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Adsorption / desorption

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adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
key study
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: fullt compliant to guideline and GLP study
according to guideline
OECD Guideline 121 (Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC))
GLP compliance:
Type of method:
HPLC estimation method
other: HPLC
Test temperature:
Column temperature was room temperature, 22 ± 1 °C
Details on study design: HPLC method:
- Apparatus:
- Type: Pump Dionex P580 Pump, Injector Rheodyne 8125
- Type, material and dimension of analytical (guard) column: Reprosil-Pur CN Dr. Maisch, 4.6 mm i.D., 100 mm length, particle size 3 pm
- Detection system: Dionex, UVD 170S

- Type: A mixture of 55% methanol and 45% water, isocratic, was used.
- Experiments with additives carried out on separate columns: no
- pH: pH of the eluent was 6.92
- Solutes for dissolving test and reference substances: mobile phase

- Method: by inert substances which are not retained by the column: sodium nitrate

- Identity:
Name CAS-No.
Sodium nitrate 7631-99-4
Phenole 108-95-2
Methylbenzoate 93-58-3
3,5-Dinitrobenzamide 121-81-3
Naphthalene 91-20-3
1,2,3-Trichlorbenzene 87-61-6
Pyrazophos 13457-18-6
DDT 50-29-3

One vial was filled with the reference item mix and one vial with the test item solution. The vials were analysed using HPLC with the program described above. Three injections were measured from the reference item mix, three injections from the test item and again three injections from the reference item mix.
The data was saved, the retention times of the eight peaks of the reference item mix and the retention times of the two peaks of the test item were used for further calculations.

- Calculation of capacity factors k': The calibration function was drawn up from the six measurements of the capacity factors of the reference items. By plotting the (known) log Koc values of the reference items against the mean log capacity factors and performing linear regression, a calibration function was obtained.
- Determination of the log Koc value:
With the calculated capacity factors for the test item, each log Koc from the three determinations was calculated.
Finally, mean and standard deviation of the log Koc were calculated.
Key result
log Koc
Details on results (HPLC method):
- Retention times of reference substances used for calibration:
Compound MeRTan RTStand. Dev. RTRelativeStand. Dev. k'
min. min. %
Sodium nitrate 0.803 0.001 0.129 0
Phenole 1.951 0.005 0.255 1.4306
Methylbenzoate 2.140 0.004 0.186 1.6665
3,5-Dinitrobenzamide 2.463 0.009 0.380 2.0687
Naphthalene 3.215 0.009 0.270 3.0052
1,2,3-Trichlorbenzene 3.903 0.016 0.407 3.8621
Pyrazophos 5.411 0.031 0.572 5.7411
DDT 13.703 0.116 0.850 16.072
Validity criteria fulfilled:
Using the correlation log k' / log Koc, the log Kocs of the peaks of the test item Benzyltoluene were calculated. The validity criteria and results (mean ± standard deviation) are presented in the following table:
Table 9.3-a Validity Criteria and Results
Peak Parameter Criterion Found Assessment
1 Range (Max - Min. log Koc) < 0.25 0.009 valid
Value within Range of Calibration 1.32 - 5.63 3.561 ± 0.004 valid
2 Range (Max - Min. log KOC) < 0.25 0.009 valid
Value within Range of Calibration 1.32 - 5.63 3.689 ± 0.005 valid

Variations in the retention times of reference items and test item are very small. Therefore a stable configuration of the HPLC-column can be assumed.
The correlation log k'/log Koc is very accurate, as calibration gave a coefficient of determination r2 = 0.9911.
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. Seven reference items with different retention times were used to pro-duce 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 Benzyltoluene on the column.

First, a solution of the reference items was analysed three times with HPLC, then a solution of the test item (three times) and finally three more times the solution with the references.

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= 0.9911 and r = 0.9955.

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


Mean retention time [min]

Log Koc±sd



3.561 ± 0.004



3.689 ± 0.005

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

Description of key information

log Koc has been estimated by HPLC to be (2 isomers): 3.6 and 3.7. The mean is used as key parameter

Key value for chemical safety assessment

Koc at 20 °C:
5 012

Additional information