REAKTIV-ORANGE DYPR 1410

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

28 October 1998 to 18 November 1998

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)

Deviations:

no

GLP compliance:

yes

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

Method (HPLC)

HPLC equipment: Spectra-Physics SP 8800 with autosampler SP 8875 and Peltier column oven CO 200
Detector: UV/VIS detector Spectra-Physics: Spectra 200 (SC 200)
Column: Material: stainless steel dimensions: 250 x 4,6 mm by Bischcrf (No. 08087A08) using a guard column
stationary phase: Hypersil ODS, 5μm column temperature: 30°C
Mobile Phase: A: NH4H2P04 in water (c=0.005 mole/l)
B: A/acetonitrile 50/50 (v/v)
Gradient:
Time (min) %A % B
0 100 0
13 0 100
18 100 0
25 100 0
Flow rate: 1.0 ml/min
Injected volume: 20 μl
Detection wavelength: 480 nm

Buffers:

pH4: 20.402 g (0.1 mole) potassium hydrogen phthalate were dissolved in 1000 ml distilled water. 4 ml of sodium hydroxide (0.1 mole/I) were added to 500 ml of this solution and filled up to a volume of 1000 ml with distilled water. The solution was adjusted to pH 4.0 with sodium hydroxide or hydrochloric acid. After decocting it was adjusted to pH 4 for each hydrolysis temperature.

pH7: 13.61 g potassium dihydrogen phosphate were dissolved in 1000 ml distilled water. 29.63 ml of sodium hydroxide (1 mole/l) were added to 500 ml of this solution and filled up to a volume of 1000 ml with distilled water. The solution was adjusted to pH 7.0 with sodium hydroxide or hydrochloric acid. After decocting it was adjusted to pH 7 for each hydrolysis temperature.

pH9: 7.46 g of potassium chloride and 6.184 g of boric acid were dissolved in 1000 ml water. 500 ml of this solution were added to 21.3 ml sodium hydroxide (1 mole/I) and filled up to a volume of 1000 ml with water. The solution was adjusted to pH 9.0 with sodium hydroxide or hydrochloric acid. After decocting it was adjusted to pH 9 for each hydrolysis temperature.

Details on test conditions:

Choice of Concentration
The optimal concentration of the test substance required for the analysis is about 144 to 188 mg/l. This value is less than half the solubility in water (project: EO 044-98) and thus satisfies the requirements of the guidelines.

Preparation of Test Samples
Solutions of the test substance were prepared by weighing between 7 and 10 mg of the test substance in a 50 mi volumetric flask and dissolving in the relevant buffer. The resulting solution was subjected immediately to the hydrolysis procedure.

Preparation of the Standards
The calculation standards were freshly prepared by weighing between 7 and 9 mg of the standard test substance in a 50 ml volumetric flask and dissolving in the buffer pH 4 and pH 7.

Hydrolysis Test Procedure
The flask containing the hydrolysis mixture was placed in a thermostatically controlled water bath at the selected temperature for the specified time. Thereafter it was cooled immediately. The pH was controlled. The HPLC analysis of the unhydrolysed test substance (main compound) was performed without any delay.

Duration:

163.75 h

pH:

4

Temp.:

50

Initial conc. measured:

158.2 mg/L

Duration:

89.2 h

pH:

4

Temp.:

60

Initial conc. measured:

169.12 mg/L

Duration:

40.22 h

pH:

4

Temp.:

70

Initial conc. measured:

170.44 mg/L

Duration:

4.43 h

pH:

7

Temp.:

50

Initial conc. measured:

173.2 mg/L

Duration:

25 h

pH:

7

Temp.:

35

Initial conc. measured:

144.08 mg/L

Number of replicates:

One

Positive controls:

no

Negative controls:

no

Statistical methods:

The initial concentrations (c(0)) of the test substance were calculated from the sample weights. The concentrations during the test process (c(t)) were calculated from the HPLC peak areas of the main component using the formula:


c(t)= c(Standard) . Peak Area (Sample) / Peak Area (Standard)

Preliminary study:

The decomposition at pH 9 is higher than 50 % after 2.4 hours at 50°C. Thus the test substance may by be considered hydrolytically instable at pH 9. According to the guideline a half-life period of less than one day under environmental conditions (25°C) may be estimated.
The pretests at pH 4 and at pH 7 indicate that an examination of the hydrolysis kinetics is essential.

