Magnesium diniobate

Water solubility

Link to relevant study record(s)

Reference

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2016-07-22 to 2016-08-29

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

Version / remarks:

1995

Deviations:

yes

Remarks:

see "Principles of method if other than guideline"

Qualifier:

according to guideline

Guideline:

EU Method A.6 (Water Solubility)

Version / remarks:

2008

Deviations:

yes

Remarks:

see "Principles of method if other than guideline"

Principles of method if other than guideline:

The test was performed according to the OECD-Guideline for Testing of Chemicals No. 105, Water Solubility, flask method with the following modifications:
- Two vessels were set up in a parallel design at 20.0 °C, each vessel was sampled several times instead of sampling just one vessel every time or setting up individual vessels that are sampled only once. This modification helps avoiding weighing errors and enables several samplings from two vessels, i.e., solubility measurements from two individual flasks at each defined time point. The avoidance of weighing errors and the repeated sampling from two separate vessel at each time point (as described above) helps generating more accurate and precise test results.
- The study was performed under inert gas (argon) and under exclusion of atmospheric oxygen and carbon dioxide.

GLP compliance:

yes (incl. QA statement)

Remarks:

2016-05-31

Type of method:

flask method

Key result

Water solubility:

< 0.05 mg/L

Conc. based on:

element (dissolved fraction)

Remarks:

Mg and Nb

Loading of aqueous phase:

100 mg/L

Incubation duration:

>= 5 - <= 34 d

Temp.:

20 °C

pH:

> 6.9 - < 7.7

Remarks on result:

other: Results from filtration + centrifugal filtration

Details on results:

Observations
During the study, a white precipitate was observed in vessels containing the test item. After filtration, regardless of the filtration method (i.e. through a 0.2 µm membrane or through a 0.2 µm membrane with subsequent centrifugal filtration), the solution was clear.

Temperature
The mean temperature was 19.6 ± 0.1 °C

Solution pH
The pH of solutions containing the test item ranged from 6.9 to 7.7. The pH of method blanks ranged from 6.3 to 6.5, except for the pH of the solution in vessel 2 after 5 (pH of 7.1), 6 and 7 days (pH of 7.8) days. However, the pH of the method blank in vessel 2 remained relatively stable at 6.3 – 6.6 after 18 days until the end of the test.

Oxygen concentration
During the test, the oxygen concentration in the acrylic glass box was monitored with a MICRO IV oxygen sensor prior and after sampling. Oxygen concentrations (in %) remained at about 0 %.

Turbidity
Since the sampling volume was limited, the turbidity was measured on each sampling date only in samples filtered through a 0.2 µm membrane (additional 10 mL). The turbidity of the respective centrifugal filtered test sample and method blank was only measured on day 5 with 0.02 NTU. The turbidity was recorded for all samples filtered through a 0.2 µm membrane.

Under the conditions of this test (flask method; loadings of 100.004 mg/L and 100.042 mg/L in vessel 1 and 2), a solubility equilibrium could not be observed. The pH of solutions containing the test item ranged from 6.9 to 7.7 during the test. Measured magnesium and niobium concentrations of solutions (after filtration through a 0.2 µm membrane and centrifugal filtration) ranged from 5.05 µg Mg/L to 20.67 µg Mg/L and from 0.0089 µg Nb/L to 0.1762 µg Nb/L during the test, respectively. Slightly higher magnesium and niobium concentrations were measured in solutions filtered only through a 0.2 µm membrane in comparison to concentrations of solutions applied to centrifugal filtration. This may indicate that smaller particles (i.e. < 0.2 µm but > 3 kDa) are present in solutions filtered through a 0.2 µm membrane. Thus, magnesium and niobium concentrations measured in the fraction < 3kDa are operationally defined as “dissolved concentrations”.

Measured Magnesium and Niob concentrations of solutions containing the test item are compiled in the tables below:

Mean Magnesium concentrations: Solutions after filtration through a 0.2 µm membrane and centrifugal filtration

sampling[d]	mean Mg conc. [µg/L]	SD Mg conc. [µg/L]	variation between sampling intervals [%]	mean Mg conc. - background- corrected [µg/L]	SD Mg conc. [µg/L]	variation between sampling intervals - background-corrected [%]
5	27.40	0.14		14.40	0.14
6	32.62	1.55	19.01	18.07	1.55	25.46
7	34.22	0.42	4.93	16.05	0.42	-11.16
18	18.55	n.a.^*	-45.80	5.05	n.a.^*	-68.53
19	21.51	n.a.^*	15.95	8.67	n.a.^*	71.60
20	21.57	0.59	0.28	6.42	0.59	-25.91
32	42.28	1.99	96.07	20.49	1.99	218.99
33	23.95	3.80	-43.35	10.25	3.80	-49.98
34	35.01	1.21	46.14	20.67	1.21	101.72

