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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:
April 20, 2018 - April 27, 2018
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
equivalent or similar to
Guideline:
other: OECD 105 flask method
Deviations:
not applicable
Principles of method if other than guideline:
OECD 105 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:
-4
Temp.:
20 °C
pH:
ca. 4.2

Preliminary visual estimation of the n-octanol solubility

Defined amounts of the test item were stirred with increasing volumes of n-octanol at room temperature and visually checked for any undissolved parts.

Table4: Results of the preliminary visual estimation of the n-octanol solubility

Amount of test item / mg

Added volume of n-octanol / mL

Total volume of n-octanol / mL

Stirring time

/ h

Appearance of mixture

10.5

5

5

~ 0.5

not dissolved

45

50

0.25

not dissolved

150

200

~ 56

not dissolved

According to this preliminary test the solubility of the test item in n-octanol was below 53 mg/L (without correction for the purity).

Calculation of the partition coefficient log POWfrom the preliminary test

The partition coefficient POWmay be estimated from the saturation concentrations in n-octanol and water. The estimated partition coefficient was calculated with the water solubility data determined in project PS20180033.04 (cS = 358 g/L) andthe data obtained above. It was calculated to be: log POW < -3.8.

Due to the calculations the partition coefficient was estimated based on the ratio of the solubilities in water and octanol. The octanol solubility was determined using the flask method.The shake flask method and the HPLC method were not applicable due to the low log POW.

Determination of the solubility in n-octanol: Flask method

The individual saturation solubility of the test item in n-octanol was performed within this study. After that, the partition coefficient was estimated based on the ratio of the test item solubility in n-octanol and water. The flask method was performed as described above. The data for the evaluation are given in Table 5. The n-octanol solubility was calculated from the measured and unrounded concentration values and not from the rounded values given in Table 5.


 Table5: n-Octanol solubility experiments of the test item

Experiment

24 h experiment

48 h experiment

72 h experiment

blank

experiment (72 h)

Amount of test item / mg

16.2

16.9

12.8

--

Amount of octanol / mL

20

20

20

20

Stirring time at 30 °C / h

24

48

72

72

Dilution factor

40

40

40

40

Measured concentration / mg/L

0.65 / 0.68

0.73 / 0.73

0.87 / 0.88

-- / --

Mean concentration / mg/L

0.66

0.73

0.88

--

n-Octanol solubility / mg/L

26.5

29.1

35.1

--

The n-octanol solubilities of the test item showed an increasing tendency, but the individual values were still within the stability criterion of the guideline. As a conservative approach the highest value was stated as final result. The n‑octanol solubility at 20 °C was determined to be 35mg/L.

Calculation of the partition coefficient log POW from the individual solubilities

In project PS20180033.04 the water solubility of the test item at 20 °C was determined to be 358 g/L (± 6 g/L). Within this project the n-octanol solubility of the test item at 20 °C was determined to be 35 mg/L.

The partition coefficient POW of the test item was determined to be: 

log POW = - 4.0

Executive summary:

The partition coefficient (n-octanol/water) of the test item was estimated based on the ratio of the individual solubilities of the test item in water and n-octanol. The solubilities were determined according to the flask method. The shake flask method and the HPLC method were not applicable due to the low log POW.

It was found to be without correction of the purity:

 

log POW = -4.0 

Description of key information

The partition coefficient (n-octanol/water) of the test item was estimated based on the ratio of the individual solubilities of the test item in water and n-octanol. The solubilities were determined according to the flask method.The shake flask method and the HPLC method were not applicable due to the low log POW.

It was found to be without correction of the purity:

 

log POW = -4.0 

Key value for chemical safety assessment

Log Kow (Log Pow):
-4
at the temperature of:
20 °C

Additional information