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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:
15-23 December 1993
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Study conducted by a GLP accredited laboratory. Method according to OECD guideline.
Qualifier:
according to
Guideline:
OECD Guideline 117 (Partition Coefficient (n-octanol / water), HPLC Method)
GLP compliance:
yes
Type of method:
HPLC method
Partition coefficient type:
octanol-water
Analytical method:
high-performance liquid chromatography
Key result
Type:
log Pow
Partition coefficient:
5.7
Temp.:
24 °C
Remarks on result:
other: pH not mentioned
Details on results:
Retention times were measured and capacity factors (k) calculated. The Log Kow of the reference substances was plotted versus log (k). The result was a straight line and linear regression described the linear relationship: Log Kow = 3.678 log (k) + 2.598.

Table I Retention times and capacity factors of the reference substances and the test substance.

Log Kow tR average k log k
Reference substances
Thiourea 1.33
Aniline 0.9 1.80 0.358 -0.446
Acetophenone 1.7 2.06 0.555 -0.256
Benzophenone 3.2 3.15 1.374 0.138
Naphthalene 3.6 3.66 1.758 0.245
1,2,4-trichlorobenzene 4.2 5.42 3.087 0.490
n-butylbenzene 4.6 6.38 3.815 0.581
triphenylamine 5.7 9.72 6.332 0.802
Conclusions:
The partition coefficient n-octanol/water (log value) determined with reversed-phase HPLC is 5.7
Executive summary:

The partition coefficient n-octanol/water has been determined by the reverse phase high performance liquid chromatographic method. The result is log Kow = 5.7. This value was determined on the basis of the retention times of references substances with known partition coefficients. Retention time can be correlated to capacity factors. The reference substances showed a linear relationship between the logarithm of the partition coefficient ( log(Kow) ) and the capacity factor (k). Log Kow of AHTN was determined after applying linear regression on the reference substances.

Description of key information

A log Kow of 5.4 has been reported in a thesis (Artola-Garicano 2002) where the slow stirring method has been used. A more formal partition coefficient determination on the basis of HPLC has been measured by a GLP compliant laboratory using OECD method 117. The value obtained from the slow-stirring method has been leading in the EU Risk Assessment Report of the test item (May 2008).

Key value for chemical safety assessment

Log Kow (Log Pow):
5.4
at the temperature of:
25 °C

Additional information

A log Kow of 5.4 was selected for the environmental risk assessment in the EU Risk Assessment Report of AHTN (EU RAR). However, for the purpose of REACH, the underlying source was a thesis from a doctoral student without any raw data. The EU RAR did not substantiate this particular log Kow selection. The log Kow is an important parameter and the reported value is not regarded as sufficiently reliable without a supporting study. Hence a supporting study has been included in the test item registration, which is a reversed phase HPLC experiment (Rudio 1993). The partition coefficients from Artola and Rudio differ 0.3 log units, which is even within the range of the repeatability of the shake-flask method. On that basis, a log Kow of 5.4 is acceptable and selected on the basis of consistency with the EU RAR.