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Partition coefficient

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Reference
Endpoint:
partition coefficient
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2016
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
Guideline study performed under GLP. All relevant validity criteria were met.
Qualifier:
according to
Guideline:
OECD Guideline 117 (Partition Coefficient (n-octanol / water), HPLC Method)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method A.8 (Partition Coefficient)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Remarks:
inspected June 2013; signature: November 2013
Type of method:
HPLC method
Partition coefficient type:
octanol-water
Analytical method:
high-performance liquid chromatography
Type:
log Pow
Partition coefficient:
>= 2.71 - <= 6.86
Temp.:
22.3 °C
pH:
ca. 7
Remarks on result:
other: Two chromatographically resolved peaks corresponding to the above log Pow range of the test item.

HPLC method

The mean void time (t0) was determined to be 0.485 minutes.

The results of the HPLC method are given in the Table 3. The calibration curves of the log k’ of the reference substances as function of log Pow had an regression line represented by the equations:

Calibration 1: log Pow = 3.709 × log k’+ 0.0761 (r = 0.9906, n = 20 and r2 = 0.9812).

Calibration 2: log Pow = 3.816 × log k’+ 0.0724 (r = 0.9905, n = 20 and r2 = 0.9811).

 

Table 2. Calibration data

Reference item

log POW

1st Calibration

2nd Calibration

tR1
[min]

k

log k

tR2
[min]

k

log k

Ethyl benzoate

2.6

  2.727

  4.62

0.665

  2.727

  4.62

0.665

Chlorobenzene

2.8

  3.304

  5.81

0.764

  3.308

  5.82

0.765

Allyl phenyl ether

2.9

  3.182

  5.56

0.745

  3.187

  5.57

0.746

Ethylbenzene

3.2

  4.459

  8.19

0.913

  4.463

  8.20

0.914

Phenyl benzoate

3.6

  4.056

  7.36

0.867

  4.059

  7.37

0.867

Biphenyl

4.0

  5.804

11.0  

1.04  

  5.805

11.0  

1.04  

n‑Butylbenzene

4.6

  9.833

19.3  

1.29  

  9.839

19.3  

1.29  

Triphenylamine

5.7

16.683

33.4  

1.52  

16.694

33.4  

1.52  

DDT

6.5

24.014

48.5  

1.69  

24.052

48.6  

1.69  

tR1: Retention time 1. Injection

tR2: Retention time 2. Injection

k: Capacity factor reference item

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

 

Table 3. Test item determination

First signal
(lowest retention time)

tR [min]

k

log k

log POW

1st Calibration

2nd Calibration

2.969

5.12

0.709

2.71 ± 0.09
2.48 to 2.93 (95 % CI)

2.70 ± 0.10
2.48 to 2.93 (95 % CI)

2.970

5.12

0.709

Mean

2.970

5.12

0.709

2.71

Last signal
(highest retention time)

tR [min]

k

log k

log POW

1st Calibration

2nd Calibration

32.948

66.9

1.83

6.86 ± 0.16
6.48 to 7.25 (95 % CI)

6.86 ± 0.17
6.47 to 7.26 (95 % CI)

32.902

66.8

1.82

Mean

32.925

66.9

1.83

6.86

tR : Retention time

k : Capacity factor test item

POW : Partition Coefficient (n-octanol / water)

CI : Confidence Interval

 

Additional comments:

For the signal with the lowest retention time, an individual log POW value of 2.71 ± 0.09 (95 % CI 2.48 to 2.93) was obtained with the first and of 2.70 ± 0.10 (95 % CI 2.48 to 2.93) with the second calibration curve. The individual values did not differ more than ± 0.1 log POW units. Based on these data a mean log POW value of 2.71 was derived. For the last signal with the highest retention time, an individual log POW value of 6.86 ± 0.16 (95 % CI 6.48 to 7.25) was obtained with the first and of 6.86 ± 0.17 (95 % CI 6.47 to 7.26) with the second calibration curve. The individual values did not differ more than ± 0.1 log POW units. Based on these data a mean log POW value of 6.86 was derived. These values needed to be extrapolated, as they outranged the calibration range.

Conclusions:
The partition coefficient of the test substance was determined to be in the range log Pow = 2.71 to 6.86 at 22.3 °C and ca. pH 7.0
Executive summary:

The n-octanol-water partition coefficient was determined using the HPLC method of OECD Method 117 and EU Method A.8. The test was performed with a concentration of 100 mg test item/L in 60 % acetonitrile : 40 % HPLC water. Samples of the test item were analysed via HPLC on a C18 column with diode array detection. Calibration was performed using ten reference items with known log POW values (given by the guidelines). The reference items were measured twice, once before and once after the measurement of the test item, for which one replicate was double injected. The void time of the HPLC system was determined with sodium nitrate. Multiple chromatographic signals were observed for the test item. In order to address the log POW range, the signals with the lowest and highest retention times were evaluated. Two individual log POW values for the test item were derived under consideration of the first and second calibration and finally, a mean value was calculated from these individual log POW values for the first and the last chromatographically resolved signal of the test item with the lowest and highest retention time, respectively. Based on these data, the log POW of the test item was determined to be in the range of 2.71 to 6.86 at mean temperature 22.3 °C and approximately neutral pH.

Description of key information

log Pow = range: 2.71 - 6.86 at 22 ± 1 °C, OECD TG 117, 2016

Key value for chemical safety assessment

Additional information

The n-octanol-water partition coefficient was determined using the HPLC method of OECD Method 117 and EU Method A.8. The test was performed with a concentration of 100 mg test item/L in 60 % acetonitrile : 40 % HPLC water. Samples of the test item were analysed via HPLC on a C18 column with diode array detection. Calibration was performed using ten reference items with known log POW values (given by the guidelines). The reference items were measured twice, once before and once after the measurement of the test item, for which one replicate was double injected. The void time of the HPLC system was determined with sodium nitrate. Multiple chromatographic signals were observed for the test item. In order to address the log POW range, the signals with the lowest and highest retention times were evaluated. Two individual log POW values for the test item were derived under consideration of the first and second calibration and finally, a mean value was calculated from these individual log POW values for the first and the last chromatographically resolved signal of the test item with the lowest and highest retention time, respectively. Based on these data, the log POW of the test item was determined to be in the range of 2.71 to 6.86 at mean temperature 22.3 °C and approximately neutral pH.