Dicalcium pyrophosphate

Water solubility

Link to relevant study record(s)

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

Guideline:

EU Method A.6 (Water Solubility)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

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.