2,4-diethyl-9H-thioxanthen-9-one

Adsorption / desorption

Link to relevant study record(s)

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

GLP compliance:

yes (incl. QA statement)

Type of method:

HPLC estimation method

Media:

soil/sewage sludge

Test temperature:

25 ± 0.5 °C

Details on study design: HPLC method:

TEST SYSTEM

1) Analytical Instrument HPLC
a) Components:
- Pump M480 G
- Degasser Gastorr AG-34-01
- Autosampler ASI-100
- Column thermostat DIONEX TCC-100
- 6 fold column switch valve i-Valve
- UV/VIS-Detector UVD 170U
b) Manufacturer:
- Pump: Gynkotek,
- Degasser: FLOM
- all other components: DIONEX, Idstein;
c) Software: CHROMELEON 6.8 SR11d, Build 3302

2) Method parameters HPLC
- Column: Reprosil-PUR 120 CN 125*4.6 mm, Dr. A. Maisch, Part Number R13.CE.S1246, SN 50916 376016, with pre-column Phenomenex SecurityGuard CN, 4x3 mm
- Eluent: isocratic methanol/water 55/45 (% v/v), degassed
- Flow rate: 0.8 mL/min
- Injection volume: 10 µL
- Column temperature: 25 °C
- Wavelength, used for evaluation: 220 nm

3) Reference substances
The substances which have been chosen (taking into account the retention time of the test item DETX) are presented hereinafter; the reference items were dissolved in the mobile phase:
- Sodium nitrate (CAS# 7631-99-4) >= 99.5 %; concentration injected: 1.5 mg/L
- Phenol (CAS# 108-95-2) >= 99.0 %; concentration injected: 1.5 mg/L
- Methyl benzoate (CAS# 93-58-3) >= 99.5 %; concentration injected: 1.5 µg/L
- Naphthalene (CAS# 91-20-3) >= 99.7 %; concentration injected: 1.0 mg/L
- 1,2,3-Trichlorobenzene (CAS# 87-61-6) 99.0 %; concentration injected: 4.0 mg/L
- Phenanthrene (CAS# 85-01-8) 99.5 %; concentration injected: 3.0 mg/L
- 4,4'-DDT (CAS# 50-29-3) 98.7 %; concentration injected: 10.0 mg/L

4) Chemicals
All chemicals used in the test were "analytical grade" or otherwise proved suitable.
- Water: Demineralised Water, HPLC-grade, giving no interferences with the detector signal. Deionised water was also used.
- Methanol: CH3OH, HPLC grade, giving no interferences with the detector signal.
- Mobile Phase: A mixture of 55% methanol and 45% water, isocratic, was used. The mobile phase was produced by mixture of 225 mL water and 275 mL methanol. pH of the eluent was 5-6 (measured with pH paper). The temperature was held constant at 25 ±0.5 °C by use of a HPLC column oven.
- Test Item Solution: A solution of the test item was prepared by weighing 20.5 mg DETX into a 20 mL flask and filling up to 20.5 mL with methanol, resulting in a solution with nominal concentration 1 g/L. 0.05 mL of this solution were filled up to 5.0 mL with mobile phase, resulting in a solution with a concentration of 10 mg/L which was used for the measurements of the pre-test and of the main test.

Key result

Type:

log Koc

Value:

4.438 - 4.442

Temp.:

25

Remarks on result:

other: pH of the eluent was 5-6 (measured with pH paper)

Details on results (HPLC method):

- Retention times of reference substances used for calibration: see 'Any other information on results incl. tables'
- Details of fitted regression line (log k' vs. log Koc): see 'Any other information on results incl. tables'
- Graph of regression line attached
- Average retention data for test substance: see 'Any other information on results incl. tables'

Reference Items

1) Measurement data

The retention times which were found for the reference items are presented in the following table:

Compound	RT1	RT2	RT3	RT4	RT5	RT6
	min.	min.	min.	min.	min.	min.
Sodium nitrate	1.333	1.244	1.225	1.176	1.171	1.163

Phenol	2.996	2.996	2.999	3.008	3.003	3.005
Methylbenzoate	3.342	3.339	3.348	3.354	3.349	3.353
Naphthalene	5.189	5.189	5.211	5.217	5.211	5.221
1,2,3-Trichlorobenzene	6.335	6.338	6.368	6.373	6.369	6.379
Phenanthrene	9.251	9.267	9.326	9.346	9.340	9.346
4,4’-DDT	24.537	24.725	24.848	24.991	24.957	24.992

