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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:
Between 26 May 2011 and 16 June 2011.
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
Study conducted in compliance with agreed protocols, with no or minor deviations from standard test guidelines and/or minor methodological deficiencies, which do not affect the quality of the relevant results. The study report was conclusive, done to a valid guideline and the study was conducted under GLP conditions.
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))
Deviations:
no
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))
Deviations:
no
GLP compliance:
yes (incl. certificate)
Remarks:
Date of Inspection: 26 and 27 October 2010 Date of Signature: 8 February 2011
Type of method:
HPLC estimation method
Media:
soil/sewage sludge
Radiolabelling:
no
Test temperature:
35 ºC
Details on study design: HPLC method:
Preparation of sample solution:
A solution of the test substance was prepared (12.5 mg in 50 ml methanol/water 55/45 v/v).

After equilibrium of the HPLC system, the calibration mixture was injected first, followed by the test chemical solution twice and the calibration mixture again.

Retention times tR were measured and averaged and the decimal logarithms of the capacity factors k were calculated. The linear regression parameters of the relationship:

log Koc = f (log k)

were also calculated from the data obtained with the calibration mixture and, therewith, log Koc of the test substance was determined from its measured capacity factor.

Finally solutions of the reference substances were injected individually to confirm the peak assignment.

Principle of the Method
Reverse phase High Performance Liquid Chromatography on cyanopropyl-modified silica stationary phase, containing lipophilic and polar moieties, is used.

While passing through the column among with the mobile phase the test substance interacts with the stationary phase. As a result of the partitioning between the mobile and stationary phase the test substance is retarded. The dual-composition of the stationary phase having polar and non-polar sites allows for interaction of polar and non-polar groups of a molecule in a similar way as it is the case for organic matter in soil or sewage sludge matrices. This enables the relationship between the retention time on the column and the adsorption coefficient on organic matter to be established.

Equipment and Conditions:
The sample, formamide and reference standard solutions were injected in duplicate using the following HPLC parameters:

HPLC System: Perkin Elmer (series 200) HPLC system comprising:
-a high pressure pump (module N2910102, serial number: 291N8051901A)
-an auto-sampler (module N2930100, serial number: 293N8052404A)
-a column compartment (module N2601581, serial number OVH0802151130)
-a reflective index detector (series 200a, serial number 125829)

-Column: 250 mm x 4.6 mm, Nucleodur 100-5 CN-RP (Macherey-Nagel)
Serial number: N10080027, batch 34518023
-Column temperature: 35 ºC
-Mobile phase: methanol/water 55/45 (v/v)
-Flow-rate: 1.0 ml/min
UV detector wavelength: dead time and reference standards: 210 nm, sample: 510 nm
-Injection volume: 100 µl












Analytical monitoring:
no
Key result
Type:
Koc
Value:
5 623 L/kg
Type:
log Koc
Value:
3.75
Details on results (HPLC method):
- Retention times of reference substances used for calibration: yes

- Details of fitted regression line (log k' vs. log Koc): yes

- Graph of regression line attached: yes

- Average retention data for test substance:

Transformation products:
not measured
Details on results (Batch equilibrium method):
Not applicable.
Statistics:
None stated.

Appendix 1: Adsorption coefficient calculations

Koc Partition Coefficient Determination by Reverse-Phase HPLC

REFERENCE SUBSTANCES

log Koc

tR1

 tR2  tRm  k  log k

Formamide

4.29

 4.52  4.40    

2 -Nitrobenzenamide

1.45

4.86

5.01  4.93  0.120  -0.921

Methyl Benzoate

1.80

6.44

 6.64  6.54  0.485  -0.314

Naphthalene

2.75

9.32

 9.60  9.46  1.148  0.060

1,2,3 -Trichlorobenzene

3.16

10.39

10.69  10.54  1.393  0.144

Phenanthrene

4.09

14.53

 14.91  14.72  2.342  0.370

4,4'-DDT

5.63

30.60

 31.51  31.05  6.051  0.782

tR1, tR2, tRm: retention times (1rst measurement, 2nd measurement, average)

k = (tR/t0)-1: capacity factor, t0: "dead time", i.e. retention time of formamide

Linear regression parameters: log Koc = a * log k + b

Correction coefficient r = 0.9410 a = 2.4777 c = 3.0973

TEST SUBSTANCE:Benzyl Salicylate

tR1

tR2

 tRm  k  log k  log koc

Benzyl Salicylate

12.46

12.55

 12.51  1.8396  0.2647  3.750
Validity criteria fulfilled:
yes
Conclusions:
The chromatograms of Benzyl Salicylate show one peak at an average retention time of 12.52 minutes, corresponding to an adsorption coefficient (log value) of 3.75.

Therefore: Adsorption coefficient (Koc) of Benzyl Salicylate: log Koc = 3.75
Executive summary:

Method

The determination was carried out using the HPLC screening method, Method C19 of Commission Directive 2001/59/EC (which constitutes Annex V of Council Directive 67/548/EEC), Method 121 of the OECD Guidelines for Testing of Chemicals, 22 January 2001.

Discussion

Reverse phase High Performance Liquid Chromatography on cyanopropyl-modified silica stationary phase, containing lipophilic and polar moieties, is used. While passing through the column among with the mobile phase the test substance interacts with the stationary phase. As a result of the partitioning between the mobile and stationary phase the test substance is retained. The dual-composition of the stationary phase having polar and non-polar sites allows for interaction of polar and non-polar groups of a molecule in a similar way as it is the case for organic matter in soil or sewage sludge matrices. This enables the relationship between the retention time on the column and the adsorption coefficient on organic matter to be established.

Conclusion

The chromatograms of Benzyl Salicylate show one peak at an average retention time of 12.52 minutes, corresponding to an adsorption coefficient (log value) of 3.75. Therefore: Adsorption coefficient (Koc) of Benzyl Salicylate: log Koc = 3.75

Description of key information

Based on GLP study following OECD 121, log Koc is 3.75 (Koc = 5623 L/kg).

Key value for chemical safety assessment

Koc at 20 °C:
5 623

Additional information

The chromatograms of Benzyl Salicylate show one peak at an average retention time of 12.52 minutes, corresponding to an adsorption coefficient (log value) of 3.75. Therefore, adsorption coefficient (Koc) of Benzyl Salicylate: log Koc = 3.75, equivalent to a Koc of 5623.