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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:
7 January 2012 - 10 March 2012
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Remarks:
This study was considered as reliable with restrictions because it was not conducted under GLP and there are some lack of details in the study report.
Reason / purpose:
reference to same study
Reason / purpose:
reference to other study
Qualifier:
according to
Guideline:
EU Method A.8 (Partition Coefficient)
Deviations:
no
Qualifier:
according to
Guideline:
OECD Guideline 117 (Partition Coefficient (n-octanol / water), HPLC Method)
Version / remarks:
(13 April 2004)
Deviations:
no
GLP compliance:
not specified
Type of method:
HPLC method
Partition coefficient type:
octanol-water
Analytical method:
high-performance liquid chromatography
Key result
Type:
log Pow
Partition coefficient:
ca. 2.76
Temp.:
30 °C
pH:
ca. 6.5
Remarks on result:
other: +/-0.01

REFERENCE ITEMS :

Retention times and capacity factors

The retention times of the reference items and calculated capacity factors are presented in the following table.

Compound tR1(min) tR2(min)  Mean (min)  Standard deviation (min) Relative standard deviation k
Benzene  3.77  3.77  3.77  0.00  0.00% 0.47
Trichloroethylene  4.42  4.43  4.43  0.01  0.16% 0.73
Toluene  4.79  4.77  4.78  0.01  0.30%  0.86
M-Xylene  6.58  6.57  6.58  0.01  0.11%  1.56
1,2,4-trimethylbenzene  9.17  9.15  9.16  0.01  0.15%  2.57
Benfuracarb  10.51  10.47  10.49  0.03  0.27%  3.02
Butralin  19.50  19.49  19.50  0.01  0.04%  6.60
Heptachlor  27.13  27.13  27.13  0.00  0.00%  9.58

The relative standard deviations of the retention times of the reference items laid all below 0.3%.

Dead times t0:

- 2.56 and 2.57 min (HPLC analysis of reference items mix)

- 2.61 and 2.61 min (HPLC analysis of Benfuracarb).

The mean value is used for calculation of k.

log Pow/log k

log Pow (literature data) and calculated log k of the reference items are presented in the following table.

Compound log k log Pow
Benzene -0,33 2,13
Trichloroethylene -0,14 2,4
Toluene -0,06 2,69
M-Xylene 0,19 3,16
1,2,4-trimethylbenzene 0,41 3,65
Benfuracarb 0,48 4,22
Butralin  0,82 4,93
Heptachlor  0,98 5,44

log k versus log Pow and Correlation Results

The logarithms of the mean capacity factors, log k, are plotted as a function of log Pow and the linear regression equation is obtained as follows :

log k = (0.383 x log Pow) - 1.075

with a coefficient of determination r2 = 0.986

TEST ITEM NEROL

Retention times and capacity factors

The retention times of the test item are presented in the following table.

  tR1(min) tR2(min) tR3(min)  Mean (min)  Relative standard deviation
Test item 5,03 5,03 5,03 5,03 0,00%
Dead time 2,57 2,57 2,58 2,57 0,22%

log Pow/log k

Log Pow is calculated using the regression equation obtained from the reference items.

Capacity factor k, log k and log Pow for the test item are presented in the following table.

Measurement No. k log k log Pow
1 0,96 -0,02 2,76
2 0,96 -0,02 2,76
3 0,95 -0,02 2,75
Mean     2,76
Standard deviation     0,01

Results obtained with another HPLC Column

The retention times and capacity factors of the reference items obtained with a different C18 bonding are presented in the table below.

Compound tR(min) k log k
Benzene 4,09 0,83 -0,08
Trichloroethylene 5,13 1,3 0,11
Toluene 5,63 1,52 0,18
M-Xylene 8,35 2,74 0,44
1,2,4-trimethylbenzene 12,19 4,47 0,65
Benfuracarb 20,17 8,04 0,91
Butralin  37,29 15,72 1,2
Heptachlor  47,55 20,32 1,31

The linear regression of the plot log k versus log Pow gives the following equation:

log k = (0.425 x log Pow) – 0.931

with a coefficient of determination r² = 0.992

The retention time of the test item was 6.59 min, corresponding to a log k of 0.29. According to the previous equation, the log Pow can be estimated to 2.88 with this column.

This result is not significantly different from the one obtained previously (2.76). It can be concluded that a change in the C18 silica bonding chemistry has no significant effects on log Pow results.

Conclusions:
Using the HPLC method, log Pow of nerol was determined to be 2.76 ± 0.01
Executive summary:

Partition coefficient of nerol was determined at 30°C by the HPLC method, according to EC A8 guideline and OECD guideline 117.

log Pow = 2.76 ± 0.01 (Mean retention time: 5.03 min). This value was the mean ± standard deviation of three independent determinations.

Calibration was appropriately performed between 2.13 and 5.44, in buffered mobile phase at pH=6.5, with 8 references substances. These reference items were chosen in relation to the expected retention time of the test item. For each reference item, two determinations were performed. The capacity factor k was calculated from the retention time of acetone (dead time) and the retention time of the respective reference item. A calibration function (log k versus log Pow, linear fit) was determined based on literature values of Pow for the reference items. Despite the purity of the references substances was missing, the regression equation shows a good linearity. The correlation between log k and log Pow was satisfactory according to the coefficient of determination r² of 0.986. This value was considered as sufficiently high to use the calibration function for the determination of the log Pow of test item nerol. Variations in the retention times of reference items and test item were very small. Therefore a stable configuration of the HPLC-column can be assumed.

A second measurement was carried out on another C18 silica column and gave similar results.

As no observations were made which might cause doubts concerning the validity of the study outcome, the study was considered as reliable without restriction.

The log Pow of nerol being below 3, a low potential for bioaccumulation was shown.

Description of key information

Using the HPLC method, log Pow of nerol was determined to be 2.76 ± 0.01. 
Therefore, nerol shows a low potential for bioaccumulation.

Key value for chemical safety assessment

Log Kow (Log Pow):
2.76
at the temperature of:
30 °C

Additional information

The partition coefficient of nerol was determined by High Performance Liquid Chromatography method according to guidelines OECD 117 and EC A8. No observations were made which might cause doubts concerning the validity of the study outcome. Therefore, the well described result can be used as key value for the partition coefficient of nerol.

Based on the log Kow result, nerol shows a low potential for bioaccumulation.