Paraffin waxes (Fischer-Tropsch), isomerization

Partition coefficient

Link to relevant study record(s)

Reference

Endpoint:

partition coefficient

Type of information:

experimental study

Adequacy of study:

key study

Study period:

16 May 2008 and 02 September 2008

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method A.8 (Partition Coefficient)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

Date of inspection: December 2002; Date of certificate: February 2003

Type of method:

HPLC method

Partition coefficient type:

octanol-water

Analytical method:

high-performance liquid chromatography

Type:

Pow

Partition coefficient:

> 3.16

Temp.:

40 °C

pH:

ca. 7

Details on results:

Results:
Preliminary estimate:
Approximate solubility in n-octanol: 6.18 E2 g/l
Approximate solubility in water:      <8.40 E-3g/l
Approximate Pow:  >7.35 E4
Log10Pow:  >4

Approximate solubility in n-octanol: >1.00 E3 g/l
Aproximate solubility in water: <1.50 E-3 g/l
Approximate Pow: >3.16 E6,
Log10 Pow: >6.50

results from definitive test:
Mean Log Pow: >6.50
Partition coefficient:>3.16 E6.

Results:

Preliminary estimate:

Approximate solubility in n-octanol: 6.18 x 10² g/l
Approximate solubility in water:      <8.40 x 10^-3g/l
Approximate P_ow:  >7.35 x 10⁴
Log₁₀P_ow:  >4

Definitive test:

Calibration

The retention times of thiourea and the retention times, capacity factors (k) and log₁₀P_owvalues for the reference standards are shown in the following tables:

Dead Time	Retention Time (mins)		Mean Retention Time (mins)
	Injection 1	Injection 2
Thiourea	2.707	2.712	2.710

Standard	Retention Time (mins)		Mean Retention Time (mins)	Capacity Factor (k)	Log10k	Log10Pow
	Injection 1	Injection 2
Benzene	4.419	4.418	4.419	0.631	-0.200	2.1
Toluene	4.879	4.876	4.878	0.800	-9.68 x 10^-2	2.7
Naphthalene	4.690	4.689	4.690	0.731	-0.136	3.6
Phenanthrene	4.930	4.928	4.929	0.819	-8.66 x 10^-2	4.5
Triphenylamine	6.189	6.189	6.189	1.28	0.109	5.7
DDT	7.699	7.700	7.700	1.84	0.265	6.5

Discussion:

Substances having a log₁₀P_owgreater than 3 are regarded as having the potential to bioaccumulate in the environment.

The test material was known to primarily be a complex mixture of alkanes and therefore a majority of the components were not anticipated to absorb in the ultraviolet region. As no components were successfully eluted from the HPLC column using isocratic conditions maintaining a minimum of 25% water in the mobile phase as required by EEC Method A.8, it was necessary to introduce a gradient increase in the solvent content on the mobile phase to 100% tetrahydrofuran. This requirement eliminated the viability of refractive index detection as the detector baseline is adversely affected by the continuing shift in the refractive index of the mobile phase caused by the gradient. Therefore the sample was monitored in the UV region and the elution of the test material confirmed by fraction collection and subsequent GC analysis.

The retention time limit value used for the calculation of the sample partition coefficient result represents the start of the amended 100% tetrahydrofuran mobile phase. All components of the test material were demonstrated to elute after this time and shared a common partition coefficient value, that of greater than the highest calibration standard.

In the absence of any dissociating groups, the test material being a mixture of alkanes, no manipulation of the mobile phase pH was necessary to ensure the molecular form of each component. Therefore the determination was performed at approximately neutral pH.

Conclusions:

The partition coefficient of the test material has been determined to be > 3.16 E6, log Pow >6.50.

Executive summary:

The partition coefficient of the substance GTL waxy raffinate ['Paraffin waxes (Fischer-Tropsch), full range, C15-50- branched and linear'] was determinated using the HPLC Method, Method A.8 of Commission Directive 92/69/EEC (which constitutes Annex V of council directive 67/548/EEC). Under the conditions of the test, the test material was determined to have a partition coefficient of > 3.16 x 10⁶, and a log Pow >6.50.

The limit value of 6.5 is based on the retention time of the reference substance DDT.

Description of key information

- partition coefficient of the closely related substance GTL waxy raffinate [C15-50; CAS 848301-87-1, EC 482-130-1] covering the low molecular weight fraction of the registration substance up to C50 [determined using EU Method A.8, HPLC method]: greater than 3.16 x 10⁶, log₁₀ K_OW >6.50 (arithmetic mean of two determinations at 40°C and pH 7);

- based on the general trend of decreasing water solubility with increasing carbon chain length/molecule size and the fact that the experimentally determined value for GTL waxy raffinate is based on the highest calibration standard [DDT, limit value of 6.5], it can be safely concluded that the result for the registration substance 'Paraffin waxes (Fischer-Tropsch), isomerization' containing higher molecular weight constituents (C25 - C150, about 30-55 % >C50) would be the same: 3.16 x 10⁶, log₁₀ K_OW >6.50.

Key value for chemical safety assessment

Log Kow (Log Pow):

6.5

at the temperature of:

40 °C

Additional information

Measured data are not available for the registration substance itself.

However, reliable data of the closely related substance GTL waxy raffinate (C15-50; CAS 848301-87-1, EC 482-130-1) can be used to address the endpoint, which is suitable to draw conclusions on the partition coefficient of the registration substance.
The test item GTL waxy raffinate - consisting of linear and branched alkanes (paraffins) in the carbon range from C15 to C50 - covers the entire low molecular weight fraction of the registration substance up to C50. Based on the general trend of decreasing water solubility with increasing carbon chain length/molecule size and the fact that the experimentally determined value for this substance is based on the highest calibration standard [DDT, limit value of 6.5], it can be safely concluded that the experimental result for the registration substance containing higher molecular weight constituents (C25 - C150, about 30-55 % >C50) would be the same: greater than 3.16 x 10⁶, log₁₀ K_ow >6.50.

The conclusion is supported by the identical test result for the closely related substance GTL base oil (CAS 848301-69-9, EC 482-220-0), which consists of linear and branched alkanes (paraffins) with a small proportion of cycloalkanes in the carbon range from C18 to C50; see supporting study).

 

Predicted log Kow values, calculated using a validated QSAR method, are available for individual constituents of the substance GTL waxy raffinate (C15-50; CAS 848301-87-1, EC 482-130-1). Predictions are in the range log Kow 7.71 to >9.0. Based on the identical predicted results for individual constituents in the carbon range, C30-50, a log Kow of >9 can also be considered for the higher molecular weight constituents of the registration substance (>C50).