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Water solubility

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Reference
Endpoint:
water solubility
Type of information:
experimental study
Adequacy of study:
key study
Study period:
17.-24.10.2019
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 105 (Water Solubility)
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method A.6 (Water Solubility)
Version / remarks:
European Commission Regulation (EC) No. 440/2008 and No. 260/2014
Deviations:
no
GLP compliance:
no
Type of method:
column elution method
Key result
Water solubility:
< 0.23 mg/L
Conc. based on:
test mat.
Temp.:
25 °C
pH:
6.5

Preliminary test

ln a simple preliminary test, mixtures of water and test item are prepared and assessed visually. The approximate water solubility of the test item, resulting from the preliminary test, indicates which of the two methods for the determination of the water solubility is applicable. Whereas the column elution method covers solubilities below 10 mg/L the flask method is suitable for solubilities above 10 mg/L. Additionally, the results of the preliminary test provide information regarding the appropriate amount of test item to be used in the main test.

 

Column elution method

The column elution method is based on the elution of test item with water from a micro-column which is charged with an inert support material, previously coated with an excess of the test item. For the column elution method two micro-columns with different flow rates (approx. 25 ml/h and approx. 12.5 ml/h) are used. Water is pumped with a defined flow rate and transferred by inert tubes to the micro-columns which are fitted with one way stopcocks. After passing the coated column consecutive eluate fractions are collected by a fraction collector. The first five fractions are discarded to remove water soluble impurities. To determine the water solubility of the test item at least five fractions are analysed. The concentrations should be constant within ± 30 % and should not show any increasing or decreasing tendency in five consecutive fractions. If this criterion is fulfilled the run can be stopped. All other fractions will be discarded. For the analysed fractions the pH values, the volumes and the temperatures are measured, too. A coating check at the end of the study is performed to confirm that enough residual test item remained on the columns.

 

Chemicals

• Demineralized water, Roth

• Acetonitrile, Sigma-Aldrich

• Tetrahydrofuran (THF), Sigma-Aldrich

• Sea sand, Merck

 

Apparatus

• Analytical apparatus (refer to chapter 4.4)

• Analytical balance, Sartorius R 200 D

• Analytical balance, Sartorius U 4100 S

• pH-meter, Mettler Seven Easy

• Ultrasonic bath, Sonorex Super RK255H

• Thermostatically controlled columns

• Rotary evaporator with vacuum pump (Fa. Vacuubrand)

• Pipettes, Eppendorf and Brand

• Thermometer No. 1344

 

Any other information on results incl. tables

Sample preparation.

After passing the columns, the concentration of the test item in 5 collected aqueous fractions was determined in duplicate by HPLC. For this purpose, the fractions were diluted from 0. 75 ml to 1 ml with acetonitrile. The eluates of the coating check were diluted from 1.0 ml to 10 ml with acetonitrile and again from 0.05 ml to 1.0 ml with acetonitrile / demineralized water 75:25 (v/v%).

 

Preliminary test

Three preliminary tests were carried out with specified amounts of the test item and 100 ml and 500 ml demineralized water, respectively. After each addition of an amount of water, the mixture was stirred for 24 hours, and visually checked for any undissolved particles.

 

Table: Results of the preliminary test

Amount of test item /mg

Total volume of demineralized water / mL

Appearance of mixture

7.0

100

Not dissolved

13.5

500

Not dissolved

2.4

500

Not dissolved

 

The preliminary test showed that the water solubility of the test item was < 10 mg/I. According to the preliminary test the water solubility was determined by the column elution method in the main test.

 

Column elution method

102.2 mg of the test item were dissolved in 100 ml tetrahydrofuran. For charging the columns in each case 25 ml of the test item solution was added to about 3 g of sea sand and the mixtures were shaken. The solvent was then removed under reduced pressure using a rotary evaporator (40 °C, approx. 10 mbar). The dry residues were placed into the columns of the test apparatus, which have afterwards been filled with water (test temperature: 20 °C; water pH at 23 °C: 6.5). After a swelling time of 2 h pumps were started to rinse the test item coated sand with demineralized water. At the end of the study it was confirmed that residual test item remained on the columns. The residual test item was eluted with 50 ml tetrahydrofuran. As blank value demineralized water was tested. No signal was detected in the range of the retention time of the test item. The concentration of the test item was quantified by HPLC.

 

Column 1:

Rotation period of the fraction collector:          90 min per fraction

Duration of sampling:                           about 48 h (32 fractions)

 

Table column elution method, column 1 (approx. 12.5 mL/h

Fraction no

V / mL

pH

Water solubility / µg/L

22

18.0

6.3

<21.3

23

18.0

6.5

<21.3

24

18.0

6.5

<21.3

25

18.0

6.5

<21.3

26

18.0

6.2

<21.3

 

The water solubility was found to be below the quantification limit of 21.3 μg/L.

 

Column 2:

Rotation period of the fraction collector:          45 min per fraction

Duration of sampling:                           about 48 h (64 fractions)

 

Table column elution method, column 2 (approx. 25.0 mL/h

Fraction no

V / mL

pH

Water solubility / µg/L

48

16.5

6.3

<21.3

49

16.5

6.1

<21.3

50

16.0

6.4

<21.3

51

16.0

6.5

<21.3

52

16.0

6.4

<21.3

 

The water solubility was found to be below the quantification limit of 21.3 μg/L.

 

In both columns the concentration of five consecutive fractions was constant within ± 30 %. No increasing or decreasing tendency was observed.

 

Table Coating check

 

Amount of test item

used for coating /mg

Measured concentration of

 test item in eluate /mg

Amount of test item

 eluated /mg

Column 12.5 mL/h

25.6

2.324/2.326

23.3

Column 25.0 mL/h

25.6

2.038/2.045

20.4

 

The coating check was successful. Enough test item remained on the columns. The water solubility cs of the test item was below the quantification limit of 21.3 μg/L (mean value of the columns) in both columns.

Conclusions:
The water solubility cs of the test item at a temperature of 20°C was determined according to the column elution method. It was found to be below the quantification limit: cs < 0.23 mg/L
Executive summary:

The water solubility was determined according to OECD 105 using the column elution method. The preliminary test showed that the water solubility of the test item is < 10 mg/L. The column elution method showed a solubility below the quantification limit: cs < 0.23 mg/L

Description of key information

The water solubility cs of the test item at a temperature of 20 °C was determined according to the column elution method. lt was found to be below the quantification limit:

cs < 0.23 mg/l

Key value for chemical safety assessment

Additional information

The water solubility was determined according to OECD 105 using the column elution method. The preliminary test showed that the water solubility of the test item is < 10 mg/L. The column elution method showed a solubility below the quantification limit: cs < 0.23 mg/l