2-[[4-[ethyl(2-hydroxyethyl)amino]phenyl]azo]-6-methoxy-3-methylbenzothiazolium chloride

Partition coefficient

Link to relevant study record(s)

Reference

Endpoint:

partition coefficient

Type of information:

experimental study

Adequacy of study:

key study

Study period:

October 14, 2016 - November 04, 2016

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Reason / purpose for cross-reference:

reference to other study

Qualifier:

according to guideline

Guideline:

OECD Guideline 107 (Partition Coefficient (n-octanol / water), Shake Flask Method)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method A.8 (Partition Coefficient - Shake Flask Method)

Deviations:

no

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:

-1.6

Temp.:

20 °C

Remarks on result:

other: pH not reported

Preliminary visual estimation of the n-octanol solubility

Defined increasing amounts of the test item were stirred 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	Added volume of n-octanol / mL	Total volume of n-octanol / mL	Concentration of test item / g/L	Stirring time / h	Appearance of mixture
10.0	10.0	10	10	1.0	1	dissolved
10.9	20.9	-	10	2.9	1.5	dissolved
10.7	31.6	-	10	3.2	2	not dissolved (few particles)

According to this preliminary test the solubility of the test item in n-octanol was below 3.2 g/L (without correction for the purity).

Calculation of the partition coefficient log P_OWfrom the preliminary test

The program KOWWIN (part of EPI Suite) was used for calculating the log P_OW of the test item. The calculated value was -0.26. According to the guidance on information requirements and chemical safety assessment, chapter R.7a: endpoint specific guidance, Version 4.1, October 2015, the shake flask method is not suitable. The test item is not a pure substance. For such test items the HPLC method is recommended. Regarding the calculated value the HPLC method is not applicable. Thus 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.

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 saturation solubility c_s in n-octanol and water.

The flask method was performed. The data for the evaluation are given in Table 2. The n-octanol solubility was calculated from the measured and unrounded concentration values and not from the rounded values given in Table 2.

Table 2: 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	792.9	792.2	791.2	--
Amount of octanol / mL	50	50	50	50
Stirring time at 30 °C / h	24	48	72	72
Aliquot of the flasks /mL	0.1	0.1	0.1	0.1
1^stDilution to 100 mL volume / mL	20	20	20	20
Dilution factor	200	200	200	200
Measured concentration / mg/L	6.087 / 6.136	5.818 / 5.806	5.334 / 5.310	-- / --
Mean concentration / mg/L	6.112	5.812	5.322	--
n-Octanol solubility / g/L	1.22	1.16	1.06	--

The n-octanol solubility of the test item at 20 °C was determined to be 1.15 g/L (± 0.08 g/L).

 

Calculation of the partition coefficient log P_OW from the individual solubilities

The water solubility of the test item at 20 °C was determined to be 46 g/L (± 3 g/L). Within this project the n-octanol solubility of the test item at 20 °C was determined to be 1.15 g/L (± 0.08 g/L).

The partition coefficient P_OW of the test item was determined to be: 0.025

log P_OW= -1.6

Final results

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 P_OW = -1.6

Conclusions:

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 = -1.6

Executive summary:

The partition coefficient (n-octanol/water) was determined using the flask method according to OECD 107. As the water solubility was determined to be 46 g/L in an other experiment, only the n-octanol solubility needed to be measured.

The quantity of test item necessary to saturate the desired volume of n-octanol is estimated from the preliminary test. About five times that quantity is weighed into each of three glass vessels fitted with glass stoppers. The batches are stirred for different times at 30 °C (24 h experiment, 48 h experiment, 72 h experiment) in tightly closed flasks.Another experiment is performed according to this procedure but without test item (“blank”). After equilibration (further stirring for 24 h at 20 °C) the suspensions are taken and prepared for the analytical determination via HPLC. The n-octanol solubility of the test item at 20 °C was determined to be 1.15 g/L (± 0.08 g/L). The water solubility of the test item at 20 °C was determined to be 46 g/L (± 3 g/L)in a seperate experimient.

The partition coefficient P_OWof the test item was determined to be: 0.025, wherefore the log P_OW was calculated to be-1.6.

Description of key information

The partition coefficient (n-octanol/water) was determined using the flask method according to OECD 107. As the water solubility was determined to be 46 g/L in an other experiment, only the n-octanol solubility needed to be measured.

The n-octanol solubility of the test item at 20 °C was determined to be 1.15 g/L (± 0.08 g/L). The water solubility of the test item at 20 °C was determined to be 46 g/L (± 3 g/L) in a seperate experimient.

The partition coefficient P_OW of the test item was determined to be: 0.025, wherefore the log P_OW was calculated to be -1.6.

Key value for chemical safety assessment

Log Kow (Log Pow):

-1.6

at the temperature of:

20 °C