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Adsorption / desorption

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adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
according to
OECD Guideline 121 (Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC))
Version / remarks:
GLP compliance:
yes (incl. certificate)
Type of method:
HPLC estimation method
Details on study design: HPLC method:
- Apparatus: HPLC
- Type:
- Type, material and dimension of analytical (guard) column: Reprosil PurCN 125*4.6 mm, with pre-column Phenomenex Securi-tyGuard CN, 4x3 mm
- Detection system: Dionex, DAD-3000

- Type: isocratic methanol/water 55/45 (% v/v), degassed
- Experiments with additives carried out on separate columns: yes / no
- pH: 7
- Solutes for dissolving test and reference substances: -

- Method: by inert substances which are not retained by the column (Sodium nitrate)

- Identity: Phenol, Methylbenzoate, Naphthalene, 1,2,3-Trichlorobenzene, Phenanthrene, 4,4'-DDT

- Quantity of test substance introduced in the column: 10 µg
- Quantity of reference substances: 10 µg
- Intervals of calibration:

- Number of determinations: 3 (test item)/ 6 (reference substances)

- Calculation of capacity factors k': log k’ = 0.1938 * logKOC – 0.0129
- Calculation of retention times:
- Determination of the log Koc value: log KOC = (log k’ + 0.0129) / 0.1938
Key result
log Koc
25 °C
Details on results (HPLC method):
- Retention times of reference substances used for calibration:
- Details of fitted regression line (log k' vs. log Koc): log k’ = 0.1938 * logKOC – 0.0129

- Average retention data for test substance: 4.659 min
Validity criteria fulfilled:
Variations in the retention times of reference items and test item are very small. Therefore, a stable con-figuration of the HPLC-column can be assumed.
The correlation log k’/log KOC is sufficiently accurate. As calibration gave a coefficient of determination r2 = 0.999.
As peak 2 showed a relative area < 5 %, it was considered as minor peak and only Peak 1 was used for evaluation of the log KOC of the test item.
No observations were made, which might give doubts concerning the validity of the study outcome.
Executive summary:

The study was performed using a HPLC with a cyanopropyl chemical bound resin on a silica base column. Six reference items with different retention times were used to produce a calibration curve, since retention time on cyanopropyl columns and KOC are correlated. The reference items were chosen on behalf of the retention time of the test item 2,2'-Azobis(2,4-dimethylvaleronitrile) on the column/ on the results of the pre-test.


A solvent blank followed by three injections of a solution of the reference items were analysed with HPLC, then three injections of a solution of the test item; and finally three injections of the solution with the reference items, in total ten runs.

For each reference item, the capacity factor k’ was calculated from the retention time of sodium nitrate and the retention time of the respective reference item. A calibration function was set up using the literature values for KOC of the reference items and the mean capacity factor of the six determinations. In the graph log k’ versus log KOC, linear regression was performed, giving r2 = 0.999.


The chromatogram of the test item gave two peaks. With the help of the calibration function log K versus log KOC, the corresponding log KOC values were determined as:

 Peak Mean retention time [min] Log KOC + sd

1* 4.659 3.108 + 0.003

2 5.012 3.312 + 0.004

* (major peak, used for evaluation)

These values are the mean ± standard deviation of three independent determinations


Description of key information

The key value is determined in a HPLC screening study. The value indicates a low mobility of the test substance in soil.

Key value for chemical safety assessment

Koc at 20 °C:
1 282

Additional information