Phosphinic acid, aluminum salt (3:1)

Hydrolysis

Administrative data

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

disregarded due to major methodological deficiencies

Study period:

From May 05 to 09, 2008

Reliability:

3 (not reliable)

Rationale for reliability incl. deficiencies:

significant methodological deficiencies

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2008

Report date:

2008

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Test guideline 2

Qualifier:

according to guideline

Guideline:

EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)

GLP compliance:

yes (incl. QA statement)

Remarks:

temporary certificate

Test material

Test material information

Constituent 1

Reference substance name:

-

EC Number:

479-150-8

EC Name:

-

Cas Number:

7784-22-7

Molecular formula:

AlH6O6P3

IUPAC Name:

Phosphinic acid, aluminum salt (3:1)

Test material form:

solid: particulate/powder

Radiolabelling:

no

Study design

Analytical monitoring:

yes

Details on sampling:

At time 0, using volumetric pipettes, a 5 mL aliquot was taken from each test article buffer solution. Then 1.00 mL of reagent mix and 250 µL of concentrated (98 %) sulphuric acid were added, but after 10 minutes of stand-by at room temperature no blue colour was noted. Therefore, the hypophosphite anion gives not the colorimetric reaction specific for phosphate and negligible traces of phosphate ion were contained in the test article.

The remainder of the test article buffer solutions were placed into a mechanical shaker thermostated at 50 °C and after 5 days the whole sampling procedure and treatment was repeated.
In this case a slowly blue colour appearance was recorded.

Buffers:

PREPARATION of the BUFFER SOLUTIONS
- pH 4: 164 mL of CH3COOH 0.2 M (5.75 mL of CH3COOH glacial in 500 mL distilled water) were added to 36 mL of CH3COONa 0.2 M (2.72 g of CH3COONa in 100 mL distilled water).
- pH 7: 3 g of TRIS (hydroxymethyl) aminomethane were dissolved into 200 mL of distilled water, the pH was adjusted with concentrated hydrochloric acid at 7.0 then diluted to 250 mL with distilled water.
- pH 9: 4.5 g of TRIS (hydroxymethyl) aminomethane were dissolved into 200 mL of distilled water, the pH was adjusted with concentrated hydrochloric acid at 9.0 then diluted to 250 mL with distilled water.

These buffery were used in place of those described in the C.7 method to avoid the presence of the phosphate for the analysis of the anionic part and because the borate buffer was unable to solubilized the test article at the concentrations used in the test.

Details on test conditions:

EQUIPMENT
- Technical balance, Mettler PB 3002-L Delta range, testing laboratory code No. 343
- Analytical balance, Mettier AG204, testing laboratory code No. 102
- pH meter Mettler MP125, testing laboratory cade Na. 179
- Thermostated mechanical shaker, testing laboratory code No. 271
- Usual laboratory glassware

PROCEDURES
- Prelirninary Test: a preliminary test is performed at 50 ± 0.5 °C, at the tree pH values of 4.0, 7.0 and 9.0. If this test indicates that 50 % or more of the test article has been hydrolyzed in 2.4 hours at 50 °C, or less than 10 % has been hydrolyzed after five days at each of the three pH values (4.0; 7.0 and 9.0), no further testing is necessary.
- Full Test: the experiment is carried out at 50 ± 0.5 °C. and several samples of each pH solution are analysed at different times in order to cover a suitable range of hydrolysis to test for pseudo¬first order behavior of the reaction.

PRINCIPLE of the METHOD
The production of phosphate was recorded by a visual analysis performed with a specific colorimetric reaction which gives a visible absorbent complex.

PREPARATION of the REAGENTS
- Ammonium molibdate tetrahydrate solution: using the technical balance, 1.5 g of ammonium molybdate tetrahydrate were weighed and dissolved in 50 mL of water analytical grade.
- Sulfuric acid solution: using a graduated pipette, 15.6 ml of sulfuric acid 98 % were diluted in 100 mL of water analytical grade.
- Ascorbic acid solution: using the technical balance, 2.7 g of ascorbic acid were weighed and dissolved in 50 mL of water analytical grade.
- Potassium antimony(III) oxide tartrate hemihydrate solution: using the technical balance, 0.34 g of potassium antimony(lll) oxide tartrate hemihydrate were weighed and dissolved in 250 mL of water analytical grade.
- Preparation of the reagent mix: in a 250 mL flask 20.0 ml of the ammonium molybdate tetrahydrate solution, 50.0 mL of sulfuric acid solution, 20 mL of ascorbic acid solution, and 10 mL of potassium antimony(lll) oxide tartrate hemihydrate solution were transferred.

