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Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2013
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Deviations:
no
Principles of method if other than guideline:
Within this study the hydrolytically behaviour of two components of the test item was investigated (main and minor component). As agreed with the sponsor, DEG as second main component of the test item was not taken into consideration.
GLP compliance:
yes (incl. QA statement)
Radiolabelling:
no
Analytical monitoring:
yes
Buffers:
- Buffer pH 4 Citric acid/NaOH/NaCl; Fluka, order no.: 33643
- Buffer pH 7 KH2PO4/Na2HPO4, Fluka, order no.: 33646
- Buffer pH 9 Na2B4O7/HCl, Fluka, order no.: 33648
Details on test conditions:
- Calibration substance
The test item was used for calibration with a stipulated content of 100 %. The calibration was only used to check the system suitability. The hydrolysis tests itself were analyzed using the peak area.

- Preparation of the solutions for calibration
22.7 mg of the test item Ester PSA + DEG were dissolved with acetonitrile / water (1:1) to a volume of 100 ml, resulting in a final concentration of 227 mg/l. This stock solution was used to calibrate the HPLC-system by external standard method applying different injections volumes covering a concentration range from approx. 11 mg/l to 227 mg/l. The chromatogram of the test item showed two peaks corresponding to one main and one minor component. Representative chromatograms of the calibration solutions are given in Figures 5 and 6.

- Preparation of the solution used for verification of the calibration
During the study two different control solutions were used. Dilutions of the test item Ester PSA + DEG in acetonitrile / water (1:1) were prepared resulting in final concentrations of 125 mg/l and 194 mg/l, respectively. These control solutions were used for verification of the calibration before analyzing the test solutions.

- Analysis of the test solutions
The hydrolysis test solutions were analyzed by HPLC at defined time intervals.

- Preparation of the Ester PSA + DEG test solutions
For each pH separate stock solutions were prepared by direct application of approx. 50 mg of the test item to the corresponding buffer systems in 250 ml flasks. Test item concentrations of approx. 200 mg/l were received. Aliquots of the stock solutions were taken without further treatment to obtain individual vials for every test point. Detailed information is provided in paragraph 10, 11, 12 of this report.

- Calculation of hydrolysis
Hydrolysis was observed and calculated using the total peak area values of two peaks of the test item (one main and one minor component) corresponding to the concentrations of Ester PSA + DEG in the test solutions.

- pH determination
The determination was done with a pH-meter equipped with a calibrated single-rod glass electrode.
Duration:
7 d
pH:
7
Temp.:
50
Initial conc. measured:
203.6 mg/L
Duration:
30 d
pH:
4
Temp.:
50
Initial conc. measured:
200.24 mg/L
Duration:
30 d
pH:
9
Temp.:
50
Initial conc. measured:
201.2 mg/L
Transformation products:
no
Details on hydrolysis and appearance of transformation product(s):
The chromatogram of the test item Ester PSA + DEG showed two peaks corresponding to one main and one minor component. Diethylene glycol (DEG) as second main component of the test item cannot be detected by HPLC-UV method. As agreed with the sponsor, it was decided that DEG should not be taken into consideration for the hydrolytically behaviour of the test item within this study. Identification and determination of hydrolysis products for pH 4 and pH 9 was not deemed necessary as the test item was found to be stable at pH 7.
pH:
4
Temp.:
50 °C
Hydrolysis rate constant:
0 s-1
DT50:
353.5 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: Main component
pH:
4
Temp.:
50 °C
Hydrolysis rate constant:
0 s-1
DT50:
12.5 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: Minor component
pH:
9
Temp.:
50 °C
Hydrolysis rate constant:
0 s-1
DT50:
347.1 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: Main component
pH:
9
Temp.:
50 °C
Hydrolysis rate constant:
0 s-1
DT50:
292.3 h
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: Minor component
Validity criteria fulfilled:
yes
Conclusions:
The substance was considered to be stable at 50 °C for pH-value 7. Therefore it can be assumed that the test item is also stable at 25 °C and no half-life times and hydrolysis rates were calculated. For pH 4 and pH 9 abiotic degradation of the test item was observed. Therefore the substance is considered to be hydrolytically unstable at 50°C for pH values 4 and 9.
Executive summary:

The hydrolysis behaviour of the test item was investigated at 50 °C and pH 4, pH 7 and pH 9 over a period of 7 days (pH 7) and 30 days (pH 4 and pH 9) according to OECD TG 111. The stability was monitored by HPLC analysis using UV-detection. Only test tier 1 described in OECD TG 111 was performed because the effect of pH-value is expected to be much more significant than the tests at different temperatures which are much more predictable. The chromatogram of the test item showed two peaks corresponding to one main and one minor component. The test item was considered to be stable at 50 °C for pH-value 7. A slight degradation less than 10 % was observed. Because no degradation was observed, no sterility test was performed in this case. For pH 4 and pH 9 abiotic degradation of the test item was observed. The test item is therefore considered to be hydrolytically unstable at 50°C for pH values 4 and 9. Identification and determination of hydrolysis products for pH 4 and pH 9 was not deemed necessary as the test item was found to be stable at pH 7.

Description of key information

The substance was considered to be stable at 50 °C for pH-value 7. Therefore it can be assumed that the test item is also stable at 25 °C and no half-life times and hydrolysis rates were calculated. For pH 4 and pH 9 abiotic degradation of the test item was observed. Therefore the substance is considered to be hydrolytically unstable at 50°C for pH values 4 and 9 (Neuland, 2013).

Key value for chemical safety assessment

Additional information

Identification and determination of hydrolysis products for pH 4 and pH 9 was not deemed necessary as the test item was found to be stable at pH 7.