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Adsorption / desorption

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Reference
Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
key study
Study period:
October 2005
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Study conducted in compliance with agreed protocols, with no or minor deviation from standard test guidelines and/or minor methodological deficiencies, which do not affect the quality of relevant results.
Reason / purpose:
reference to other study
Reference:
Composition 0
Qualifier:
according to
Guideline:
OECD Guideline 121 (Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC))
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.19 (Estimation of the Adsorption Coefficient (KOC) on Soil and Sewage Sludge Using High Performance Liquid Chromatography (HPLC))
Deviations:
no
GLP compliance:
yes (incl. certificate)
Type of method:
HPLC estimation method
Test material information:
Composition 1
Radiolabelling:
no
Test temperature:
35°C (column temperature)
Details on study design: HPLC method:
TEST SYSTEM
DETERMINATION OF Koc:
Main test:
A High Performance Liquid Chromatograph with a spectrophotometric detector was used. The stationary phase was a cyanopropyl chemically bound resin on silica basis (Hypersil BDS-CN). The mobile phase was 55/45 (v/v) methanol/water. A temperature controlled column
compartment at 35°C was used. See Analytical conditions below:

Additional test:
In order to show that the test substance can be passed through the HPLC coluumn and can be detected using a spectophotometric detector, a second mobile phase (100% methanol) was used.

PERFORMANCE OF THE TEST:
Analytical conditions:
Column:-
Stationary phase: Hypersil BDS-CN
Dimensions: 150 mm x 4.6 i.d. mm; dp = 5 µm
Brand: Alltech
Column temperature: 35°C
Mobile phase (main test): 55/45 (v/v) methanol/Milli-Q water
Mobile phas (additional test): 100% methanol
Flow: 1 ml/min
Injection volume: 10 µl
Detection: Spectrophotometric (wavelength of 210 nm)

Preparation of the solutions:
As a reference solution, 2,4-DDT in methanol was used. This solution was diluted by a factor of100 with mobile phase.
The test substance did not dissolve in mobile phase. Therefore, a 0.408 g/l stock solution of EA-3098 was prepared in methanol. In order to dissolve the test substance, the solution was sonicated for 20 minutes. Methanol was used as the test substance blank solution.

Injections:
The solutions were injected in the following sequence: mobile phase, 2,4-DDT solution, test substance solution (in duplicate) and methanol. The chromatograms of the test substance solution and methanol were recorded for 30 minutes. The chromatograms of the 2,4-DDT solution and mobile phase were recorded for 10 minutes.


INTERPRETATION:
- Calculation of capacity factors k':
The capacity factor (k') is calculated from the retention of the substance concerned (tr) and unretarded component (to):

k' = (tr - to)/ to

Using the capacity factors of the reference substances, a plot of log Koc versus log k' was constructed, using linear regression analysis. The log Koc value of each component of the test substance was calculated from the following equation:

Log K' = a * Log Koc + b
Computational methods:
Calculation of pKa:
The pKa values for EA-3098 were calculated using computer software: pKacl version 5.0.

Refer to 'dissociation constant' for full details.
Type:
log Koc
Value:
> 5.63
Temp.:
35 °C
Type:
Koc
Value:
> 430 000
Temp.:
35 °C
Details on results (HPLC method):
- Retention times of reference substances used for calibration: 6.7 minutes

- Average retention data for test substance: Cannot be observed within a run time of 30 minutes
Transformation products:
no

Calculation of pKa values

Using a computer program, pKa values were calculated for EA-3098 to be:

-0.48 and 0.12 basic group (RCONHR)

16.28 and 16.88 acidic group (RRCHOH)

Because the test substance is not ionised for more than 10% within pH 5.5 to 7.5, the mobile phase used during the HPLC methid was not buffered.

Main test

In the chromatograms of the 0.408 g/l stock solution of EA-3098 which were recorded for 30 minutes, no test substance peak was observed. Under the same chromatographic conditions, the retention time of 2,4 -DDT (log Koc = 5.63) was 6.7 minutes. It was assumed that EA-3098 elutes after the reference substance 2,4 -DDT and cannot be observed within a run time of 30 minutes.

Additional test

In order to show that the test substance can be passed through the HPLC column and can be detected using a spectrophotometric detector, a second mobile phase (100% methanl) was used. One large test substance peak at a retention time of 1.9 minutes was observed in the chromatograms of the 0.408 g/l EA-3098 test solution.

Based on this, it was conluded that EA-3098 elutes after the reference substance with known log Koc of 5.63. Hence, the log Koc of EA-3098 is >5.63 (Koc >4.3 x 105).

Please see attached Appendix for chromatograms.

Validity criteria fulfilled:
yes
Conclusions:
The adsorption coefficient (koc) of EA-3098 was determined to be >4.3E+05 (log koc >5.63) at 35°C.
Executive summary:

The estimation of the adsorption coefficient (Koc) in soil and on sewage sludge using HPLC was based on the following guidelines:

* OECD 121 "Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using HPLC"

* EEC Directive 2001/59/EC Method C.19 "Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using HPLC"

According to these guidelines, the estimation of the adsorption coefficient (Koc) for test substances that are ionised for at least 10% within pH 5.5 to 7.5, should be performed with both the ionised and non-ionised form. Based on calculated pKa values (16.28 and 16.88 for an acidic group and -0.48 and 0.12 for a basic group), it was decided to perform the HPLC method at neutral pH.

The adsorption coefficient (koc) of EA-3098 was determined to be >4.3 x 105 (log koc >5.63) at 35°C.

Description of key information

The adsorption coefficient (koc) of EA-3098 was determined to be >4.3 x 10E5 (log koc >5.63) at 35°C.

Key value for chemical safety assessment

Koc at 20 °C:
430 000

Additional information

The estimation of the adsorption coefficient (Koc) in soil and on sewage sludge using HPLC was based on the following guidelines:

* OECD 121 "Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using HPLC"

* EEC Directive 2001/59/EC Method C.19 "Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using HPLC"

According to these guidelines, the estimation of the adsorption coefficient (Koc) for test substances that are ionised for at least 10% within pH 5.5 to 7.5, should be performed with both the ionised and non-ionised form. Based on calculated pKa values (16.28 and 16.88 for an acidic group and -0.48 and 0.12 for a basic group), it was decided to perform the HPLC method at neutral pH.

The adsorption coefficient (koc) of EA-3098 was determined to be >4.3 x 105(log koc >5.63) at 35°C.

[LogKoc: 5.63]