Sodium 6-amino-5-[[2-[(ethylphenylamino)sulphonyl]phenyl]azo]-4-hydroxynaphthalene-2-sulphonate

Water solubility

Link to relevant study record(s)

Reference

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Study period:

between June 8, 2018 and February 15, 2019

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Qualifier:

according to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

Version / remarks:

1995

GLP compliance:

yes (incl. QA statement)

Type of method:

flask method

Water solubility:

> 28.2 - < 63.5 g/L

Conc. based on:

test mat.

Remarks on result:

other: preliminary test

Water solubility:

11.87 g/L

Conc. based on:

test mat.

Incubation duration:

72 h

Temp.:

20 °C

pH:

8.9

Water solubility:

13.38 g/L

Conc. based on:

test mat.

Incubation duration:

48 h

Temp.:

20 °C

pH:

9

Water solubility:

34.69 g/L

Conc. based on:

test mat.

Incubation duration:

24 h

Temp.:

20 °C

pH:

9

Details on results:

After stirring and centrifugation the aqueous phases were measured by means of HPLC. The solution of each flask has been measured twice at 20 °C.
The signal of test item in the HPLC after treatment for 72 hours at 30 °C and another 24 hours at 20 °C was not as sharp as in the calibration and the freshly prepared standards.

Results of the flask method
Flask 1a 2a 3a 4a
measured value [mg/l] 23.83 / 23.66 26.45 / 27.06 69.41 / 69.37 -- / --
pH value at 24 °C 8.9 9.0 9.0 6.6
average ws [g/l]* 11.87 13.38 34.69 --
mean value of ws [g/l] 19.98 --
standard deviation [g/l] 12.76 --
relative standard deviation [%] 63.88 --

*considering a dilution factor of 500

The recovery of test item in the liquid aqueous phases was very inconsistent. With a higher stirring time, a lower concentration of test item could be found in water.
To verify the accuracy of the analytical method, freshly prepared standard solutions (prepared with test item) were measured in between the samples of the flask method.

Standard solution
(nominal value [mg/l]) Measured value [mg/l] Repeatability [%]
Ü-1 (29.97) 30.41 101.5
29.30 97.8
30.21 100.8
30.54 101.9
Ü-2 (38.28) 39.85 104.1
38.78 101.3
39.91 104.3
40.03 104.6
The recovery rate of measured standard solutions was in the range from 97.8 % to 104.6 %, which shows a good accuracy of analytical method.
Due to the broad signal of test item in the HPLC and the inconsistent recovery of test item in the small liquid phases, an additional flask was prepared.

Additional flask:
At the beginning, the flask with the same amount of test item and water as in the first main test (32 g in 100 ml water) was stirred at room temperature (27 °C), but after one day, stirring of the jelly like solid was not possible anymore.
Although the liquid phase was very small, it was decanted and measured after five days. Considering the dilution of 0.1 ml of the liquid phase to 50 ml with water, the maximum concentration of the test item should be 0.64 g/l.
The HPLC-measurements resulted in a concentration of 24 mg/l (< 5 %) with a broad signal of the test item, as it was observed in the flasks 1a to 3a.

For answering the question, if the test item might have reacted over the time, 2 UV-spectra were measured by means of the UV/Vis spectrometer, before and after stirring for five days. It can be observed, that the test item seems not to have changed in water.

Second main test
For the second main test, three flasks were prepared with an amount of test item and water, and one flask only with water.
Already after one day stirring at 30 °C the test item was highly viscous, pasty and no liquid phases could be decanted. Thus, no liquid could be centrifuged and analyzed.

Conclusions:

Combining the results of the preliminary test and of the first main test, the water solubility of test item at 20 °C and pH 8.9 to 9.0 can only be estimated to be between 11.9 g/l and 63.5 g/l.

Executive summary:

Method

OECD guideline 105. Flask method was chosen, based on the preliminary test results.

Analytical measurements were done as HPLC-UV, upon validation. Analytical validation was done in terms of specificity, linearity, LOD, LOQ, accuracy and precision

Two main tests were run due inconsistencies.

Results

In the preliminary tests, solubility between 28.2 and 63.5 g/l was found.

In the first main test, a jelly phase formed. In the centrifuged liquid phase, test substance concentration decreases with a higher stirring time, i.e. ca. 34.7, 13.4 and 11.9 mg/l after stirring for 24, 48 and 72 h, respectively, at 30 °C followed by a 24 h stirring at 20 °C..

In the second main test, a jelly viscous phase formed and no liquid phase could be decanted.

Description of key information

Estimate of water solubility based on preliminary test and first main test: 11.9 - 63.5 g/l at 20 °C and pH 8.9 -9.

Key value for chemical safety assessment

Water solubility:

11.9 g/L

at the temperature of:

20 °C

Additional information

Flask method - OECD 105.