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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
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 121 (Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC))
Deviations:
no
Remarks:
The study was conducted according to the test guidelines in effect at the time of study conduct.
Qualifier:
according to guideline
Guideline:
EU Method C.19 (Estimation of the Adsorption Coefficient (KOC) on Soil and Sewage Sludge Using High Performance Liquid Chromatography (HPLC))
Deviations:
no
Remarks:
The study was conducted according to the test guidelines in effect at the time of study conduct.
GLP compliance:
yes
Type of method:
HPLC estimation method
Media:
soil
Radiolabelling:
no
Test temperature:
25°C
Details on study design: HPLC method:
EQUIPMENT
- Apparatus: HPLC
- Type: Agilent 1200 Series Liquid Chromatograph with Chemstation software
- Type, material and dimension of analytical (guard) column: HyperClone CN (CPS) (25 cm x 4.6 mm internal diameter); 25°C
- Detection system: UV set at 210 nm

MOBILE PHASES
- Type: Acetonitrile:buffer solution (55:45 v/v); a phosphate buffer was used at pH 4 and a borate buffer at pH 9; 1.0 mL/minute flow rate
- Experiments with additives carried out on separate columns: no
- pH: 4 and 9

DETERMINATION OF DEAD TIME: An internal standard (formamide; 200 mg/L) with no retention in the HPLC column was used to determine the deadtime of the HPLC system).

REFERENCE SUBSTANCES
Acetanilide: 10 mg/L
Nitrobenzene: 10 mg/L
Naphthalene: 3 mg/L
2-Methylnaphthalene: 3 mg/L
Anthracene: 10 mg/L
DDT: 10 mg/L

DETERMINATION OF RETENTION TIMES: The sorption behaviour of the test substance on soil can be investigated using high performance liquid chromatography (HPLC). This is performed on commercially available analytical columns packed with a solid phase containing a moderately polar stationary phase with lipophilic and polar moieties (e.g. cyano-propyl bonded phase). The chemicals injected onto the column move along it by partitioning between the mobile phase and the stationary phase. The velocity of each component thereby depends on the degree of adsorption on the stationary phase. The dual nature of the stationary phase allows for interaction of polar and apolar parts of a molecule in a similar way as is the case for soil. This enables the relationship between the retention time on such a column and the adsorption coefficient on the organic parts of the soil to be established.

REPETITIONS
- Number of determinations: 2
Analytical monitoring:
no
Computational methods:
The adsorption coefficient is deduced from the capacity factor, k, given by
k = (tr – t0)/t0
where tr is the measured retention time of sample or reference
and t0 is the retention time of the internal deadtime standard.
A calibration plot of log10k versus log10Koc is constructed for the reference standards. The logarithm of the capacity factor for the test substance was then calculated and the log10Koc value was determined by interpolation.
Key result
Type:
log Koc
Value:
1.7
Temp.:
25 °C
Remarks on result:
other: pH 4
Key result
Type:
log Koc
Value:
1.3
Temp.:
25 °C
Remarks on result:
other: pH 9
Key result
Type:
Koc
Value:
49
Temp.:
25 °C
Remarks on result:
other: pH 4
Key result
Type:
Koc
Value:
18
Temp.:
25 °C
Remarks on result:
other: pH 9
Details on results (HPLC method):
- Retention times of reference substances used for calibration:
Acetanilide: 3.449 and 3.453 min at pH 4; 3.350 and 3.344 min at pH 9
Nitrobenzene 4.229 and 4.235 min at pH 4; 3.972 and 3.959 min at pH 9
Naphthalene: 4.976 and 4.984 min at pH 4; 4.598 and 4.578 min at pH 9
2-Methylnaphthalene: 5.331 and 5.341 min at pH 4; 4.889 and 4.865 min at pH 9
Anthracene: 5.975and 5.986 min at pH 4; 5.450 and 5.421 min at pH 9
DDT: 9.080 and 9.106 min at pH 4; 7.982 and 7.925 min at pH 9

- Average retention data for test substance: 3.731 minutes at pH 4 and 3.424 at pH 9
Validity criteria fulfilled:
yes
Conclusions:
The Koc value for the test item at pH 4 was 49 (log Koc = 1.7) .
The Koc value for the test item at pH 9 was 18 (log Koc = 1.3).

This study and the conclusions which are drawn from it fulfil the quality criteria (validity, reliability, repeatability).
Executive summary:

A study was performed to determine the adsorption coefficient of the test substance. The study was designed in accordance with accepted principles in order to meet the requirements of REACH Regulation (EU) No 1907/2006 of the European Parliament and of the Council. The method followed is amongst those described in Commission Regulation (EC) No. 440/2008 (Method C.19) and the OECD Guidelines for the Testing of Chemicals (Method 121). As the test substance contains ionisable functional groups, separate tests were performed at pH 4 and pH 9, at the extremes of the pH range of environmental relevance.

The test substance was determined to have log10Koc values of 1.7 and 1.3, equivalent to Koc values of 49 and 18, at pH 4 and pH 9 respectively.

Description of key information

Log Koc: 1.7 at 25°C and pH 4
Log Koc: 1.3 at 25°C and pH 9
Koc: 49 at 25°C and pH 4
Koc: 18 25°C and pH 9

Key value for chemical safety assessment

Additional information

Value used for CSA:

Koc at 25°C: 49

Log Koc at 25°C: 1.7

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