Table 1: Retention Times (RT) reference items

2) Calculated values

The capacity factors k’ were calculated from the retention times using the equation k' = t_r- t₀/ t₀

The values are given in the following table:

Compound	RT Mean	RT Stand. Dev.	RT Relative Stand. Dev.	k’
	min.	min.	%
Sodium nitrate	1.219	0.065	5.297	0.0000
Phenol	3.001	0.005	0.167	1.4626
Methylbenzoate	3.348	0.005	0.181	1.7469
Naphthalene	5.206	0.014	0.264	3.2722
1,2,3-Trichlorobenzene	6.360	0.019	0.295	4.2190
Phenanthrene	9.312	0.043	0.458	6.6414
4,4’-DDT	24.842	0.182	0.731	19.3842

Table 2: Mean Retention Times, Capacity Factors reference items

3) log Koc / log k'

The log Koc values of the reference items were taken from the guideline. The values for log k' and log Koc of the reference items are presented in the following table:

Compound	log k’	log KOC
Phenol	0.1651	1.32
Methylbenzoate	0.2423	1.80
Naphthalene	0.5148	2.75
1,2,3-Trichlorobenzene	0.6252	3.16
Phenanthrene	0.8223	4.09
4,4’-DDT	1.2874	5.63

Table 3: Log k' and log Koc of Reference Items

4) Correlation results

Dead time is 1.219 ± 0.065 minutes, with a RSD of 5.3%.

Equation of the regression: log k' = 0.2612 * logKoc - 0.2066

with a coefficient of determination r2 = 0.9961.

Test Item DETX

1) Pre-Test

In the preliminary test, a solution of the test item with a concentration of 10 mg/L was injected in order to check retention time and the signal height. The solution gave one peak at 11.7 minutes.

Based on this result, a suitable mix of reference items was chosen (with DDT as substance with the highest log Koc and a retention time of approx. 23.7 minutes). The test item solution with concentration of 10 mg/L was used for the determination of the log Koc of the test item.

Initially, the measurement (pre-test) failed. After the column was replaced by another column and rinsed several times, the measurement was good and can be evaluated.

2) Measurement data

The retention times (RT) of the peaks are presented hereinafter:

- RT _{Measurement 1}: 12.139 min

- RT_{Measurement 2}: 12.168 min

- RT_{Measurement 3}: 12.149 min

- RT_Mean: 12.152 min

- Standard deviation: 0.014 min

3) Calculated values

The calculated values are presented in the following table:

	k'	log k'	log Koc
Measurement 1	8.9609	0.9524	4.438
Measurement 2	8.9843	0.9535	4.442
Measurement 3	8.9691	0.9527	4.439
Mean			4.440
Standard deviation			0.002

Table 4: Capacity Factor, log Capacity Factor, log Koc Test Item

log Koc was calculated from the capacity factor as follows: log Koc = (log k' + 0.2066) / 0.2612

4) Results and validity

The correlation log k'/log Koc is sufficiently accurate, as calibration gave a coefficient of determination r²= 0.9961.

Using the correlation log k' / log Koc, the log Koc of the peak of the test item DETX was calculated as 4.440 ± 0.002 (mean ± standard deviation).

No observations were made which might give doubts concerning the validity of the study outcome; the validity criteria were fulfilled:

- range (max - min. log Koc): 0.004 (criterion < 0.25)

- result within calibration range of reference items: 4.440 (criterion 1.32 - 5.63)

Validity criteria fulfilled:

yes

Conclusions:

estimated log Koc: 4.440 ± 0.002

Executive summary:

The study was performed according to OECD Guideline 121, 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.

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 = 0.996.

The chromatogram of the test item gave one peak (mean retention time = 12.152 min). The test item DETX has an estimated log Koc of 4.440 ± 0.002 (mean ± standard deviation).

Description of key information

estimated log Koc at 25 °C (determined using OECD 121; GLP): 4.440 ± 0.002

Key value for chemical safety assessment

Koc at 20 °C:

27 542

Additional information

The substance DETX has a high adsorption/desorption coefficient (LogKoc = 4.44 at 25°C), which indicates that it will have high likelihood of partitioning to sediments, organic matter in soil or sludge in the sewer system.

[LogKoc: 4.44]