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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:
August 27, 2010 to September 28, 2010
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
Study conducted in compliance with agreed protocols, with no or minor deviations from standard test guidelines and/or minor methodological deficiencies, which do not affect the quality of the relevant results. The study report was conclusive, done to a valid guideline and the study was conducted under GLP conditions.
Qualifier:
according to
Guideline:
EU Method A.8 (Partition Coefficient)
Qualifier:
according to
Guideline:
OECD Guideline 117 (Partition Coefficient (n-octanol / water), HPLC Method)
GLP compliance:
yes (incl. certificate)
Remarks:
Date of Signature: November 12, 2008
Type of method:
shake-flask method to: flask method
Partition coefficient type:
octanol-water
Analytical method:
gas chromatography
Type:
log Pow
Partition coefficient:
3.2
Temp.:
22 °C
pH:
7.2

Due to the results of the preliminary test, the log PBOWBof Di-tert-butyl peroxide (CAS# 110-05-4) at 22 °C was estimated to be in the range of about 1.4 and 1.9. On sponsor’s request, the shake flask method was chosen to conduct the main test.

 

During the main study, three tests were carried out, each in duplicate, with volume ratios of both solvents of 1:1, 2:1 and 1:2. After equilibration the concentration of the test item was determined in every phase by GC-MS. The results of the individual measurements are summarized in Table 2X. The tabulated values represent rounded results, which were obtained by calculation using the exact raw data. The log PBOWBwas calculated for each of the six vessels and was found to be in the range of 3.14 to –3.27. Details are given in Table 2X.

 

In order to check the analytical work, the mass balance for each vessel was calculated, too, and the recovery of the test item was found to be in the range of 108% to 124%.Details are given in Table 3X. The tabulated results represent rounded-off values obtained by calculations based on the exact raw data.

 

A typical chromatogram of a standard solution of the water matrix is given in attached Figure 1X. A typical chromatogram of a standard solution of the n-octanol matrix is given in attached Figure2X. A typical chromatogram of an aqueous sample solution is given in attached Figure 3 and of a sample solution in n-octanol in attached Figure 4X. A typical GC-MS chromatogram of a blank solution is shown in attached Figure 5X. An example of a calibration curve and the data for test item-standards used for water matrix is given in attached Figure 6 and Table 4 and used for n-octanol matrix is given in attached Figure7 and Table5X. The correlation coefficient rP2P in water was 0.9984 and in n-octanol was 0.9992 (optimum 1.0000). This reflects the linearity of the GC-MS-system within the calibration range of 0.037 µg/mL to 0.615 µg/mL of the test item in water matrix and of 0.308 µg/mL to 2.153 µg/mL of the test item in n-octanol matrix.

Table2       Calculation of the log PBOWB

Sample no.

Concentration of the
test item found

pH of the aqueous
phase

PBOWB

log PBOWB

n-octanol
phase

aqueous

phase

 

[µg/mL]

[µg/mL]

 

 

 

1

850.18

0.62

7.03

1379.937

3.14

2

884.04

0.59

6.77

1506.490

3.18

3

856.29

0.46

7.66

1864.544

3.27

4

0.00

0.61

6.80

n.a.

n.a.

5

831.19

0.51

7.81

1645.284

3.22

6

948.39

0.58

6.82

1648.940

3.22

Mean value (rounded) =

7.15

1609.039

3.20

Standard deviation = ±

 

181.103

0.049

 

n.a. = not available. Sample 4 could not be evaluated because of an injection error.

Table3       Mass Balance for the Determination of the log PBOWB

 

n-Octanol Phase

Aqueous Phase

Mass found

Mass of

 

Sample no.

Volume

Concentration
of test item

Mass of test item

Volume

Concentration
of test item

Mass of test item

of test item in
both phases

test item added

Recovery

 

[mL]

[µg/mL]

[mg]

[mL]

[µg/mL]

[mg]

[mg]

[mg]

[%]

1

15.0

850.18

12.75

30.0

0.62

0.02

12.77

11.50

111

2

884.04

13.26

0.59

0.02

13.28

11.50

116

3

22.5

856.29

19.27

22.5

0.46

0.01

19.28

17.24

112

4

n.a.

n.a.

0.61

0.01

n.a.

17.24

n.a.

5

30.0

831.19

24.94

15.0

0.51

0.01

24.94

22.99

108

6

948.39

28.45

0.58

0.01

28.46

22.99

124

 

n.a. = not available. Sample 4 could not be evaluated because of an injection error.

 

Conclusions:
During this study the Partition Coefficient (n-Octanol / Water) of Di-tert-butyl peroxide (CAS# 110-05-4) was determined and found to be 3.20 at 22 °C (Standard Deviation = ± 0.05) using the shake flask method. The pH in the aqueous phase was 7.2.
Executive summary:

Vessels containing water and n-octanol with volume ratios of 1:1, 2:1 and 1:2 were shaken for 30 minutes at room temperature. Afterwards the samples were centrifuged and equilibrated for another 1 hour at room temperature. After dilution with acetonitrile the concentrations in both phases were determined by a GC-MS method. From the results obtained the n-octanol / water partition coefficient (log PBOWB) of Di-tert-butyl peroxide (CAS# 110-05-4) was calculated to be

 

log PBOWB = 3.20 at 22 °C

Standard Deviation =±0.05

 

The pH in the aqueous phase was 7.2.

Description of key information

Di-tert-butyl peroxide has an octanol-water partition coefficient of log Pow  3.2.

Key value for chemical safety assessment

Log Kow (Log Pow):
3.2
at the temperature of:
22 °C

Additional information

See:110-05-4, Partition coefficient (shake flask method), Elsner 2010, rs.

The partition coefficient was also determined by the HPLC method (Nijenhuis, 2010). In that study, the log Pow was found to be 5.2. The Nijenhuis study has been designated as a supporting study. Although the study was valid (Klimisch 1), the data are inconsistent with the water solubility of 170 mg/l and the two calculated values for the log Kow (3.45 and 1.5).