6.

Key value for chemical safety assessment

Log Kow (Log Pow):
4.947
at the temperature of:
25 °C

Additional information

The n-octanol / water partition coefficient of the test item was determined according to OECD guideline 123 using the slow stirring method, selected due to the expected high log Pow for the test item, with four samples analysed from each of the three replicates. The validity criteria for OECD 123 were met for the study. The log partition coefficient was determined to be 4.947 at 25°C and pH 6.6.

In the supporting study, the partition coefficient of the test substance was measured using EU method A8 (shake flask method) with the aid of quantitative HPLC analysis. Solutions of the test substance (less than 0.01 M) were prepared, in triplicate, in n-octanol presaturated with Milli Q distilled, deionised water. Aliquots of these 3 solutions were mixed with varying ratios of Milli Q distilled, deionised water presaturated with n-octanol. Each of these solutions was prepared in duplicate. Thus, 6 test solutions were obtained. The solutions were placed in a shaking water bath for 2 h at 25.0±1°C. Each test solution was then centrifuged for 10 min at 2,000 rpm and then left to stand for at least 1 h at 25.0°C±1°C. The layers were separated using disposable pipettes into clean vials. Each layer was analysed quantitatively by HPLC. The partition coefficients obtained with the 6 test solutions ranged from 4.636 to 4.868. An average partition coefficient of 4.78 was calculated from these results.

As the test substance is not expected to be ionisable, the test substance was considered as being analysed in its neutral form in accordance with the test guidelines. The determined Log Kow fell within a range of ±0.3 log units. Therefore, as noted in the test guidelines, the accuracy of the test was rated acceptable. The applicable range for the shake flask method is 2 < log Kow< 4 (EU method A8). When the concentration of the solute in either phase is not more than 0.01 mol/L, this range may be extended to log Kow up to 5. As the concentrations of test substance do not exceed this value in the test, the shake flask method is an appropriate method to determine log Kow of test substance.