Test performance:

The test performed within the required test parameters specified by the guideline.

Transformation products:

not measured

Details on hydrolysis and appearance of transformation product(s):

Not measured.

pH:

4

Temp.:

25 °C

DT50:

65.5 d

pH:

7

Temp.:

25 °C

DT50:

2.7 d

pH:

9

Temp.:

25 °C

DT50:

< 1 d

Remarks on result:

other: Estimated

Details on results:

Test 1
at pH 4 showed a linear relationship between log(c(t)/c(0)) and t (correlation: r = 0.9856)
at pH 7 showed a linear relationship between log(c(t)/c(0)) and t (correlation: r = 1.0000)
showed a hydrolysis kinetics of first order for both pH values. With accordance to the quoted guideline test 3 was performed using test temperatures of 60 °C and 70 °C for pH 4 and 35 °C for pH 7, respectively.

Test 3
at pH 4 and 60°C showed a linear relationship between log(c(t)/c(0)) and t (correlation: r =1.0000).
at pH 4 and 70°C showed a linear relationship between log(c(t)/c(0)) and t (correlation; r = 0.9959).
at pH 7 and 35⁰C showed a linear relationship between fog(c(t)/c(0)) and t (correlation; r = 0.9994).

In order to estimate the half-life period of the test substance at room temperature for pH 4 and/an extrapolation according to the Arrhenius equation was performed for both pH-values

Summary and extrapolation of the results at pH 4

Temperature	t½(by regression)	Experiment
50⁰C	155.26 h	test 1
60⁰C	60.82 h	test 3
70⁰C	30.45 h	test 3
25⁰C	1572 h = 65.5 d	extrapolation

 

 

Summary and extrapolation of the results at pH 7

 

Temperature	t½(by regression)	Experiment
50⁰C	2.99 h	test 1
35⁰C	17.72 h	test 3
25⁰C	64.0 h = 2.7 d	extrapolation

 

Validity criteria fulfilled:

yes

Conclusions:

At pH 4 the half-life period was determined by extrapolating the results of the experiments at 50 ⁰C, 60⁰C and 70 ⁰C to a temperature of 25⁰C. It was found to be 65.5 days.

At pH 7 the half-life period was determined by extrapolating the results of the experiments at 50⁰C and 35 ⁰C to a temperature of 25°C. It was found to be 2.7 days.

At pH s the decomposition is higher than 50 % after 2.4 hours at 50⁰C. Thus the test substance may by be considered hydrolytically instable at pH 9, According to the guideline a half-life period of less than one day under environmental conditions (25°C) may be estimated.

Executive summary:

The objective of this study was the determination of the abiotic degradation of the test substance Reactive Orange DYPR1410 (the main compound), i.e. the determination of the hydrolysis rate as a function of the pH-value according to guideline 92/69/EEC. appendix, C7. Study performed in accordance with the Principles of Good Laboratory Practice (GLP).

 

At pH 4 the half-life period was determined by extrapolating the results of the experiments at 50 ⁰C, 60⁰C and 70 ⁰C to a temperature of 25⁰C. It was found to be 65.5 days.

 

At pH 7 the half-life period was determined by extrapolating the results of the experiments at 50⁰C and 35 ⁰C to a temperature of 25°C. It was found to be 2.7 days.

 

At pH s the decomposition is higher than 50 % after 2.4 hours at 50⁰C. Thus the test substance may by be considered hydrolytically instable at pH 9, According to the guideline a half-life period of less than one day under environmental conditions (25°C) may be estimated.

Description of key information

At pH 7 the half-life period was determined by extrapolating the results of the experiments at 50⁰C and 35 ⁰C to a temperature of 25°C. It was found to be 2.7 days.

Key value for chemical safety assessment

Half-life for hydrolysis:

2.7 d

at the temperature of:

25 °C

Additional information

At pH 4 the half-life period was determined by extrapolating the results of the experiments at 50 ⁰C, 60⁰C and 70 ⁰C to a temperature of 25⁰C. It was found to be 65.5 days.

 

At pH 7 the half-life period was determined by extrapolating the results of the experiments at 50⁰C and 35 ⁰C to a temperature of 25°C. It was found to be 2.7 days.

 

At pH 9 the decomposition is higher than 50 % after 2.4 hours at 50⁰C. Thus the test substance may by be considered hydrolytically instable at pH 9, According to the guideline a half-life period of less than one day under environmental conditions (25°C) may be estimated.