Chromate(5-), bis[4-(hydroxy-κO)-7-[2-(2-hydroxy-1-naphthalenyl)diazenyl]-3-[2-[2-(hydroxy-κO)- 3-nitro-5-sulfophenyl]diazenyl]-2-naphthalenesulfonato(4-)]-, sodium (1:5)

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

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)

GLP compliance:

yes

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

The concentration of the substance was determined using HPLC method. The conditions were:
-Sample pre-treatment preliminary test
Immediately after samples were taken, they were cooled down to room temperature. Then, each pH 4 and pH 7 sample was diluted, in duplicate, 40 times with Milli-Q water, prior to analysis. Each pH 9 sample was diluted 66.67 times with Milli-Q water, prior to analysis.
-Sample pre-treatment test 1
Immediately after samples were taken, they were cooled down to room temperature. Then, each sample was diluted, in duplicate, 80 or 100 times with Milli-Q water, prior to analysis.
-Blank solutions
At the first day of each test, blank buffer solutions were pre-treated in a similar fashion to the corresponding test solutions.

Buffers:

A sterile 0.05 M acetate buffer pH 4; sodium acetate (p.a., Merck, Darmstadt, FRG)/acetic acid (p.a., Merck) in Milli-Q water (Millipore Corp., Bedford, MA., USA);
A sterile 0.05 M phosphate buffer pH 7; Potassium dihydrogenphosphate (p.a., Merck)/sodium hydroxide (p.a., Merck) in Milli-Q water;
A sterile 0.05 M borate buffer pH 9; bore acid (p.a., Merck)/potassium chloride (p.a,, Merck)/sodium hydroxide in Milli-Q water.

Details on test conditions:

-Preparation of the test Solutions
Prior to the performance of each test, the test solutions were freshly prepared. Therefore, an accurately weighed amount of between 46 - 80 mg test substance was added to 50.0 ml buffer solution pH 4, pH 7 or pH 9. The resultant solutions were filter-sterilized through a 0.2 µm membrane filter  (FP 030/3, Schleicher & Schuell, 's-Hertogenbosch, The Netherlands) and transferred into sterile glass vessels.
To exelude oxygen, nitrogen gas was bubbled through each solution for 5 minutes. Thereafter, each vessel was tightly sealed with a septum-crimpcap.

-Preliminary test
After preparation, the test solutions at pH 4, 7 and 9 were placed in a thermostatically controlled waterbath at 50.0 ± 0.5°C in the dark. The concentration of the test substance was determined immediately after preparation  (T=:0), after 2.4 hours and after 5 days.

-Test 1
During the preliminary test, significant hydrolysis was observed at pH 4 and 9. Therefore, test 1 was carried out at these pH values.
After preparation, the test solutions pH 4 and 9 were placed in a thermostatically controlled waterbath at 60.0 ±  0.5°C  in the dark. The concentration of the test substance at pH 4 was determined immediately after preparation (T=0) and 120.5, 144.5, 168, 214.6, and 287.4 hours after T=0.
The concentration of the test substance at pH 9 was determined immediately after preparation (T=0) and 120.1, 144.1, 168, 214.2, and 287 hours after T=0.

-pH measurements
For each test solution, the pH value at room temperature was determined at the beginning and at the end of the test (preliminary test) or at the beginning of the test.

Duration:

5 d

pH:

4

Temp.:

50 °C

Initial conc. measured:

716 mg/L

Remarks:

preliminary test

Duration:

5 d

pH:

7

Temp.:

50 °C

Initial conc. measured:

972 mg/L

Remarks:

preliminary test

Duration:

5 d

pH:

9

Temp.:

50 °C

Initial conc. measured:

1 569 mg/L

Remarks:

preliminary test

Duration:

12 d

pH:

4

Temp.:

60 °C

Initial conc. measured:

848 mg/L

Remarks:

test 1

Duration:

12 d

pH:

9

Temp.:

60 °C

Initial conc. measured:

1 317 mg/L

Remarks:

test 1

Number of replicates:

The test concentration was measured in duplicate

Preliminary study:

At pH 7, a decrease in concentration < 10% was observed after 5 days (half-life time > 1 year).
At pH 4 and 9, a decrease in concentration < 50% after 2.4 hours and a decrease 1n concentration > 10%  after 5 days was observed. Therefore, no further testing was necessary at pH 7. Test 1 had to be performed at pH 4 and 9.

Transformation products:

no

% Recovery:

93

pH:

7

Temp.:

50 °C

Duration:

ca. 5 d

Remarks on result:

other: preliminary test

% Recovery:

82

pH:

4

Temp.:

60 °C

Duration:

ca. 12 d

Remarks on result:

other: test 1

% Recovery:

88

pH:

9

Temp.:

60 °C

Duration:

ca. 12 d

Remarks on result:

other: test 1

Key result

Remarks on result:

hydrolytically stable based on preliminary test

According to the guideline, at least 4 samples covering the range 20 to 70 % of hydrolysis should be analysed during test 1 in order to test for pseudo-first order behaviour. However in this case even after 287 hours the amount of hydrolysis was still below 20% at both pH 4 and 9. After an initial drop in the test substance concentration the concentration started to fluctuate. For this reason, it is not probable that a larger decrease will be found if test 1 is continued for a longer time period.

Therefore, no more samples were taken.

Validity criteria fulfilled:

yes

Conclusions:

The substance is hydrolytically stable at pH 7, and hydrolytically unstable at pH 4 and 9, under the conditions of the test.

Executive summary:

The purpose of the study was to examine the hydrolysis behaviour of the test substance at pH values normally found in the environment (pH 4-9), according to the method C.7 of EEC-Directive 92/69 EEC. During the preliminary test, significant hydrolysis was observed at pH 4 and 9. Therefore, test was carried out at these pH values. After 287 hours the amount of hydrolysis was still below 20 % at both pH 4 and 9. As after an initial drop in the test substance the concentration started to fluctuate, it was not probable that a larger decrease will be found if test was continued for a longer time period. Therefore, no more samples were taken.

The substance was found to be hydrolytically stable at pH 7, and hydrolytically unstable at pH 4 and 9, under the conditions of the test.

Description of key information

hydrolytically stable at pH 7 and hydrolytically unstable at pH 4 and 9

Additional information

The purpose of the study was to examine the hydrolysis behaviour of the test substance at pH values normally found in the environment (pH 4-9), according to the method Directive 92/69 EEC, Annex V. Part C, 7.

The substance was found to be hydrolytically stable at pH 7, and hydrolytically unstable at pH 4 and 9, under the conditions of the test.