Registration Dossier

Administrative data

Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
from August to October 2011
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Guideline study (OECD, EPA, etc)

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2011
Report Date:
2011

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Deviations:
no
GLP compliance:
yes

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
- Name of test material (as cited in study report): XP-7866
- Substance type: White powder
- Physical state: Solid
- Analytical purity: 99.5 % obtained by H1-NMR
- Purity test date: 99.5 %
- Lot/batch No.: 10188-1 JM
- Expiration date of the lot/batch: 28 February 2015
- Storage condition of test material: room temperature in the dark
Specific details on test material used for the study:
Details on properties of test surrogate or analogue material (migrated information):
PHYSICO-CHEMICAL PROPERTIES refers to section 4. physical and chemical properties for details
Radiolabelling:
no

Study design

Analytical monitoring:
yes
Details on sampling:
- PRELIMINARY TEST: sample solutions at pH 4, 7 and 9 were maintained at 50.0 +/- 0.5°C
- Samples:
Duplicate aliquots (A and 8) of sample solution were diluted by a factor of 2 using methanol (pH 4 samples) or 0.025% orthophosphoric acid in methanol (pH 7 and pH 9 samples).
- Standards:
Duplicate standard solutions of test item were prepared in methanol at a nominal concentration of 0.75 mg/l.
- Matrix blanks:
Methanol, pH4 buffer:methanol (1:1 v/v) and buffer (pH 7 or pH 9):0.025% orthophosphoric acid in methanol (1:1 v/v).
- Sampling intervals/times per pH and per temperature:
* pH 4 - 50°C - 0, 72, 144, 192, 240, 312 hours
* pH 4 - 60°C - 0, 24, 48, 72, 96, 168, 216 hours
* pH4 - 70°C - 0, 6, 24, 30, 48, 72, 96 hours
* pH 7 - 15°C - 0, 6, 24, 30, 48, 96, 168 hours
* pH 7 - 25°C - 0, 1, 2, 3, 4, 6, 24, 48 hours
* pH 7 - 35°C - 0, 1, 3, 6, 24, 27, 30 hours
* pH 9 - 5°C - 0, 1, 2, 3 1/2, 5, 6, 22 3/4 hours
* pH 9 - 15°C - 0, 1/4, 1/2, 3/4, 1, 1 1/2, 2 hours
* pH 9 - 5°C - 0, 1/4, 1/2, 3/4, 1, 1 1/2, 2 hours
Buffers:
Buffer solutions:
* pH 4:
- Citric acid: 6.1 mmol dm-3
- Sodium chloride: 4.4 mmol dm-3
- Sodium hydroxide 6.8 mmol dm-3
* pH 7:
- Disodium hydrogen orthophosphate (anhydrous): 3 mmol dm-3
- Potassium dihydrogen orthophosphate: 2 mmol dm-3
- Sodium chloride: 2 mmol dm-3
* pH 9:
- Disodium tetraborate: 1 mmol dm-3
- Sodium chloride: 2 mmol dm-3
NOTE: The buffer solutions were filtered through a 0.2 µm membrane filter to ensure they were sterile before commencement of the test. Also these solutions were subjected to ultrasonication and degassing with nitrogen to minimise dissolved oxygen content.
Details on test conditions:
No details in the report provided. Howver, it is stated in the report that the hydrolysis as a function of Ph has been carried out usingthe method 111 of the OECD Guidelines for testing of Chemicals, 13 April 2004.
Negative controls:
yes
Remarks:
methanol
Statistical methods:
- Sample solution concentration
The mean peak area of each standard was corrected to a nominal concentration of 0.75 mg/l and the mean value taken.
The concentration of the sample solutions (g/l) was calculated as followed:

Cspl =Pspl/Pstd x C std x D x1/1000

where:
Cspl = sample concentration (g/l)
Pspl = mean peak area of sample solution
Pstd = mean peak area of standard solution, corrected to nominal standard concentration
Cstd = nominal standard concentration (0.75 mg/l)
D = sample dilution factor (2)

- Estimation of half-life
From the graph of log10 concentration (gIl) versus time, the rate constant was calculated as followed:

Kobs = - slope x 2.303

where:
Kobs = rate constant (hours-1)

- The rate constant at 25°C was calculated from the Arrhenius plot by taking the anti-log of the result obtained using:
y = A + B.x

where:
y = natural logarithm of the rate constant (hours-1) at 25°C
A = intercept of the Arrhenius plot
B = slope of the Arrhenius plot
x = reciprocal of temperature (25°C) in K (3.354 x 10-3)