PREPARATION of the TEST ARTICLE
Taking into account the molecular weight, the 0.01 M concentration suggested by the Official Journal L383 Part C method corresponds to a concentration of 2.22 g/L (2220 mg/L).
Six 100 mL test article buffer solutions, two for each pH, were prepared dissolving 222 mg aliquots of test article, weighed by the analytical balance. The pH of the resulting suspensions was measured by a pH meter and adjusted to the correspondent value adding sodium hydroxide 0.1 M dropwise.
For all pH buffer solution, a clear test articie soiution was not obtained, but the suspensions were not filtered in order to maintain the equilibrium between solid and Iiquid phases.

PREPARATION of the STOCK SPIKED SOLUTION
A 14364 µg/mL stock standard solution was prepared weighing with the analytical balance 359.1 mg of potassium dihydrogen phosphate reference material into a 25 mL volumetric flask and dissolving to volume with water.

PREPARATION and ANALYSIS of the TEST ARTICLE SPIKED SOLUTIONS
In order to demonstrate that less of 10 % of the test article after 5 days at 50 °C was transformed to phosphate, a suitable spiking was conducted as follows.
A 5 mL aliquot taken from each test article buffer solution was spiked with 100 µL of the stock spiked solution (about 200 µg/mL as phosphate).
A 1:100 dilution of these solutions, using volumetric glassware, was performed to obtain phosphate concentration within the Iinearity range of the colorimetric method (about 2 µg/mL as phosphate).
A 5 mL aliquot of these diluted spiked solutions was treated adding 1.00 mL of reagent mix and 250 µL of concentrated (98 %) sulphuric acid.
After 10 minutes of stand-by at room temperature, a typical blue colour was developed therefore the hypophosphite anion does not interfere with the phosphate colorimetric reaction.

In order to compare the test article buffer solutions after 5 days shaking at 50 °C with the spiked solutions, a similar 1:100 dilution of each test article buffer solution followed by another whole sampling procedure and treatment was conducted, without obtaining blue colour appearance.

Duration of test

Duration:

5 d

Temp.:

50 °C

Initial conc. measured:

ca. 2.22 g/L

Number of replicates:

6 replicates (2 for each buffer)

Results and discussion

Preliminary study:

A preliminary test is performed at 50 ± 0.5 °C at three pH values, 4.0, 7.0 and 9.0.
No significant variations occurred in test article buffer solutions after 5 days at 50 °C and the comparison with the spiked test article solutions evidenced that the degradation to phosphate was negligible. Therefore, according to the guideline in Official Journal L 283 C.7, the full test was not performed for all three pH tested.

Applicant's summary and conclusion

Validity criteria fulfilled:

no

Conclusions:

It can be concluded that there is no formation of phosphate at 50 °C at pH 4, 7 and 9 for 5 days. The study is disregarded because:
- It does not investigate the stability, as it does not measure the possible disappearance of the test substance
- It is well known that at pH > 6.0 aluminium precipitates as hydroxide or other complex
- It is well knwon that hypophosphite ion is a reducing agent that forms phosphite during the reaction. Further transformation of phosphite to phosphate is very slow.

Executive summary:

The aluminium hypophosphite hydrolysis was investigated according to the OECD guideline 111 and according to the EU method C.7.

A preliminary test was performed at 50 ± 0.5 °C, at the tree pH values of 4.0, 7.0 and 9.0. A possible degradation of test article has been considered the oxidation of the anionic part hypophosphite to phosphate, thus the production of phosphate was recorded by a visual analysis performed with a specific colorimetric reaction which gives a visible absorbent complex. In order to demonstrate that less of 10 % of the test article after 5 days at 50 °C was transformed to phosphate, a suitable spiking was conducted. No significant variations occurred in test article buffer solutions after 5 days at 50 °C and the comparison with the spiked test article solutions evidenced that the degradation to phosphate was negligible.

Conclusion

It can be concluded that there is no formation of phosphate at 50 °C at pH 4, 7 and 9 for 5 days and the full test can be avoid for all three pH tested.

Therefore, it is disregarded because:

- It does not investigate the stability, as it does not measure the possible disappearance of the test substance

- It is well known that at pH > 6.0 the Aluminium precipitates as hydroxide or other complex

- It is well knwon that hypophosphite ion is a reducing agent that forms phosphite during the reaction. Further transformation of phosphite to phosphate is very slow.