Sodium bis[3-[[1-(3-chlorophenyl)-4,5-dihydro-3-methyl-5-oxo-1H-pyrazol-4-yl]azo]-4-hydroxybenzenesulphonamidato(2-)]cobaltate(1-)

Partition coefficient

Description of key information

Log Pow = 3.117 +/- 0.007 

Key value for chemical safety assessment

Log Kow (Log Pow):

3.117

at the temperature of:

25 °C

Additional information

Partition coefficient was determined by OECD Guideline 117 (Partition Coefficient (n-octanol/water), HPLC Method).

The study was performed using a HPLC with a C18 column. Seven reference substances with different retention times and thiourea for the determination of the dead time were used to produce a calibration curve, since retention time on hydrophobic columns and Pow are correlated. The reference substances were chosen consequent to the pre-test.

One vial was filled with the reference substance mix and one vial with the test substance solution. The vials were analysed using the HPLC with the program described above. One injection from the solvent blank methanol/water 65/35 (%v/v) was made. Three injections were measured from the reference substance mix, three injections from the test substance and again, three injections from the reference substance mix.

For each reference substance, the capacity factor, K, was calculated from the retention time of thiourea and the retention time of the respective reference substance. A calibration function (log K versus log Pow, linear fit) was determined using the literature

values for Pow of the reference substances and the retention times in the six determinations.

The chromatogram of the test substance gave one small peak at 1.0 min in the dead time of the method and a large broad peak at 8.8 min. The retention time of peak 1 lay below the retention time of thiourea. The reason for this lower retention time may be, that a

charged molecule is repelled by unmodified silanole groups of the HPLC column material and therefore, elutes before the dead time.

With the calibration function log K versus log Pow, the corresponding log Pows of the peaks were determined with:

Peak 1: log Pow <0.3

Peak 2: log Pow 3.117 +/- 0.007

These values are the means i standard deviations of three independent determinations. Due to the fact that the retention time of peak 1 lay below the retention time of thiourea (log Pow is not calculable), the log Pow of this peak is stated as < 0.3. As peak 1 showed a relative area < 5 %, this peak was considered as minor peak and is not taken into account in the determination of log Pow of the test substance. Although area is not necessarily correlated to absolute concentration if a UV detector is used, it is assumed that the test substance consists mainly of peak 2. Using the correlation log K / log Pow, the log Pow of the test substance is therefore stated as 3.117 +/- 0.007 (mean i standard deviation).