- The half-life was obtained from the rate constant using the following equation:
t 1/2 = 0.693/Kobs

where:
Kobs = rate constant (hours-1)
t 1/2 = half-life (hours)

Results and discussion

Preliminary study:
The test was initially performed at 50°C but provided no useful hydrolysis rate data due to either the test item hydrolysing too rapidly during the test and/or hydrolysing while awaiting analysis.
Although, the test item was assessed to have hydrolysed greater than 10% after 5 days indicating tier 2 testing was required and which test temperatures were
applicable. Also, there were several analytical changes to address the issues as follows: The pH 7 and pH 9 samples were diluted with acidified methanol to stabilise them during analysis due to the rapid rates of hydrolysis. At the pH they were adjusted to, and for pH 4, the samples were seen to be stable for at least the analysis period.

Test performance:
The linearity of the detector response with respect to concentration was assessed over the nominal concentration range of 0 to 0.15 mg/I in methanol:water (1: 1 v/v) with an 100 µl injection. This was satisfactory with a correlation coefficient of 0.998 being obtained.
Transformation products:
not measured
Details on hydrolysis and appearance of transformation product(s):
The standards were prepared in methanol as the test item was shown to be stable in this solvent in excess of 7 days. An initial stock was prepared at approximately 15 mgtl in methanol and filtered (0.45 µm PTFE) to remove any undissolved particles. The filtered stock was diluted with methanol in duplicate to 0.75 mg/l; these were stored at room temperature in the dark for continued use. These standards were 10 times more concentrated than the nominal starting sample concentration as a 10 times smaller injection volume was used. This was because a 100 µI injection of a solution in 100% methanol gave very poor peak shape.

The hydrolysis test does not need reference markers of exact concentration, but more a consistent reference point to monitor the level on sample remaining at various time points, hence, the same standards were stored and re-used.
No significant peaks were observed at the approximate retention time of the test item on analysis of any matrix blank solutions.
The kinetics of the study have been determined to be consistent with that of a pseudofirst order reaction as the graphs of log10 concentration versus time are straight lines. It has been observed that the rate of hydrolysis increases with an increase in pH.

Any other information on results incl. tables

* pH 4 at 50°C

Slope = -1.808 x 10-3

kobs = 4.16 x 10-3 hour-1 = 1.16 x 10-6 second-1

t 1/2 = 167 hours

* pH 4 at 60°C

Slope = -4.01 x 10-3

kobs = 9.24 x 10-3 hour-1 = 2.57 x 10-6 second-1

t1/2 = 75.0 hours

* pH 4 at 70°C

Slope = -7.57 x 10-3

kobs = 1.74 x 10-2 hour-1 = 4.84 x 10-6 second-1

t1/2, = 39.7 hours

* pH7 at 15°C

Slope = -3.27 x 10-3

kobs = 7.53 X 10-3 hour-1 = 2.09 X 10-6 second-1

t1/2 = 92.0 hours

* pH 7 at 25°C

Slope = -1.29 x 10-2

kobs = 2.98 x 10-2 hour-1 = 8.27 x 10-6 second-1

t1/2 = 23.3 hours

* pH 7 at 35°C

Slope = -3.62 x 10-2

kobS = 8.33 x 10-2 hour-1 = 2.32 x 10-5 second-1

t1/2 = 8.32 hours

* pH 9 at 5°C

Slope = -6.54 x 10-2

kobs = 0.150 hour-1 = 4.18 x 10-5 second-1

t1/2 = 4.61 hours

* pH 9 at 15°C

Slope = -0.222

kobs = 0.510 hour-1 = 1.42 x 10-4 second-1

t1/2 = 1.36 hours

* pH 9 at 25°C

Slope = -0.726

kobs = 1.67 hour-1 = 4.65 x 10-4 second-1

t1/2 = 0.415 hours

Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Conclusions:
It has been observed that the rate of hydrolysis increases with an increase in pH.
The rate constant and estimated half-life at 25°C of the test item are:
* pH 4: 1.50 x 10-7 second-1 (Rate constant), 53.5 days (Estimated half-life at 25°C)
* pH 7: 7.57 x 10-6 second-1 (Rate constant), 25.4 hours (Estimated half-life at 25°C)
* pH 9: 4.61 x 10-4 second-1 (Rate constant),0.418 hours (Estimated half-life at 25°C)