Benzoic acid, C12-15-alkyl esters

Water solubility

Link to relevant study record(s)

Reference

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Study period:

July-Sept 2018

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

This is a Klimisch 1 guideline study conducted on the registration substance in accordance with OECD guideline 105 column elution method with a fully validated analytical method.

Qualifier:

according to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of method:

column elution method

Specific details on test material used for the study:

Batch FPIL1807331

Key result

Water solubility:

2.47 µg/L

Conc. based on:

test mat.

Temp.:

20 °C

pH:

ca. 7

Details on results:

Results
The analytical method was successfully validated according to SANCO 3029 rev.4.
With the column elution method a mean average water solubility of 2.47 µg/L at 20°C in deionized water was determined for the test item.

Results of the calibration and validation
During the course of the study two validations were carried out at two different concentrations for the LOQs. For the first test with silica gel as a carrier the LOQ was set at 0.5 µg/L. As the samples showed concentrations below LOQ a second validation was carried out with a LOQ concentration of 0.1 µg/L. Both validations met the requirements given in the SANCO 3029/99 rev. 4 guideline.

Validation results of the analytical method (LOQ= 0.5 µg/L)

Calibration
A representative analysis function for C12-C15 alkyl benzoates with the mass 123 was used to evaluate the results from the silica gel test and the validation at an LOQ of 0.5 µg/L. The function was calculated by quadratic regression analysis using the Excel software. An internal standard (IS) was used and the sum of all peaks was calculated.

Accuracy (Recovery)
The accuracy of the validated method to determine the tested batch of the UVCB substance (C12-C15 alkylbenzoates) is reported as the mean recovery on each fortification level and as the overall mean recovery. The mean recovery figure of 101% complies with the requirements of the guideline and proves the accuracy of the analytical method.

Precision (Repeatability)
The precision of the validated method is reported as the relative standard deviation (RSD) of the repeatability for each fortification level. The repeatability based on 10 determinations is reported as the overall relative standard deviation. The overall mean RSD of 5.6 % proves the repeatability of the described analytical method.

Specificity and Blanks
The GC-MS system used was capable to determine the test item in deionized water using matrix matched calibration. The specificity of the method is shown by chromatograms of an untreated fortification matrix blank.

Calibration
A representative analysis function for C12-C15 alkyl benzoates with the masses 123 used to evaluate the results of this study. The function was calculated by quadratic regression analysis using the Excel software. An internal standard (IS) was used and the sum of all peaks was calculated.

Regression quality
As the calculated coefficient of determination (r²) for C12-C15 alkyl benzoates (UVCB) was close to one, the applicability of the quadratic calibration function was deemed to be acceptable.

Validation results of the analytical method (LOQ=0.1 µg/L)

Accuracy (Recovery)
The accuracy of the validated method to determine the tested batch of the UVCB substance (C12-C15 alkylbenzoates) is reported as the mean recovery on each fortification level and as the overall mean recovery. The mean recovery figure of 104.3% complies with the requirements of the guideline and proves the accuracy of the analytical method.

Precision (Repeatability)
The precision of the validated method is reported as the relative standard deviation (RSD) of the repeatability for each fortification level. The repeatability based on 10 determinations is reported as the overall relative standard deviation. The overall mean RSD of 5.2 % proves the repeatability of the described analytical method.

Specificity and Blanks
The GC-MS system used was capable to determine the test item in deionized water using matrix matched calibration. The specificity of the method is shown by chromatograms of an untreated fortification matrix blank.

Overall Results

Using the column elution method, the water solubility for C12-C15 alkyl benzoates in deionized water was determined to be 2.23 μg/L at 20 °C and a flow rate of 0.5 mL/min and 2.70 μg/L at a flow rate of 0.25 mL/min. The mean average water solubility of the test item is therefore determined to be 2.47 μg/L at 20 °C with an RSD of 10.7 %.

Results were found to meet the required quality criteria with an RSD less than 30 % within one sample batch and between sample batches at different flow rates.

Validation results of the analytical method (LOQ= 0.5 µg/L)

Sample	Fortification level [µg/L]	Conc. MIX [µg/L]	Recovery [%]	Mean Recovery [%]	SD [%]	Recovery RSD [%]
Blank 1	0.00	<LOQ*	n.a.	n.a.	n.a.	n.a.
Blank 2	0.00	<LOQ	n.a.
LOQ 1	0.50	0.497	99.5	103	7.9	7.7
LOQ 2	0.50	0.496	99.2
LOQ 3	0.50	0.498	99.6
LOQ 4	0.50	0.583	117
LOQ 5	0.50	0.491	98.3
10 x LOQ 1	5.00	4.903	98.1	99.3	1.5	1.6
10 x LOQ 2	5.00	4.990	99.8
10 x LOQ 3	5.00	5.089	102
10 x LOQ 4	5.00	4.937	98.7
10 x LOQ 5	5.00	4.907	98.1
			Overall values:	101	5.6	5.6

* The areas found were below 30% of the LOQ.

