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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:
23 June 2016
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
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))
Version / remarks:
2008
Deviations:
no
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))
Version / remarks:
2001
Deviations:
no
GLP compliance:
yes
Type of method:
HPLC estimation method
Media:
soil
Radiolabelling:
no
Details on study design: HPLC method:
CALCULATION OF PKA
-Perrin calculation method (pKalc 5.0, module in Pallas 3.0, CompuDrug International, USA) for the logarithm range of 1 - 14.
-Result: pKa acidic: none; pKa basic: none.

HPLC CONDITIONS
- Based on the calculated pKa values, the mobile phase was not buffered.
- Instrument: Acquity UPLC system (Waters, USA)
- Detector: Acquity UPLC TUV detector (Waters, USA)
- Column: Acquity UPLC HSS Cyano, 100 mm x 2.1 mm i.d., dp = 1.8 μm (Waters, USA)
- Column temperature: 35°C ± 1°C
- Mobile phase: 55/45 (v/v) methanol/water
- Flow: 0.4 mL/min
- Injection volume: 5 μL
- UV detection: 210 nm

UNRETAINED SUBSTANCE, REFERENCE SUBSTANCES AND TEST SUBSTANCE SOLUTIONS
- Unretained substance: formamide.
- Reference substances with known log Koc values in the range 1.26 - 5.63: see the table in Results and Discussion.
- Solutions of the unretained substance and of the mixture of reference substances were prepared in mobile phase.
- A 1000 mg/L stock solution of the test item was prepared in methanol. The stock solution was diluted to obtain an end solution of 55/45 (v/v) methanol/water. The final concentration of the test item solution was 10.0 mg/L.

INJECTIONS
- Solutions of the unretained substance, the reference substances and the test substance were injected in duplicate.
- Blank solutions (55/45 (v/v) methanol/water) were analysed by single injection.

DATA HANDLING
- Dead time (t0)= mean retention time of the unretained substance
- Duplicate capacity factors (k') for each reference substance were calculated from the retention times (tr): k'= (tr-t0)/t0
- Log k’ values of the references substances were plotted against the known log Koc values.
- Linear regression analysis (least squares method) resulted in the following regression line: log k’ = 0.322 x log Koc– 0.804 (r=0.98, n=16)
- Capacity factor (k') of the test substance was calculated from its retention time and the dead time.
- Log Koc of the substance was calculated by substituting its mean log k’ in the regression line.
Key result
Type:
log Koc
Value:
3.28 dimensionless
Temp.:
20 °C
Remarks on result:
other: Koc= 1.9E03 L/kg
Details on results (HPLC method):
The chromatogram of the test substance solution showed one peak with a retention time of 2.2 minutes.

Table: Results Adsorption coefficient (HPLC estimation method):

Substance

tr,1 (min)

tr, 2 (min)

Mean tr (min)

Log Koc

Koc

Formamide (t0)

0.792

0.792

0.792

 

 

Acetanilide

1.060

1.057

 

1.26

 

Monuron

1.321

1.321

 

1.99

 

2,5-Dichloroaniline

1.515

1.511

 

2.55

 

Naphthalene

1.773

1.768

 

2.75

 

Benzoic acid phenylester

2.080

2.077

 

2.87

 

Fenthion

2.844

2.828

 

3.31

 

Phenanthrene

3.120

3.124

 

4.09

 

4,4’-DDT

7.928

7.859

 

5.63

 

Test item

2.2

2.212

2.206

3.28

1.9 x 103

Note: log Koc values for the reference substances are mentioned in OECD TG 121 and are based on soil adsorption data.

Conclusions:
The log Koc for the substance was determined to be 3.28 (Koc= 1.9E03).

Executive summary:

The HPLC estimation method based on soil-adsorption reference data was used for the determination of the adsorption coefficient (Koc) of the substance. The mobile phase was 55/45 (v/v) methanol/water and the wavelength of detection 210 nm. Duplicate measurements were performed. The chromatogram of the test substance solution (10 mg/L) showed one peak with a retention time of 2.2 minutes. The log Koc for the substance was determined to be 3.28 (Koc= 1.9E03). The study was performed in accordance with EC C.9 and OECD 121 and in compliance with GLP.

Description of key information

The HPLC estimation method based on soil-adsorption reference data was used for the determination of the adsorption coefficient (Koc) of the substance. The mobile phase was 55/45 (v/v) methanol/water and the wavelength of detection 210 nm. Duplicate measurements were performed. The chromatogram of the test substance solution (10 mg/L) showed one peak with a retention time of 2.2 minutes. The log Koc for the substance was determined to be 3.28 (Koc= 1.9E03 L/kg).The study was performed in accordance with EC C.9 and OECD 121 and in compliance with GLP.

Key value for chemical safety assessment

Koc at 20 °C:
1 900

Additional information

The sorption coefficient of dibutyl itaconate was also studied in a GLP compliant adsorption batch equilibrium test (OECD 106) with three soils.

Before the kinetics experiment started, three preliminary tests were conducted in order to determine a suitable soil:solution ratio, the stability of the test item and the sorption to the container material. It was cocluded that the optimal soil:solution ratio for the kinetics experiment was 1:200. The test item was shown to be stable and did not adsorb significantly onto the test vessel wall.

In the 48h kinetics experiment no adsorption equilibrium could be reached and therefore it was decided not to perform the isotherm experiment.  Based on the results of this study, no adsorption constant could be derived for the test item. The Koc was subsequently determined by a HPLC method (OECD 121).

[LogKoc: 3.28]

[LogKoc: 3.28]