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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:
January 2013 to March 2013
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP guideline study (OECD 123) with minor deviation
Qualifier:
according to
Guideline:
OECD Guideline 123 (Partition Coefficient (1-Octanol / Water), Slow-Stirring Method)
Deviations:
yes
Remarks:
A sampling time point was taken at 122h; this sampling was separated from the former sampling (118h) by a period of 4 hours instead of 5 hours minimum as specified in the guideline. this deviation does not have any impact on the result.
GLP compliance:
yes (incl. certificate)
Type of method:
shake-flask method to: flask method
Partition coefficient type:
octanol-water
Analytical method:
high-performance liquid chromatography
Type:
log Pow
Partition coefficient:
4.4
Temp.:
25 °C
pH:
7.6 - 7.9
Details on results:
See "Any other information on results incl. tables"

The results in the two phases at each time are given in the following table:

  

Vessel Number and

Sampling time

Concentration in the aqueous phase (mg/L)

 

Concentration in the 1-octanol phase (mg/L)

Pow Ratio

Log Pow

13-006 Y1 T = 98H

0.84

19550

23273.8

4.37

13-006 Y2 T = 98H

0.78

19250

24679.5

4.39

13-006 Y3 T = 98H

0.78

19350

24807.7

4.39

13-006 Y1 T = 118H

0.84

18900

22500.0

4.35

13-006 Y2 T = 118H

0.78

19300

24743.6

4.39

13-006 Y3 T = 118H

0.76

19150

25197.4

4.40

13-006 Y1 T = 122H

0.80

18950

23687.5

4.37

13-006 Y2 T = 122H

0.74

18850

25473.0

4.41

13-006 Y3 T = 122H

0.74

18750

25337.8

4.40

13-006 Y1 T = 138H

0.74

19000

25675.7

4.41

13-006 Y2 T = 138H

0.74

18900

25540.5

4.41

13-006 Y3 T = 138H

0.72

18450

25625.0

4.41

13-006 Y1 T = 143H

0.78

19600

25128.2

4.40

13-006 Y2 T = 143H

0.76

19750

25986.8

4.41

13-006 Y3 T = 143H

0.72

19300

26805.6

4.43

 

 

The average value of log Pow of the different vessel units is calculated as the average of the results of the individual experimental units weighed with their respective variances.

 

The results are shown in the following table.

  

Vessel Y1

Mean value Y1

Standard

Deviation

Y1

Vessel Y2

Mean value Y2

Standard

Deviation

Y2

Vessel Y3

Mean value Y3

Standard

Deviation

Y3

4.37

4.35

4.37

4.41

4.40

4.38

0.000480

4.39

4.39

4.41

4.41

4.41

4.40

0.000096

4.39

4.40

4.40

4.41

4.43

4.41

0.000184

  

Mean/vessel

Variance

Weighed average

4.38

0.000480

4.40

4.40

0.000096

4.41

0.000184

 

 

Conclusions:
Using the low stirring method, it was shown that the weighted average value of the 1-octanol/water partition coefficient log10 Pow of tert-butyl cumyl peroxide is equal to 4.40 ± 0.02 at 25 ± 1 °C.
Executive summary:

The partition coefficient n-octanol/water (Kow) of tert-butyl cumyl peroxide was estimated using the slow-stirring method. The Kow test was performed in accordance with the OECD 123 guideline. It was shown that the weighted average value of the 1-octanol/water partition coefficient log10 Pow of the substance is equal to 4.40 ± 0.02 at 25 ± 1 °C.

Description of key information

Using the slow stirring method, it was shown that the weighted average value of the 1-octanol/water partition coefficient log10 Pow of tert-butyl cumyl peroxide is equal to 4.40 ± 0.02 at 25 ± 1 °C.

Key value for chemical safety assessment

Log Kow (Log Pow):
4.4
at the temperature of:
25 °C

Additional information

The partition coefficient n-octanol/water (Kow) of tert-butyl cumyl peroxide was firstly determined by applying the HPLC method according to OECD Guideline 117. Two peaks were detected. The first peak shows a mean log Kow at 3.50 and the other peak a mean log Kow at 4.94. It’s assumed that the second peak corresponds to the test substance with a measured log Kow (= 4.94) similar to the estimation with QSAR model KowWin (= 4.66).

However it's known that the HPLC method is not accurate and overestimates results. As a consequence the partition coefficient n-octanol/water (Kow) of tert-butyl cumyl peroxide was then estimated using the slow-stirring method. The Kow test was performed in accordance with the OECD 123 guideline. It was shown that the weighted average value of the 1-octanol/water partition coefficient log10 Pow of the substance is equal to 4.40 ± 0.02 at 25 ± 1 °C which is considered as key value.