tetrasodium 3-amino-4-{[4-({4-fluoro-6-[phenyl(2-{[2-(sulfonatooxy)ethyl]sulfonyl}ethyl)amino]-1,3,5-triazin-2-yl}amino)-2-sulfonatophenyl]diazenyl}-5-hydroxynaphthalene-2,7-disulfonate

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

From Oct. 19, 2004 to Nov. 25, 2004

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Deviations:

no

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

no

Analytical monitoring:

yes

Buffers:

- pH 4:
21.01 g citric acid monohydrate were dissolved in 200 mL sodium hydroxide solution (c = 1 mol/L). This solution was filled up to a volume of 1,000 mL with distilled water. 44 mL of hydrochloric acid (c = 1 mol/L) were added to 560 mL of this solution and filled up to a volume of 1,000 mL with distilled water. The pH value was adjusted to pH 4 for each hydrolysis temperature.
- pH 7:
13.61 g potassium dihydrogen phosphate were dissolved in 1,000 mL distilled water. 30 mL of sodium hydroxide solution (c = 1 mol/L) were added to 500 mL of this solution and filled up to a volume of 1000 mL with distilled water. The pH value was adjusted to pH 7 for each hydrolysis temperature.

- pH 9:
7.46 g potassium chloride and 6.18 g boric acid were dissolved in 1,000 mL distilled water. 21 mL of sodium hydroxide solution (c = 1 mol/L) were added to 500 mL of this solution and filled up to a volume of 1,000 mL with distilled water. The pH value 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 analyses was lower than 10 g/L. This value was less than half of the solubility in water (475.3 g/L without correction for the purity) and less than 0.01 mol/L for the test substance. This complies with the requirements of the guidelines.

Preparation of the Test Samples
Solutions of the homogenized test substance were prepared by weighing between 135 and 188 mg of the test substance in a 25 mL volumetric flask and dissolving the test substance in the relevant buffer. This preparation was done in a glove box filled with nitrogen. The resulting solution was subjected immediately to the hydrolysis procedure.

Hydrolysis Procedure
The flask containing the hydrolysis mixture was placed in a thermostatically controlled water bath at the selected temperature for the specified time. Thereafter an aliquot was taken. The volumetric flask was flooded with nitrogen again. The aliquots were diluted with distilled water (0.1 mL to 1 mL). The pH was controlled and the concentration of the unhydrolysed test substance (main compound) was measured by HPLC.

Preliminary tests
The preliminary tests were done at 50±0.5°C with buffers at pH 4, 7 and 9, for 2.4 h and 5 d.

Test 1 (15.3-47.5 h)
Test 1 was done at 50±0.5°C with the buffer at pH 4 and pH 7. At least 4 aliquots were taken between a decomposition rate of 20 and 70%. Due to the fact that test 1 for pH 4 and pH 7 at 50°C clearly showed a pseudo first order reaction, no test 2 but test 3 had to be performed.

Test 3
Test 3 was done at 55 and 65 ± 0.5 °C with the buffer at pH 4 and at 35±0.5 °C with the buffer at pH 7. At least 3 aliquots were taken at the beginning of the experiment and at least two aliquots with a decomposition rate higher than 30%.

Preparation of Standard Solution
The standards for calibration and recheck were freshly prepared.

Calculations
The concentration of the standard and the initial concentration Co of the test substance were calculated from the sample weights. The concentration during the test process Ct was calculated from the HPLC software. Each concentration during the test process was measured twice. In the case of pseudo first order reaction, according to the following relationships a linear dependence on the time (t) is expected for log (Ct/Co): log (Ct/Co) = t * (-Kobs)/2.303.
The experimental data of Test 1 were checked graphically for the approximate fulfilment of this relationship. The constant Kobs was determined by linear regression of –log (Ct/Co) to t.
The half-life period t1/2, was calculated according to: t1/2, = In2/Kobs
The same calculation was done for test 3.
The Arrhenius-equation was used to extrapolate the rate constants at higher temperature to room temperature: In k25"c = - E/R * 1/298.2 + constant
The constant "E/R" and "constant." were determined by linear regression of 1/T to In Kobs
The concentrations were quantified by comparing integrated peak areas with a calibration (external standard method). The solutions were determined by HPLC. The integration and calculation of the concentration was automatically carried out using the HPLC System Agilent 1100 series. The standards were prepared by dissolving the test substance in distilled water and diluted with distilled water.
The detector linearity was checked (calibration).
Calibration: y=mx+b
X= Amount (mg/L); y=Area; m=8.091, b=-90.61; correlation: 0.99936

Positive controls:

no

Negative controls:

no

Transformation products:

not measured

Key result

pH:

4

Temp.:

25 °C

DT50:

14.8 d

Type:

