Alkanoic acid and polyoxomolybdate borate alkanoate clusters

Water solubility

Link to relevant study record(s)

Reference

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Study period:

December 19, 2017 – March 05, 2018

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

Deviations:

yes

Remarks:

exclusion of CO2 and O2; two vessels were set up in a parallel design, each vessel was sampled several times instead of sampling one vessel at every point in time.

Qualifier:

according to guideline

Guideline:

EU Method A.6 (Water Solubility)

Deviations:

yes

Remarks:

exclusion of CO2 and O2; two vessels were set up in a parallel design, each vessel was sampled several times instead of sampling one vessel at every point in time.

GLP compliance:

yes (incl. QA statement)

Remarks:

signed 2016-05-31

Type of method:

flask method

Water solubility:

9.34 mg/L

Conc. based on:

element (dissolved fraction)

Temp.:

20.3 °C

pH:

>= 3.8 - <= 4

Remarks on result:

other: dissolved Mo from day 1 until day 3, at aloading of 100 mg test item/L

Water solubility:

84.92 mg/L

Conc. based on:

test mat. (dissolved fraction)

Temp.:

20.3 °C

pH:

>= 3.8 - <= 4

Remarks on result:

other: dissolved test item from day 1 until day 3, at aloading of 100 mg test item/L

Details on results:

Observations
During the test a green / blue not dissolved solid was observed on the sample boats used for introduction of test item in test item loaded vessels. Samples were taken out of the vessels, filtered (0.2 μm PES membrane, DIA Nielsen, Germany). The turbidity was measured in the filtrates to ensure that only dissolved Mo would get measured.

Temperature
The temperature in the thermostatically controlled water bath in the argon filled box was monitored by a thermo data logger (Testo 175-T2. Testo AG. Leutkirch. Germany). The mean temperature was 20.3 ± 0.1 °C.

Solution pH
The pH value of solutions containing the test item was in the range of 3.8 – 4.0. The pH of method blanks remained at 6.2 – 6.4.
The pH was measured on sampling days using a Multi 9630 IDS device from WTW (Weilheim, Germany). Measurements were taken after readings had stabilized and waiting for an additional minute. The pH electrodes (Sentix 940-P) were calibrated every week during the test and checked on each sampling day. Different electrodes for test item loaded vessels and method blanks were used. Calibrations were performed using commercially available pH standards.

Turbidity
The turbidity of filtered samples was measured with a WTW Turb 550 IR (WTW, Weilheim, Germany). The turbidity was always << 1 NTU indicating that only dissolved test item get measured.

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

Dissolved molybdenum concentrations
Method blanks show very low Mo levels. However, these are far below concentrations in actual samples and are due to the low LOD / LOQ.

Method validation summary

validation parameter	results	comment
selectivity	Mo selective measurements: ICP-MS: 97Mo
linearity	applied calibration function was linear	correlation coefficient was 0.99969
limits of detection (LOD)	ICP-MS: 0.004 µg Mo/L
limits of quantification (LOQ)	ICP-MS: 0.12 µg Mo/L
method blanks	0.07 - 0.19 µg Mo/L However, these concentrations were far below concentrations in actual samples (8.55 - 10.06 mg/L)	-
accuracy and precision	mean recovery in CRM TMDA-70.2: ICP-MS: 100.7 ± 1.0 % (n = 4)	132.5 μg/L Mo (dilution 2-fold with 0.5 M nitric acid)
accuracy and precision	mean Mo recovery in quality control standard #23 from LabKings: ICP-MS: 98.2 ± 1.0 % (n = 4)	for concentration range of diluted sDiluted to 50 μg/L Mo with 0.5 M nitric acid
accuracy and precision	mean Mo recovery in quality control standard #23 from LabKings: ICP-MS: 101.3 ± 2.1 % (n = 4)	Diluted to 200 μg/L Mo with 0.5 M nitric acid
accuracy and precision	mean Mo recovery in recalibration samples: ICP-MS: 96.8 ± 0.7 % (n = 4)	Diluted to 100 μg/L Mo with 0.5 M nitric acid
trueness	Mo recoveries in fortified samples: 99.0 – 99.5 % (n = 3)

Results

Molybdenum concentrations remained constant during testing from day 1 to day 3. Dissolved Mo concentrations of samples from two consecutive days did not differ by more than 15 %, and an increasing trend of the variation in concentrations between samplings from day 1 to day 3 was not observed. Thus, the validity criteria as foreseen in OECD 105 and Regulation 440/2008/EC A.6 were met.

The mean dissolved molybdenum concentrations of solutions sampled from day 14 until day 16 were calculated.

Mean dissolved Mo concentrations day 14 – day 16:

Vessel 1: 11.3 ± 0.5 mg Mo/L

Vessel 2: 14.8 ± 0.5 mg Mo/L

The amount of 2 -ethylhexanoic acid, molybdenum salt dissolved was calculated based on the molybdenum content of the test substance as follows:

 = mean of measured Mo concentration * 100 % / 14.9 % [Mo content of test item]

mean calculated 2 -ethylhexanoic acid, molybdenum salt dissolved day 14 – day 16:

Vessel 1: 76.11 ± 3.02 mg/L

Vessel 2: 99.46 ± 3.27 mg/L

Final result: Under the conditions of this test (under exclusion of CO2 and O2, under inert argon gas; flask method; loadings of 100.16 and 100.00 mg/L in vessel 1 and 2, respectively), a solubility equilibrium was reached from day 14 until day 16 of testing. The mean amount of dissolved Mo from day 14 until day 16 at 20.0 ± 1.0 °C is 13.1 ± 1.9 mg/L (determined as dissolved Mo, separated by centrifugation and subsequent filtration from undissolved test item). This corresponds to a calculated water solubility of dissolved 2 -ethylhexanoic acid, molybdenum salt of 87.8 ± 12.6 mg/L, calculated based on a molybdenum content of 14.9 %. Solution pH in method blanks ranged from 5.9 to 7.0, whereas the pH in samples containing the test item decreased to 3.8 - 4.0.

Conclusions:

The water solubility of test item 84.92 ± 1.31 mg/L, calculated based on a molybdenum content of 11.0 %, at a loading of 100 mg/L, 20.3 ± 0.1 °C and pH 3.8 – 4.0.

Description of key information

Under the experimental conditions of the test carried out according to OECD 105 guideline (flask method), the water solubility of the test item was determined to be 84.92 mg/L at 20°C and pH = 3.8 - 4.

Key value for chemical safety assessment

Water solubility:

84.92 mg/L

at the temperature of:

20 °C