Mean Magnesium concentrations: Solutions after filtration through a 0.2 µm

sampling[d]	mean Mg conc. [µg/L]	SD Mg conc. [µg/L]	variation between sampling intervals [%]	mean Mg conc. - background- corrected [µg/L]	SD Mg conc. [µg/L]	variation between sampling intervals - background-corrected [%]
5	34.98	0.90		30.35	0.90
6	35.79	0.40	2.34	30.83	0.40	1.61
7	40.62	0.03	13.49	32.07	0.03	4.01
18	44.25	4.31	8.93	40.21	4.31	25.36
19	40.92	0.64	-7.53	36.99	0.64	-7.99
20	40.58	0.52	-0.83	36.74	0.52	-0.68
32	44.97	0.74	10.82	37.45	0.74	1.94
33	44.67	0.43	-0.66	37.30	0.43	-0.41
34	48.86	1.31	9.38	42.49	1.31	13.91

Mean Niob concentrations: Solutions after filtration through a 0.2 µm membrane and centrifugal filtration

sampling [d]	mean Nb conc. [µg/L]	SD Nb conc. [µg/L]	variation between sampling intervals [%]	mean Nb conc. - background- corrected [µg/L]	SD Nb conc. [µg/L]	variation between sampling intervals - background-corrected [%]
5	0.0921	0.0925		0.0856	0.0925
6	0.1813	0.2143	96.74	0.1762	0.2143	105.94
7	0.1135	0.1175	-37.38	0.1026	0.1175	-41.77
18	0.0466	0.0393	-58.99	0.0466	0.0393	-54.63
19	0.1439	0.0260	209.03	0.1429	0.0260	206.94
20	0.0964	0.0517	-33.01	0.0942	0.0517	-34.08
32	0.0184	0.0004	-80.94	0.0184	0.0004	-80.50
33	0.0124	0.0041	-32.33	0.0124	0.0041	-32.33
34	0.0089	0.0012	-28.45	0.0089	0.0012	-28.45

Mean Niob concentrations: Solutions after filtration through a 0.2 µm

sampling [d]	mean Nb conc. [µg/L]	SD Nb conc. [µg/L]	variation between sampling intervals [%]	mean Nb conc. - background- corrected [µg/L]	SD Nb conc. [µg/L]	variation between sampling intervals - background-corrected [%]
5	0.2180	0.2007		0.2149	0.2007
6	0.7780	0.9800	256.93	0.7733	0.9800	259.87
7	0.5426	0.6820	-30.26	0.5383	0.6820	-30.39
18	0.2661	0.2863	-50.95	0.2661	0.2863	-50.56
19	0.6414	0.4219	140.98	0.6398	0.4219	140.38
20	0.5167	0.2797	-19.43	0.5153	0.2797	-19.46
32	0.0742	0.0350	-85.65	0.0742	0.0350	-85.61
33	0.0842	0.0396	13.50	0.0842	0.0396	13.50
34	0.1097	0.0711	30.33	0.1073	0.0711	27.43

Magnesium diniobate solubility:

Based on means of dissolved Mg and Nb concentrations (as measured on day 5, 6, 7, 18, 19, 20, 32, 33, 34) amounting to 13.34 ± 5.95 µg Mg/L and 0.076 ± 0.060 µg Nb/L, the solubility of magnesium diniobate at 20°C is estimated with ≤ 0.022 mg/L.

Turbidity measurements:

Since the sampling volume was limited, the turbidity was measured on each sampling date only in samples filtered through a 0.2 µm membrane (additional 10 mL). The turbidity of the respective centrifugal filtered test sample and method blank was only measured on day 5 with 0.02 NTU.

Turbidity of test solutions containing magnesium diniobate after filtering through a 0.2 µm membrane

stirring time [d]	sample vessel	turbidity [NTU]	sample vessel	turbidity [NTU]
5	1	0.04	2	0.08
6	1	0.06	2	0.05
7	1	0.08	2	0.04
18	1	0.05	2	0.06
19	1	0.08	2	0.05
20	1	0.04	2	0.03
32	1	0.05	2	0.04
33	1	0.06	2	0.06
34	1	0.07	2	0.05

