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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:
Testing was conducted between 30 September 2009 and 02 December 2009.
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
EU Method A.6 (Water Solubility)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Remarks:
Date of inspection: 15 September 2009 Date of Signature: 26 November 2009
Type of method:
flask method
Water solubility:
>= 221 g/L
Temp.:
20 °C
Remarks on result:
other: pH was depedent upon the loading rate of the test material.
Details on results:
Please see section Remarks on results including tables and figures.

Results

Preliminary test

 

The preliminary estimate of water solubility was 3.33 g/l of solution.

 

Definitive test

 

The mean peak areas relating to the standard and sample solutions are shown in the following table:

 

Table 9

Solution

Mean peak area

Standard 30.0 mg/l

3.771

Standard 30.6 mg/l

3.924

Sample 7A

2.034

Sample 7B

2.043

Sample 6A

2.071

Sample 6B

2.060

Sample 1A

2.012

Sample 1B

1.993

Standard 30.0 mg/l

3.773

Standard 30.6 mg/l

3.921

Sample 3A

2.001

Sample 3B

2.019

Sample 2A

1.954

Sample 2B

1.989

Standard 30.0 mg/l

3.762

Standard 30.6 mg/l

3.891

Sample 4A

2.142

Sample 4B

2.147

Sample 5A

1.982

Sample 5B

1.994

 

 

 

Test for loading rate dependency

 

The mean peak areas relating to the standard and sample solutions are shown in the following table:

 

Table 10.

 

Solution

Mean peak area

Standard 47.1 mg/l

6.037

Standard 47.2 mg/l

5.959

Sample 8A

6.721

Sample 8B

6.087

Sample 9A

6.690

Sample 9B

5.116

Sample 10A

6.750

Sample 10B

6.718

Standard 47.1 mg/l

6.092

Standard 47.2 mg/l

6.013

Sample 11A

6.746

Sample 11B

6.664

Sample 12A

6.637

Sample 12B

6.390

Sample 13A

6.527

Sample 13B

6.406

Sample 14A

6.208

Sample 14B

6.349

 

 

Additional testing

 

The mean peak areas relating to the standard and sample solutions are shown in the following table:

 

Table 11.

 

Solution

Mean peak area

Standard 30.8 mg/l

3.899

Standard 30.7 mg/l

3.902

Sample 15A1

1.970

Sample 15B1

2.013

Sample 16A1

3.744

Sample 16B1

3.724

Standard 30.8 mg/l

3.910

Standard 30.7 mg/l

3.912

Sample 17A1

1.283

Sample 17B1

1.313

Sample 18A1

2.444

Sample 18B1

2.445

 

 

Overall results for the definitive test, the test for loading rate dependency and the additional testing

 

The concentration (g/l) of test material in the sample solutions is shown in the following table:

 

Table 12.

 

Nominal loading rate (g/l)

Sample Number

Time shaken at

~ 30ºC (hours)

Time equilibrated at 20ºC (hours)

Concentration (g/l)

Solution pH

5.0

1

72

24

3.62

5.5

6

48

24

3.74

5.2

7

24

24

3.69

5.7

2

72

24 [30°C]

3.57

5.4

3

72

24 [10°C]

3.64

5.5

4

72

24

3.90

4.9

5

72

24

3.62

5.7

16.7

8

72

24

11.6

4.5

13

48

24

11.6

5.2

14

24

24

11.2

5.2

9

72

24 [30°C]

10.7

4.6

10

72

24 [10°C]

12.2

4.6

11

72

24

12.1

4.9

12

72

24

11.7

5.3

50

15

72

24

36.1

3.9

100

16

72

24

67.6

3.7

200

17

72

24

117

3.4

400

18

72

24

221

3.0

 

The relationship between nominal loading concentration (g/l) and the resulting analysed equivalent test material concentration (g/l), for the un-buffered water samples, is shown in Figure 5.1. (attached).

 

The water solubility of the test material has been determined to be at least 221 g/l, although observed solubility was extremely sensitive to loading rate.

 

 

Validation

 The linearity of the detector response with respect to concentration was assessed over the nominal concentration range of 0 to 100 mg/l*. This was satisfactory with a correlation coefficient of 1.000 being obtained. This work was performed under Harlan Laboratories Ltd Project Number 2920/0020.

 

 

Discussion

 Even though excess undissolved test material was observed in all of the samples prepared as part of the definitive test, a decision was made to carry out a test for loading rate dependency at a higher loading rate; this was done since loading rate dependency was suspected. Subsequently, the results for this test confirmed loading rate dependency; therefore, it was decided to carry out additional testing at much higher loading rates.

