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Partition coefficient

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partition coefficient
Type of information:
other: experimental result obtained on one of the main constituents
Adequacy of study:
key study
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
according to
OECD Guideline 117 (Partition Coefficient (n-octanol / water), HPLC Method)
Due to technical reasons standards were injected separately instead of simultaneously. This had no influence on the quality or the scientific integrity of the study
other: EU Method A.24 (Partition Coefficient)
due to technical reasons standards were injected separately instead of simultaneously. This had no influence on the quality or the scientific integrity of the study
GLP compliance:
yes (incl. certificate)
Type of method:
HPLC method
Partition coefficient type:
Analytical method:
high-performance liquid chromatography
Key result
log Pow
Partition coefficient:
23.6 °C
Remarks on result:
other: weighted average mean value
Key result
log Pow
Partition coefficient:
23.6 °C
Remarks on result:
other: for the first signal (4-phenylethylphenol)
Key result
log Pow
Partition coefficient:
23.6 °C
Remarks on result:
other: for the second signal (2-phenylethylphenol)
Details on results:
- Temperature: mean temperature during experimental phase was within the range of 20 - 25°C +/- 1°C during the study; min.: 23.4; max. 23.7°C.
- Signal-to-noise ratio: for the void time marker, reference items and test item > 3
- Determination of void time (t0): mean after threefold injection of 10 mg/L NaNO3, t0 = 0.750 (min)

Calculation of the weighted average mean value

log Pow Area (%)
1 st Calibration 2nd Calibration Mean

Signal 1:

4-(1 -phenylethyl) phenol

3.00 ± 0.05
 2.87 to 3.14 (95% CI)
2.98 ± 0.05
2.84 to 3.12 (95% CI)
2.99 73.0

Signal 2:

2-(1 -phenylethyl) phenol

3.14 ± 0.05
3.00 to 3.27 (95% CI)
3.12 ± 0.05
2.98 to 3.26 (95% CI)
3.13 27.0
 Weighted Mean  3.03

Calibration data of the reference items

Reference item log Pow 1st Calibration 2nd Calibration
tR1 (min) k log k tR2 (min) k log k
Benzonitrile 1.6 1.851 1.470 0.167 1.885 1.510 0.180
Nitrobenzene 1.9 2.682 2.580 0.411 2.735 2.650 0.423
Toluene 2.7 6.042 7.060 0.849 6.199 7.270 0.861
Ethylbenzene 3.2 9.489 11.700 1.070 9.742 12.000 1.080
Thymol1 3.3
Isopropylbenzene 3.7 14.224 18.000 1.250 14.501 18.300 1.260
Biphenyl 4.0 17.645 22.500 1.350 17.903 22.900 1.360
1,2,4-Trichlorobenzene  4.2 20.333 26.100 1.420 20.496 26.300 1.420

tR1: Retention time 1st injection

tR2: Retention time 2nd injection

k: Capacity factor reference item

log Pow: Common logarithm of the Partition Coefficient (n-octanol / water)

1: determined to be an outlier via F-test for both calibrations

The partition coefficient log Pow of the test chemical was determined at 23.6°C.
4-Phenylethyl phenol was found to have a log Kow of 2.99.
2-Phenylethyl phenol was found to have a log Kow of 3.13.
Executive summary:

The test was performed to determine the partition coefficient (n-octanol / water) of the test item according to OECD TG 117 and EU Method A.24 and in compliance to GLP. The test chemical contains 30.7% of 2-phenylethyl phenol and 67.5% of 4-phenylethyl phenol. The test was performed with a concentration of approx. 20 mg/L test item in 65% methanol: 35% HPLC water. Samples of the test item were analysed via HPLC on a C18 column with diode array detection. Calibration was performed using seven reference items with known log Pow values. The reference items were measured twice, once before and once after the measurement of the test item. The void time of the HPLC system was determined with sodium nitrate. For each of the two test chemical signals, two individual log Pow values were derived under consideration of the first and second calibration and a mean value was calculated from these individual log Pow values. The mean column temperature was determined to be 23.6°C during the study. The identity of the two test item signals was based on the respective peak area and composition as specified. All validity criteria were fulfilled. The partition coefficient log Pow of the test item was determined at 23.6°C to be 2.99 for the first signal (4-phenylethylphenol) and 3.13 for the second signal (2-phenylethylphenol). The weighted average mean value is 3.03. both calibrations.

Description of key information

The n-­octanol/water partition coefficient (log Kow) of 4-­monostyryl phenol (4-­MSP) and 2-monostyryl phenol (2-­MSP) was determined by means of the HPLC method in accordance with OECD Guidance 117 and EU method A.24.This method was found appropriate and adequate notwithstanding the fact that 4-­MSP was found to be to a certain extent surface active.

The used test material consisted of a mixture containing 30.7% 2-­MSP and 67.5% 4-­MSP. The HPLC analysis used a C18 column with diode array detection. Under the selected HPLC conditions, the test material provided two non-­overlapping signals, which allowed for the determination of an individual Log Kow value for both isomers. 4 ­MSP was found to have a log Kow of 2.99, and the Log Kow of 2-­MSP was found to be 3.13.

Key value for chemical safety assessment

Log Kow (Log Pow):
at the temperature of:
23.6 °C

Additional information

Two mono-­styrenated phenol isomers are present in the registered substance: 2-­monostyryl phenol (2 ­MSP) and 4-­monostyryl phenol (4 ­MSP). For the purpose of the PBT and exposure assessments, it is critical to obtain individual octanol-­water partition coefficients for these isomers. For this purpose, the HPLC method (OECD 117) is the most appropriate choice. The different stereo-­isomers are separated during the chromatography, which will allow for the determination of individual log Kow values for both constituents.

However, according to OECD guideline 117, the HPLC method is not applicable to surface active agents, while the surface tension test performed on 4-­MSP indicated that 4-­MSP has some surface active potential. It has nevertheless to be taken into account that the surface tension value of 4 ­MSP – even though being below the 60 mN/m threshold – still is quite high as compared to that of “true surfactants”. The surface activity of 2-­MSP is expected to be even less. It is therefore deemed unlikely that 4-­MSP and 2-­MSP will behave as true surface active substances.

Hence it is anticipated that the advantage of obtaining individual log Kow values outweighs the risk of technical problems in the HPLC test due to surface activity of the substances. This is further substantiated by the fact that thymol – one of the reference substances used in the HPLC method – has a number of structural characteristics in common with MSP: one hydroxyl group as the only hydrophilic group, and a carbon-­substituted benzene ring as the hydrophobic moiety.

The applicability of the HPLC method for the determination of the log Kow value for 2-MSP and 4 ­MSP is confirmed post factum as the chromatogram of the test item run shows sharp peaks that are adequately separated.