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Physical & Chemical properties

Water solubility

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Reference
Endpoint:
water solubility
Type of information:
experimental study
Adequacy of study:
key study
Study period:
12 Oct - 19 Dec 2009
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP - Guideline study
Qualifier:
according to
Guideline:
EU Method A.6 (Water Solubility)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Type of method:
flask method
Water solubility:
< 0.255 mg/L
Temp.:
20 °C
pH:
6.3 - 6.5
Details on results:
Please see section Any other information on results incl. tables.

Results

Preliminary test

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

Table 4

Solution

Mean peak area

Standard 30.3 mg/l

4.693

Standard 30.1 mg/l

4.729

Sample 1

0.105

Standard 30.1 mg/l

4.237

Standard 30.7 mg/l

4.469

Sample 2A

0.496

Sample 2B

0.486

Sample 3A

0.103

Sample 3B

0.109

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

Table 5

Sample Number

Time shaken at

~ 30 ºC (hours)

Time equilibrated at 20 ºC (hours)

Concentration (g/l)

Solution pH

1

25 ¾

25 ¼

1.97 x 10-3

7.2

2

24

25 ½

≤9.99 x 10-3

4.2

3

24

25 ½

2.16 x 10-3

8.8

 


Definitive test

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

Table 6

Solution

Mean peak area

Standard 30.2 mg/l

4.482

Standard 30.0 mg/l

4.435

Sample 4A

<1.30 x 10-2

Sample 4B

<1.30 x 10-2

Sample 5A

<1.30 x 10-2

Sample 5B

<1.30 x 10-2

Sample 6A

0.189

Sample 6B

0.192

Standard 30.2 mg/l

4.538

Standard 30.0 mg/l

4.441

Sample 7A

<1.30 x 10-2

Sample 7B

<1.30 x 10-2

Sample 8A

<1.30 x 10-2

Sample 8B

<1.30 x 10-2

Sample 9A

<1.30 x 10-2

Sample 9B

<1.30 x 10-2

Standard 31.8 mg/l

4.432

Standard 15.1 mg/l*

2.012

Sample 10A

2.15 x 10-2

Sample 10B

1.86 x 10-2

 

* See Discussion in Overall remarks and attachments section

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

Table 7

Sample Number

Time shaken at

~ 30 ºC (hours)

Time equilibrated at 20 ºC (hours)

Concentration (g/l)

Solution pH

4

72

24 [10 ºC]

<2.56 x 10-4

6.3

5

72

24 [30 ºC]

<2.56 x 10-4

6.3

6

72

24

3.75 x 10-3

4.2

7

72

24

<2.55 x 10-4

6.3

8

48

24

<2.55 x 10-4

6.5

9

24

24

<2.55 x 10-4

6.5

10

72

24½

4.29 x 10-4

8.9

Mean unbuffered water result (at 20.0 ± 0.5°C): <2.55 x 10-4g/l.

Validation

The linearity of the detector response with respect to concentration was assessed over the nominal concentration range of 0 to 125 mg/l*. * as the pyrophosphate anion. This was satisfactory with a correlation coefficient of 1.000 being obtained. This work was performed as part of Harlan Laboratories Ltd Project Number 2920/0050.


Conclusions:
Interpretation of results (migrated information): slightly soluble (0.1-100 mg/L)
The water solubility of the test material has been determined to be less than 2.55 x 10-4 g/l of solution at 20.0 ± 0.5°C.
The initial solution pH was shown to significantly influence solubility of the test material. When using an identical initial saturation period of 72 hours, the use of the pH 4 buffer solution significantly increased the resulting equivalent test material concentration dissolved (when compared to unbuffered water) to 3.75 x 10-3 g/l at 20.0 ± 0.5°C (at a final solution pH of 4.2), whereas the use of the pH 9 buffer solution increased the resulting equivalent test material concentration to 4.29 x 10-4 g/l at 20.0 ± 0.5°C (at a final solution pH of 8.9). Therefore, although the maximum observed solubility was
3.75 x 10-3 g/l (at a final solution pH of 4.2), the water solubility of the test material may increase further in cases where additional buffering capacity exists.
Executive summary:

Method

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

Conclusion

The water solubility of the test material has been determined to be less than 2.55 x 10-4 g/l of solution at 20.0±0.5°C.

The initial solution pH was shown to significantly influence solubility of the test material. When using an identical initial saturation period of 72 hours, the use of the pH 4 buffer solution significantly increased the resulting equivalent test material concentration dissolved (when compared to unbuffered water) to 3.75 x 10-3g/l at 20.0±0.5°C (at a final solution pH of 4.2), whereas the use of the pH 9 buffer solution increased the resulting equivalent test material concentration to 4.29 x 10-4g/l at 20.0±0.5°C (at a final solution pH of 8.9). Therefore, although the maximum observed solubility was
3.75 x 10-3g/l (at a final solution pH of 4.2), the water solubility of the test material may increase further in cases where additional buffering capacity exists.

Description of key information

Water solubility: < 0.255 mg/L at 20.0 ± 0.5°C (EU Method A.6, GLP)

Key value for chemical safety assessment

Water solubility:
0.255 mg/L
at the temperature of:
20 °C

Additional information

The water solubility of dicalcium pyrophosphate was determined using the flask method in a study conducted according to EU Method A.6 under GLP conditions (Walker and O’Connor, 2010). The water solubility of the test material was determined to be less than 0.255 mg/L at 20 ± 0.5 °C (final solution pH 6.3-6.5).

The initial solution pH was shown to significantly influence solubility of the test material. When using an identical initial saturation period of 72 hours, the use of the pH 4 buffer solution significantly increased the resulting equivalent test material concentration dissolved (when compared to unbuffered water) to 3.75 mg/L at 20.0 ± 0.5°C (at a final solution pH of 4.2), whereas the use of the pH 9 buffer solution increased the resulting equivalent test material concentration to 0.429 mg/L at 20.0 ± 0.5°C (at a final solution pH of 8.9). Therefore, although the maximum observed solubility was 3.75 mg/L (at a final solution pH of 4.2), the water solubility of the test material may increase further in cases where additional buffering capacity exists.