Method validation summary (dilutions with 0.5 M nitric acid)

validation parameter	results	comment
selectivity	Magnesium at the wavelengths of 280.270 nm and 279.553 nm Niobium at isotope 93 in helium and high helium mode to exclude interferences	no matrix effects observed
linearity	applied calibration functions were linear	See Table 4 correlation coefficient ≥ 0.999240
limits of detection (LOD)	Mg: 0.0080 – 0.1524 µg/L Nb: 0.0003 – 0.0012 µg/L	see Table 4
limits of quantification (LOQ)	Mg: 0.0240 – 0.4573 µg/L Nb: 0.0008 – 0.0037 µg/L	see Table 4
method blanks	Mostly >LOQ Measured test concentrations are reported without and with background correction	See section6.6
accuracy and precision	mean recoveries within measurement series for multi element standard XXI: #1 measurement series: Mg (280.270 nm): 97.1 ± 0.1 % (n = 3)	Diluted to 100 µg Mg/L
accuracy and precision	mean recoveries within measurement series for multi element standard XXI: #3 measurement series: Mg (279.553 nm): 102.6 ± 6.6 % (n = 5) #5 measurement series: Mg (279.553 nm): 113.0 ± 0.5 % (n = 4)	Diluted to 10 µg Mg/L
accuracy and precision	mean recoveries within measurement series for recalibration samples: #3 measurement series: Mg (279.553 nm): 102.1 ± 0.8 % (n = 5) #5 measurement series: Mg (279.553 nm): 104.2 ± 0.8 % (n = 5)	Diluted to 100 µg Mg/L
accuracy and precision	mean recoveries within measurement series for recalibration samples: #1 measurement series: Mg (280.270 nm): 101.7 ± 0.6 % (n = 3)	Diluted to 50 µg Mg/L
accuracy and precision,	mean recoveries within measurement series for Nb quality control standard: #2 measurement series: Nb (93): 123.4 ± 21.9 % (n = 4)	Diluted to 5 µg Nb/L*
accuracy and precision	mean recoveries within measurement series for Nb quality control standard: #4 measurement series: Nb (93): 99.5 ± 1.5 % (n = 4)	Diluted to 0.5 µg Nb/L
accuracy and precision	mean recoveries within measurement series for Nb quality control standard: #4 measurement series: Nb (93): 107.9 ± 3.0 % (n = 4)	Diluted to 0.05 µg Nb/L
accuracy and precision	mean recoveries within measurement series recalibration samples: #2 measurement series: Nb (93): 94.1 ± 5.6 % (n = 4)	Diluted to 5 µg Nb/L
accuracy and precision	mean recoveries within measurement series recalibration samples: #2 measurement series: Nb (93): 92.9 ± 10.7 % (n = 4)	Diluted to 0.5 µg Nb/L*
accuracy and precision	mean recoveries within measurement series recalibration samples: #4 measurement series: Nb (93): 105.4 ± 2.6 % (n = 3) #6 measurement series: Nb (93): 97.3 ± 5.5 % (n = 3)	Diluted to 0.1 µg Nb/L
trueness	recovery from fortification of samples: Mg:98.3 – 105.4 % (n = 8) Nb:63.3 - 104.4 % (n = 14)	**

* Two out of the four samples are not within the limits of 100 ± 15 %. Since Nb recovery in 11 out of 14 QA/QC samples in series #2 is satisfactory, Nb analysis in series #2 is valid.

** The recoveries of Nb in three samples (76.0 %, 72.9 %, 63.3 %) are not within the limits of 100 ± 15 %. Since Nb recovery in 11 out of 14 QA/QC samples in series #2 is satisfactory, Nb analysis in series #2 is valid.

Conclusions:

Under the conditions of this test (flask method; loadings of 100 mg/L), a solubility equilibrium could not be observed.The pH of solutions containing the test item ranged from 6.9 to 7.7 during the test. Measured magnesium and niobium concentrations of solutions (after filtration through a 0.2 µm membrane and centrifugal filtration) ranged from 5.05 µg Mg/L to 20.67 µg Mg/L and from 0.0089 µg Nb/L to 0.1762 µg Nb/L during the test, respectively. Based on means of dissolved Mg and Nb concentrations of filtered and centrifugally filtered samples (as measured on day 5, 6, 7, 18, 19, 20, 32, 33, 34) amounting to 13.34 ± 5.95 µg Mg/L and 0.076 ± 0.060 µg Nb/L, the solubility of magnesium diniobate at 20°C is estimated with ≤ 0.022 mg/L.

Description of key information

The water solubility of magnesium diniobate at 20°C is estimated with ≤ 0.022 mg/L.

Additional information

Under the conditions of a study performed by Klawonn, T (2017) (OECD TG 105; flask method; loadings of 100 mg/L), a solubility equilibrium could not be observed. The pH of solutions containing the test item ranged from 6.9 to 7.7 during the test. Measured magnesium and niobium concentrations of solutions (after filtration through a 0.2 µm membrane and centrifugal filtration) ranged from 5.05 µg Mg/L to 20.67 µg Mg/L and from 0.0089 µg Nb/L to 0.1762 µg Nb/L during the test, respectively. Based on means of dissolved Mg and Nb concentrations (as measured on day 5, 6, 7, 18, 19, 20, 32, 33, 34) amounting to 13.34 ± 5.95 µg Mg/L and 0.076 ± 0.060 µg Nb/L, the solubility of magnesium diniobate at 20°C is estimated with ≤ 0.022 mg/L.