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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:
15.12.15
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
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 (incl. certificate)
Type of method:
HPLC estimation method
Media:
soil/sewage sludge
Radiolabelling:
no
Test temperature:
25±1 °C
Details on study design: HPLC method:
EQUIPMENT
- Apparatus: DIONEX Ultimate3000
- Type:
- Type, material and dimension of analytical (guard) column: Reprosil Pur CN (Dr. Maisch) 125*4.6 mm, 3 µm; Phenomenex SecurityGuard CN, 4*3 mm
- Detection system: UV detector VWD-3400RS (210 nm)

MOBILE PHASES
- Type: isocratic methanol/water 55/45 (% v/v), degassed
- Experiments with additives carried out on separate columns: no
- pH: 6.38
- Solutes for dissolving test and reference substances:

DETERMINATION OF DEAD TIME
- Method: The dead time t0 was measured by using an unretained compound (sodium nitrate) which was included in the mix of the reference items.

REFERENCE SUBSTANCES
- Identity: Sodium nitrate, Phenol, methylbenzoate, Naphthalene, 1,2.3-trichorobenzene, Phenanthrene, DDT

DETERMINATION OF RETENTION TIMES
- Quantity of test substance introduced in the column:
- Quantity of reference substances: Sodium nitrate (2.0 mg/L), Phenol (4.0 mg/L), methylbenzoate (2.0 µL/L), Naphthalene ( 2.0 mg/L), 1,2.3-trichorobenzene (4.0 mg/L), Phenanthrene (3.0 mg/L), DDT (10 mg/L)
- Intervals of calibration:

REPETITIONS
- Number of determinations: triplicate

EVALUATION
- Calculation of capacity factors k':
- Calculation of retention times:
- Determination of the log Koc value:
Key result
Type:
log Koc
Value:
2.008 dimensionless
pH:
6.38
Temp.:
25 °C
Details on results (HPLC method):
- Retention times of reference substances used for calibration: Sodium nitrate (1.065 min), Phenol (2.825 min), methylbenzoate (3.292 min), Naphthalene (4.592 min), 1,2.3-trichorobenzene (5.242 min), Phenanthrene (7.445 min), DDT (15.588 min)
- Details of fitted regression line (log k' vs. log Koc): R2=0.9987
- Graph of regression line attached
- Average retention data for test substance: 3.500 min
Validity criteria fulfilled:
yes
Conclusions:
Variations in the retention times of the 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 sufficiently accurate, as calibration gave a coefficient of determination r2=0.9987.
As peaks 1, 2, 3, 4 and 5 showed a relative area < 5 %, they were considered as minor peaks. Although area is not necessarily correlated to absolute concentration if a UV detector is used, it is assumed that the test item consists mainly of the peak 6. Using the given correlation the log Koc of the test item was calculated as 2.008 ± 0.000 (mean ± standard variation).
Executive summary:

The study was performed using a HPLC with a cyanopropyl chemical bound resin on a silica basecolumn. Six reference items with different retention times were used to produce a calibration curve, since retention time on cyano-propyl columns and KOCare correlated. The reference items were chosen on behalf of the retention time of the test item2,2'-Azobis (4-methoxy-2,4-dimethyl valeronitrile)on the column.

 

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, totalling to 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 KOCof 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= 0.9987 and r = 0.9994.

 

The chromatogram of the test item gave six peaks.As peaks 1, 2, 3, 4 and 5 showed a relative area < 5 %, they were considered as minor peaks.

Although area is not necessarily correlated to absolute concentration if a UV detector is used, it is assumed that the test item consists mainly of the peak 6.

Using the correlation log k’ / log KOC, the log KOCof the test item2,2'-Azobis (4-methoxy-2,4-dimethyl valeronitrile)was calculated as 2.008 ± 0.000 (mean ± standard deviation).

Peak

Mean Area
[mAU*min]
[1]

Rel. Area %

Mean Retention Time [min]

log KOC
±Stand. Dev

1

0.0782

0.49

1.094

-7.234 ± 0.804

2

0.4332

2.69

2.125

0.291 ± 0.000

3

0.1469

0.91

2.592

1.045 ± 0.000

4

0.5741

3.57

2.767

1.269 ± 0.000

5

0.1901

1.18

2.992

1.525 ± 0.000

6

14.6595

91.15

3.500

2.008 ± 0.000

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

 

Description of key information

The soil partition coefficient is determined in an OECD 121 screening study.

Key value for chemical safety assessment

Koc at 20 °C:
2

Additional information