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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:
06.09.- 06.12.16
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 107 (Partition Coefficient (n-octanol / water), Shake Flask Method)
Qualifier:
according to guideline
Guideline:
EU Method A.8 (Partition Coefficient - Shake Flask Method)
GLP compliance:
no
Type of method:
flask method
Partition coefficient type:
octanol-water
Analytical method:
high-performance liquid chromatography
Key result
Type:
log Pow
Partition coefficient:
3
Temp.:
23 °C
pH:
> 5.7 - < 6

Preliminary visual estimation of the n-octanol solubility

Increasing amounts of the test item were stirred with a defined volume of n-octanol at room temperature and visually checked for any undissolved parts.

Table 1: Results of the preliminary visual estimation of the n-octanol solubility

 Amount of test item / mg  Total amount of test item / mg  Total volume of n-octanol / ml  Stirring time / min  Appearance of mixture
 18.0  18.0  2  55  dissolved
 81.2  99.2  2  80  dissolved
 228.1  323.3  2  45  dissolved
 874.2  1201.5  2  50  dissolved

According to this preliminary test the solubility of the test item in n-octanol was > 600 g/l (without correction of the purity).

Calculation of the log Pow from the preliminary test: The estimated particion coefficient was calculated with the water solubility of 460 mg/l. It was calculated to be > 3.1.

Also the program KOWWIN (part of EPI Suite) was used for calculating the log Pow of the test item. The calculated value was 3.5.

Therefore according to the guidelines the partition coefficient n-octanol/water of the test item at room temperature was determined by the shake flask method.

Shake flask method

A specified amount (see Table 2) of the test item was dissolved in 100 ml n-octanol (saturated with demineralized water). 10 ml of this solution were added to six different flasks (experiment: 1A, 1B, 2A, 2B, 3A, 3B). Subsequently different amounts of n-octanol (saturated with demineralized water) and 10 ml demineralized water (saturated with n-octanol) were added to the flasks as described in the table. All mixtures were shaken for several minutes at ambient temperature (23 °C). After separation of the phases each phase was centrifuged (30 minutes at 23 °C and 15000 rpm) and the pH values of the aqueous phases were measured. For analytics the samples were prepared as described as before and subsequently the concentrations of the test item in the different phases were determined by HPLC.

 

Table 2: Test conditions and results of the shake flask method

Experiment

1A

1B

2A

2B

3A

3B

Amount of test item

101.5

101.5

101.5

101.5

101.5

101.5

Concentration of the stock solution /mol/l

0.005

0.005

0.005

0.005

0.005

0.005

Volume of added stock solution /ml

10

10

10

10

10

10

Volume of added n-octanol /ml

0

0

10

10

30

30

pH of the aqueous phase at 23°C

6.0

5.7

5.7

5.7

5.7

5.7

Measured concentration in aqueous phase / mg/l

0.61/0.61

0.86/0.87

0.30/0.30

0.49/0.49

0.13/0.14

0.15/0.15

Mean concentration in aqueous phase / mg/l

0.82

1.15

0.40

0.65

0.18

0.21

Measured concentration in n-octanol phase / mg/l

2.50/2.51

2.49/2.48

1.31/1.35

1.26/1.27

0.70/0.74

0.58/0.57

Mean concentration in n-octanol phase / mg/l

1000.2

993.5

532.1

506.1

286.6

229.6

  For the mean concentration the sample preparation (dilution) is taken into account.

The following partition coefficients (Table 3) are calculated from the measured and unrounded concentration values and not from the rounded values given in the Table 2.

 

Table 3: Partition coefficients of the shake flask method at pH 9

Experiment

POW

Log POW

Average Log POW

1A

1225.7

3.09

3.01

1B

862.2

2.94

3.01

2A

1329.7

3.12

3.01

2B

776.1

2.89

3.01

3A

1580.0

3.20

3.12

3B

1117.2

3.05

3.12

Mean value (experiment 1A to 3B)

 

 

3.0

Standard deviation

 

 

0.1

   

The six determined log POWvalues are within a range of ± 0.3 units as requested by the guideline. The partition coefficient POWof the test item was determined to be: log POW= 3.0

 

Conclusions:
The partition coefficient POWof the test item according to the shake flask method was determined to be: log POW= 3.0.
Executive summary:

A study was conducted in accordance with OECD 107 and Regulation (EC) No 440/2008 method A.8 to determine the partition coefficient of the test substance using the shake flask method. The partition coefficient POWis defined as the ratio of the equilibrium concentrations of a dissolved test item in the two-phase system consisting of n-octanol and water. The partition coefficient POWis dimensionless and usually given in the form of its logarithm to base ten. The partition coefficient (n-octanol/water) of the test item was determined at room temperature (23 °C) to be: log POW= 3.0

Description of key information

A study was conducted in accordance with OECD 107 and Regulation (EC) No 440/2008 method A.8 to determine the partition coefficient of the test substance using the shake flask method. The partition coefficient POWis defined as the ratio of the equilibrium concentrations of a dissolved test item in the two-phase system consisting of n-octanol and water. The partition coefficient POWis dimensionless and usually given in the form of its logarithm to base ten. The partition coefficient (n-octanol/water) of the test item was determined at room temperature (23 °C) to be: log POW= 3.0

Key value for chemical safety assessment

Log Kow (Log Pow):
3
at the temperature of:
23 °C

Additional information