Validation results of the analytical method (LOQ=0.1 µg/L)

Sample	Fortification level [µg/L]	Conc. MIX [µg/L]	Recovery [%]	Mean Recovery [%]	SD [%]	Recovery RSD [%]
Blank 1	0.00	<LOQ	n.a.	n.a.	n.a.	n.a.
Blank 2	0.00	<LOQ	n.a.
LOQ 1	0.10	0.099	98.8	99.5	2.3	2.3
LOQ 2	0.10	0.097	97.0
LOQ 3	0.10	0.101	101.5
LOQ 4	0.10	0.098	98.0
LOQ 5	0.10	0.102	102.5
10 x LOQ 1	1.00	1.118	111.8	109.1	2.0	1.9
10 x LOQ 2	1.00	1.102	110.2
10 x LOQ 3	1.00	1.086	108.6
10 x LOQ 4	1.00	1.088	108.8
10 x LOQ 5	1.00	1.063	106.3
			Overall values:	104.3	5.5	5.2

* The areas found were below 30% of the LOQ.

The test using silica gel as the carrier and flowrates of 1 and 0.5 mL/min did not lead to any results that fulfilled the requirements of the OECD 105 as the concentration of test item in water was dependent on the flowrate of the water through the column. The lower the flow rate the lower the overall concentration of the 5 consecutive samples in water. Even after long equilibration times of the system this phenomena was observed. See the table below for results.

Results of the water solubility of C₁₂-C₁₅alkyl benzoates with silica gel

Flowrate [mL/min]	Conc. Final Test Item [µg/L]	Mean Conc. Test Item [µg/L]	SD [µg/L]	RSD [%]	Mean Conc. [µg/L]	SD Complete [µg/L]	RSD Complete [%]
1.0	0.551	0.536	0.022	4.05	n.a.	n.a.	n.a.
	0.534
	0.555
	0.500
	0.541
0.5	<LOQ*	<LOQ	n.a.	n.a.
	<LOQ
	<LOQ
	<LOQ
	<LOQ

* The LOQ was set at 0.5 µg/L at the time of analysis

For the above described reason, a different inert support (Florisil) was tested and lead to more repeatable results for which the requirements of the OECD 105 are fulfilled.

 

The below summarizes the concentrations found for five consecutive samples at two different flowrates (0.5 and 0.25 mL/min) for which the mean concentration found is regarded as the water solubility.

Results of the water solubility of C₁₂-C₁₅alkyl benzoates with Florisil

Flowrate [mL/min]	Conc. Final Test Item [µg/L]	Mean Conc. Test Item [µg/L]	SD [µg/L]	RSD [%]	Mean Conc. [µg/L]	SD Complete [µg/L]	RSD Complete [%]
0.50	2.41	2.23	0.105	4.73	2.47	0.263	10.7
	2.24
	2.21
	2.13
	2.17
0.25	2.74	2.70	0.0785	2.91
	2.70
	2.77
	2.74
	2.57

To ensure the quality of the measured results, quality control samples (QC1 and QC2) of the test item were measured alongside the test samples for each measuring time point. Results are regarded as valid if the QC samples are within 85-115% recovery. The table below lists the determined recoveries for the QC samples.

 

Recovery of analyte in QC samples (silica gel)

Sample	Measured	Recovery [%]
QC 1	With samples at 1.0 mL/min flow	92.5
QC 2		94.9
QC 1	With samples at 0.5 mL/min flow	112
QC 2		111

 

Recovery of analyte in QC samples (Florisil)

Sample	Measured	Recovery [%]
QC 1	With samples at 0.50 mL/min flow	97.0
QC 2		103
QC 1	With samples at 0.25 mL/min flow	114
QC 2		101

 

Conclusions:

Using the OECD 105 column elution method, the water solubility for C12-C15 alkyl benzoates in deionized water was determined to be 2.23 μg/L at 20 °C and a flow rate of 0.5 mL/min and 2.70 μg/L at a flow rate of 0.25 mL/min.

Executive summary:

A study was performed at the Fraunhofer Institute for Molecular Biology and Applied Ecology (IME) to determine the water solubility of the UVCB substance C12-C15 alkyl benzoates following OECD guideline 105 (column elution) with a fully validated analytical method.

The mean average water solubility of the test item was determined to be 2.47 μg/L at 20 °C with an RSD of 10.7 %.

Description of key information

Key Study

In 2019, a study was performed at the Fraunhofer Institute for Molecular Biology and Applied Ecology (IME) to determine the water solubility of the UVCB substance C12-C15 alkyl benzoates following OECD guideline 105 (column elution) with a fully validated analytical method. The mean average water solubility of the test item was determined to be 2.47 μg/L at 20 °C with an RSD of 10.7 %.

Supporting Study

In 2009, Chilworth Technology Limited conducted a water solublity study on the registration substance in accordance with OECD 105. The water solubility of the test item was determined to be 0.174 g/L at 30°C.

However, the OECD 105 shake flask method is not appropriate to determine the water solubility of surface active materials. As such, it is possible that the solutions analysed in this study were at concentrations exceeding the critical micelle concentration (CMC) and do not reflect the true solubility of the mono-molecular forms of the substance in water. Evidence of this can be found in comparing the water solubility values determined for shorter C-chain alkyl benzoates (e.g. C9AB and C10AB) as summarised in the read-across justification report in section 13. Furthermore, in 2019 the water solubility of the registration substance was subsequently determined in a high quality experimental study using the more appropriate column elution method in which a value of 2.47 ug/L was obtained. This key study result indicates the solubility of the test substance is approximately a factor of 70,000 -fold lower than determined in this supporting study.

Hence, the result of this study should be taken as indicative bulk solubility of the surface-active substance in water. At a concentration of 0.174 g test item/L in water it is highly likely that micelles or droplets are present as a stable suspension.

Key value for chemical safety assessment

Water solubility:

2.47 µg/L

at the temperature of:

20 °C