Magnesium bis(dihydrogenorthophosphate)

Water solubility

Link to relevant study record(s)

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.