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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:
March 16, 2018 - March 23, 2018
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
equivalent or similar to
Guideline:
other: OECD 105
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:
-2.9
Temp.:
20 °C
Remarks on result:
other: pH not determined

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 particles.

Table3: 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

7.3

10

10

~2

not dissolved

90

100

~65

not dissolved

(slightly cloudy)

According to this preliminary test the solubility of the test item in n-octanol was below 73 mg/L (without correction for the purity).

Calculation of the partition coefficient log POW from the preliminary test

The partition coefficient PO Wmay 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 PS20180017-4 (cS = 1.85 g/L) and the data obtained above. It was calculated to be: log POW < -1.4.

 Also the program KOWWIN (part of EPI Suite) was used for calculating the log POW of the test item. The calculated value was -1.7.

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 Table4.The n-octanol solubility was calculated from the measured and unrounded concentration values and not from the rounded values given in Table4.

Table4: 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

21.6

21.8

19.8

--

Amount of octanol / mL

50

50

50

50

Stirring time at 30 °C / h

24

48

72

72

Dilution factor

40

40

40

40

Measured concentration / mg/L

0.032 / 0.032

0.050 / 0.051

0.056 / 0.055

≤ 0.013* /≤ 0.013*

Mean concentration / mg/L

0.032

0.050

0.055

≤ 0.013*

n-Octanol solubility / mg/L

1.29

2.01

2.22

≤ 0.51*

Quantification limit for measurement (lowest calibration standard)

As a conservative approach the highest measured value was taken into account for the n-Octanol solubility. The n-octanol solubility of the test item at 20 °C was determined to be 2.22mg/L.

Calculation of the partition coefficient log POW from the individual solubilities

In the project PS20180017-4 the water solubility of the test item at 20 °C was determined to be1.85 g/L (± 0.06 g/L). Within this project the n-octanol solubility of the test item at 20 °C was determined to be2.22 mg/L.

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

log POW = -2.9

Executive summary:

The partition coefficient (n-octanol/water) of the test item Reactive Orange 64 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:

 

log POW =  -2.9

 

Description of key information

The partition coefficient (n-octanol/water) of the test item Reactive Orange 64 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:

 

log POW =  -2.9

 

Key value for chemical safety assessment

Log Kow (Log Pow):
-2.9
at the temperature of:
20 °C

Additional information