(pseudo-)first order (= half-life)

Key result

pH:

7

Temp.:

25 °C

DT50:

12.5 d

Type:

(pseudo-)first order (= half-life)

Key result

pH:

9

Temp.:

25 °C

DT50:

< 12 h

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: instable based on preliminary test

Details on results:

- At pH 4 the half-life period was determined by extrapolation of the results of the experiments at 50°C, 55°C and 65°C to a temperature of 25°C. It was found to be 14.8 d.
- At pH 7 the half-life period was determined by extrapolation of the results of the experiments at 50°C and 35°C to a temperature of 25°C. It was found to be 12.5 d.
- In the preliminary study, at pH 9 more than 50% of the reaction was observed after 2.4 h at 50°C (t1/2< 1 d). Thus the test substance was considered hydrolytically unstable and according to the guidelines no additional testing was required at this pH.

Results of the Preliminary Test

Table.1: Test at pH 4, 7 and 9 and 50°C

pH	Duration	C0in mg/L	Ctmg/L	Ct/ C0	Decomposition in %
4	2.4 h	6491	6063	0.9340	6.6
	2.4 h	7395	6861	0.9278	7.2
4	5 d	7460	614.6	0.0824	91.8
	5 d	5910	489.8	0.0829	91.7
7	2.4 h	5912	4751	0.8036	19.6
	2.4 h	6488	5226	0.8054	19.5
9	2.4 h	6356	<414	<0.065	>93
	2.4 h	6246	<414	<0.066	>93

 

The decomposition at pH 9 was higher than 50% after 2.4 h at 50°C. Thus the test substance was considered hydrolytically unstable at pH 9. The preliminary tests at pH 4 and pH 7 indicated that an examination of the hydrolysis kinetics was essential.

Results of the Main Test

Table.2: Results of test 1 at pH 4 and test temperature 50°C

Duration (h)	C0in mg/L	Ctmg/L	Ct/ C0	log (Ct/ C0)	Decomposition in %
1.5	7501	5462	0.7282	-0.1378	27.2
19.0		5104	0.6805	-0.1672	32.0
23.5		4610	0.6145	-0.2115	38.6
39.5		3304	0.4405	-0.3560	56.0
47.5		2805	0.3739	-0.4272	62.6

 

Regression: -log (C_t/ C₀)= t' K_obs/2.303 with K_obs/2.303= b

b = 0.0090

Correlation: 0.9998

Calculations based on the analysis lead to:

K_obs= 0.0207 h^-1

t_1/2= 33.49 h

Table.3: Results of test 3 at pH 4 and test temperature 55°C

Duration (h)	C0in mg/L	Ctmg/L	Ct/ C0	log (Ct/ C0)	Decomposition in %
0	7215	7234	1.0026	0.0011	-0.3
15.5		4476	0.6204	-0.2073	38.0
21.4		3699	0.5127	-0.2902	48.7
24.0		3401	0.4714	-0.3266	52.9
40.0		2034	0.2819	-0.5499	71.8

 

Regression: -log (C_t/ C₀)= t' K_obs/2.303 with K_obs/2.303= b

b = 0.0137

Correlation: 0.9998

Calculations based on the analysis lead to:

K_obs= 0.0315 h^-1

t_1/2= 22.01 h

Table.4: Results of test 3 at pH 4 and test temperature 65°C

Duration (h)	C0in mg/L	Ctmg/L	Ct/ C0	log (Ct/ C0)	Decomposition in %
0	7204	7222	1.0025	0.0011	-0.3
7.3		4538	0.6299	-0.2007	37.0
23.0		1354	0.1879	-0.7260	81.2

 

Regression: -log (C_t/ C₀) = t' K_obs/2.303 with K_obs/2.303= b

b = 0.0313

Correlation: 0.9971

Calculations based on the analysis lead to:

K_obs= 0.072 h^-1

t_1/2= 9.63 h

Table.5: Results of test 1 at pH 7 and test temperature 50°C

Duration (h)	C0in mg/L	Ctmg/L	Ct/ C0	log (Ct/ C0)	Decomposition in %
3.0	7375	5823	0.7896	-0.1026	21.0
4.3		5284	0.7164	-0.1448	28.4
6.2		4711	0.6389	-0.1946	36.1
8.3		4094	0.5551	-0.2556	44.5

 

Regression: -log (C_t/ C₀) = t' K_obs/2.303 with K_obs/2.303= b

b = 0.0316

Correlation: 0.9823

Calculations based on the analysis lead to:

K_obs= 0.0728 h^-1

t_1/2= 9.52 h

Table.6: Results of test 3 at pH 7 and test temperature 35°C

Duration (h)	C0in mg/L	Ctmg/L	Ct/ C0	log (Ct/ C0)	Decomposition in %
0	5423	5404	0.9965	-0.0015	0.4
39.6		3602	0.6643	-0.1776	33.6
47.5		3361	0.6198	-0.2078	38.0
71.7		2734	0.5042	-0.2974	49.6

