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Partition coefficient

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Reference
Endpoint:
partition coefficient
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
July 17, 2018 - August 07, 2018
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: OECD 105 flask method
Qualifier:
equivalent or similar to guideline
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:
titration method
Key result
Type:
log Pow
Partition coefficient:
> 3.8
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.

Table1: 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

11.9

10

10

1

not dissolved

190

200

18

not dissolved

According to this preliminary test the solubility of the test item in n-octanol was below 60 mg/L (without correction for the purity).

Calculation of the partition coefficient log POW from the preliminary test

The partition coefficient POW may 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 PS20180221-3 (cS < 1.08 mg/L) and the data obtained above. It was calculated to be: log POW > 1.7.

Also the program KOWWIN (part of EPI Suite) was used for calculating the log POW of the test item. The calculated value was 11.6.

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 solubility of the test item in organic solvents.

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 Table2. The n-octanol solubility was calculated from the measured and unrounded concentration values and not from the rounded values given in Table2.

Table2: 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

33.1

30.1

31.0

--

Amount of octanol / mL

100

100

100

100

Stirring time at 30 °C / h

24

48

72

72

Dilution factor

1

1

1

1

Density of the sample / g/mL

0.825

0.823

0.825

0.824

Measured concentration /

g Cl /100g

0.1

< 0.1

0.1

< 0.1

Mean concentration / g Cl/L

0.83

< 0.82

0.83

< 0.82

n-Octanol solubility / g/L1)

6.5

< 6.5

6.5

--

Remark: 1) Calculated with a content of 12.6 % Cl (w/w) of the test item.

The n-octanol solubility of the test item at 20 °C was determined to be 6.5g/L. This result is higher compared to the preliminary test results, probably due to n-octanol soluble chlorine containing impurities of the test item.

Calculation of the partition coefficient log POW from the individual solubilities

In the project PS20180221-3 the water solubility of the test item at 20 °C was determined to be < 1.08 mg/L. Within this project the n-octanol solubility of the test item at 20 °C was determined to be 6.5 g/L.

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

log POW> 3.8

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.

It was found to be:

log POW > 3.8

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.

It was found to be:

log POW > 3.8

As the test item is insoluble and organic solvents, no feasible quantification method for the dye itself is available. The measurements are based on the TOC measured in both phases. However, not only the test item but also (more) soluble impurities are included in the TOC measurement. Therefore, the partition coefficient of the test item was calculated with KOWWIN v1.68 included in EpiSuite 4.1.

The partition coefficient of Vat Green 13 was calculated to be log Kow = 11.6.

Key value for chemical safety assessment

Log Kow (Log Pow):
11.6
at the temperature of:
25 °C

Additional information