No significant peaks were observed at the approximate retention time of the test material on analysis of any blank solutions.

All peaks observed in the relevant matrix blank chromatograms were also observed in the sample chromatograms. Any additional peaks in the samples, other than the analyte peak, were considered to be most likely due to water-soluble (ionic) impurities in the test material.

The use of sub-micron filtration was sometimes necessary to yield clear sample solutions which were visually free from undissolved test material. However, the use of filtration was determined to have a negligible effect on the concentration of test material in filtered solutions compared to unfiltered solutions. This work was performed under Harlan Laboratories Ltd Project Number 2920/0020.

The ion chromatography method applied directly quantified the dissolved phosphate content of each sample solution and these have been corrected to equivalent test material concentrations based on the theoretical phosphate content of the test material.

Conclusions:
Interpretation of results (migrated information): very soluble (> 10000 mg/L)
The water solubility of the test material has been determined to be at least 221 g/l of solution at 20.0 ± 0.5°C, using the flask method, Method A6 Water Solubility of Commission Regulation (EC) No 440/2008 of 30 May 2008. However, the solubility of the test material was demonstrated to be extremely sensitive to the nominal loading rate of the solution, as demonstrated by the results in the following table:

Nominal loading rate (g/l) Equivalent test material concentration (g/l) Typical solution pH
5.0 3.68 5.2 to 5.7
16.7 11.5 4.5 to 5.2
50 36.1 3.9
100 67.6 3.7
200 117 3.4
400 221 3.0

Investigation into the influence of the pH range 4 to 9 on the solubility of the test material was performed, but in each case the test material demonstrated acidic characteristics on dissolution, overwhelming the capacity of the buffer solutions to give solution pH’s approximately equal to those observed using un-buffered water. Therefore, as the buffering capacity of the solutions used was considered to exceed that of the environment, the solubility of the test material was considered to be independent of the initial pH range 4 to 9, resulting in a consistent acidic solution capable of overwhelming any weak to moderate buffering capacities present.
Finally, although a definitive value for water solubility could not be determined, testing carried out did indicate that the influence of temperature on the observed solubility was not significant.


This study is considered to be adequate and reliable for the purpose of registration under REACH (Regulation (EC) No. 1907/2006).
Executive summary:

Method

The determination was carried out using the flask method, Method A6 Water Solubility ofCommissionRegulation (EC) No 440/2008 of 30 May 2008.

Conclusion

The water solubility of the test material has been determined to be in the range4.18 x 10-2to 4.89 x 10-2g/l of solution at 20.0 ± 0.5°C,using the flaskthod, Method A6 Water Solubility of Commission Regulation (EC) No 440/2008 of 30 May 2008.

The effect of temperature over the range 10 to 30°C has been considered not to have had a significant influence on the solubility of the test material (range 3.72 x 10-2to 4.89 x 10-2g/l).

An assessment of the solubility of the test material over the environmentally relevant pH range of 4 to 9 gave similar solubility results at a solution pH in the range 8.2 to 9.1; however, at a solution pH of 7.2, the water solubility of the test material was much higher. Thus, the effect of pH has been considered to have had a significant effect on the solubility of the test material.

Description of key information

The water solubility of magnesium bis(dihydrogenorthophosphate) was determined according to EU Method A.6 (Water solubility) and under the conditions of GLP. 

Key value for chemical safety assessment

Water solubility:
221 g/L
at the temperature of:
20 °C

Additional information

The water solubility of the test material has been determined to be at least 221 g/l of solution at 20.0 ± 0.5°C. However, the solubility of the test material was demonstrated to be extremely sensitive to the nominal loading rate of the solution, as demonstrated by the results in the following table:

 

Nominal loading rate (g/l)

Equivalent test material concentration (g/l)

Typical solution pH

5.0

3.68

5.2 to 5.7

16.7

11.5

4.5 to 5.2

50

36.1

3.9

100

67.6

3.7

200

117

3.4

400

221

3.0

 

Investigation into the influence of the pH range 4 to 9 on the solubility of the test material was performed, but in each case the test material demonstrated acidic characteristics on dissolution, overwhelming the capacity of the buffer solutions to give solution pH’s approximately equal to those observed using un-buffered water. Therefore, as the buffering capacity of the solutions used was considered to exceed that of the environment, the solubility of the test material was considered to be independent of the initial pH range 4 to 9, resulting in a consistent acidic solution capable of overwhelming any weak to moderate buffering capacities present.

Finally, although a definitive value for water solubility could not be determined, testing carried out did indicate that the influence of temperature on the observed solubility was not significant.