 

Regression: -log (C_t/ C₀)= t' K_obs/2.303with K_obs/2.303= b

b = 0.0043

Correlation: 0.9962

Calculations based on the analysis lead to:

K_obs= 0.0098 h^-1

t_1/2= 70.55 h

Table.7: Summary of the hydrolysis results and extrapolation at pH 4

Temperature in °C	t1/2	K	Experiment
50	33.49	0.0207	test 1 experiment 10
55	22.01	0.0315	test 3 experiment 14
65	9.63	0.0720	test 3 experiment 13
25	355.7	0.00195	extrapolation

 

Regression: In Kobs = - E/R *1/T+ const with E/R = band T in K

b = -9093

const = 24.26

correlation = 0.9999

t_1/2at 25°C=355.7 h =14.8 d

 

Table.8: Summary of the hydrolysis results and extrapolation at pH 7

Temperature in °C	t1/2	K	Experiment
50	9.52	0.0728	test 1 experiment 9
35	70.55	0.0098	test 3 experiment 11
25	300.0	0.00231	extrapolation

Regression: In Kobs = - E/R *1/T+ const with E/R = band T in K

b = -13297

const = 38.53

correlation = 1.000

t_1/2at 25°C=300.0 h =12.5 d

Validity criteria fulfilled:

yes

Conclusions:

Under the test conditions, the extrapolated half life for hydrolysis of the test substance were found to be 14.8 and 12.5 d at pH 4 and at pH 7, respectively. The substance is hydrolytically unstable at pH 9 and 25°C based on the preliminary test results (DT50 < 12 h).

Executive summary:

A study was conducted to determine hydrolysis as a function of pH for the test substance according to OECD Guideline 111 and EU Method C.7, in compliance with GLP.

The flask containing the hydrolysis mixture was placed in a thermostatically controlled water bath at the selected temperature for the specified time. The pH was controlled and the concentration of the unhydrolysed test substance (main compound) was measured by HPLC. The preliminary tests were done at 50±0.5°C with buffers at pH 4, 7 and 9. At pH 9, more than 50% of the reaction was observed after 2.4 h at 50°C (t_1/2< 1 d). Thus the test substance was considered hydrolytically unstable at the pH 9 and testing at pH 4 and pH 7 was considered essential.

Main tests included Test 1 at 50±0.5°C with pH 4 and pH 7, Test 3 at 55 and 65±0.5°C with pH 4 and at 35±0.5°C with pH 7. At pH 4 the half-life period was determined by extrapolation of the results of the experiments at 50, 55 and 65°C to a temperature of 25°C. It was found to be 14.8 d. At pH 7 the extrapolated half-life period at the temperature of 25°C, was found to be 12.5 d.

Under the test conditions, the extrapolated half life for hydrolysis of the test substance was found to be 14.8 and 12.5 d at pH 4 and at pH 7, respectively.

Description of key information

Under the test conditions, the extrapolated half life for hydrolysis of the test substance were found to be 14.8 and 12.5 d at pH 4 and at pH 7, respectively. The substance is hydrolytically unstable at pH 9 and 25°C based on the preliminary test results (DT50 < 12 h).

Key value for chemical safety assessment

Half-life for hydrolysis:

12.5 d

at the temperature of:

25 °C

Additional information

A study was conducted to determine hydrolysis as a function of pH for the test substance according to OECD Guideline 111 and EU Method C.7, in compliance with GLP. The flask containing the hydrolysis mixture was placed in a thermostatically controlled water bath at the selected temperature for the specified time. The pH was controlled and the concentration of the unhydrolysed test substance (main compound) was measured by HPLC. The preliminary tests were done at 50±0.5°C with buffers at pH 4, 7 and 9. At pH 9, more than 50% of the reaction was observed after 2.4 h at 50°C (t_1/2< 1 d). Thus the test substance was considered hydrolytically unstable at the pH 9 and testing at pH 4 and pH 7 was considered essential. Main tests included Test 1 at 50±0.5°C with pH 4 and pH 7, Test 3 at 55 and 65±0.5°C with pH 4 and at 35±0.5°C with pH 7. At pH 4 the half-life period was determined by extrapolation of the results of the experiments at 50, 55 and 65°C to a temperature of 25°C. It was found to be 14.8 d. At pH 7 the extrapolated half-life period at the temperature of 25°C, was found to be 12.5 d. Under the test conditions, the extrapolated half life for hydrolysis of the test substance was found to be 14.8 and 12.5 d at pH 4 and at pH 7, respectively (Schminke, 2004a).