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Partition coefficient

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Endpoint:
partition coefficient
Type of information:
calculation (if not (Q)SAR)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
accepted calculation method
Justification for type of information:
Justification for using the calculation method
According to Echa guidance R7a (2017), p78:
Guidance on regulatory compliant Kow determination for surfactants:
In many cases a calculated Kow value based on the octanol and water solubilities will be the first choice for surfactants. It is also useful to compare a calculated with a measured value. For the calculation approaches, one needs to consider the pH of the system (which determines the ionisation of the surfactant – see Section R.7.1.17). None of the experimental methods is very well suited for determining the Kow of surface active substances. The shake flask method is the least suitable experimental method for surfactants. HPLC methodology may fail due to secondary interactions, and is sensitive to fluctuations of ionic strength. The slow stirring method in theory is the best, but still not demonstrated to be perfect. If using slow stirring, one needs to demonstrate a consistent result when starting with the surfactant in either phase, not just in the octanol. A working approach for surfactants might be the comparison of measured solubilities in octanol and water. However, it would then be prudent to take the critical micelle concentration in water (cmc) as a solubility limit, in order to avoid the artefact of unrealistically low Kow values.

The calculation of logKow from solubilities in water (determined via cmc) and octanol in many cases is the first choice for its derivation.


Reason / purpose:
reference to other study
Reason / purpose:
reference to other study
Qualifier:
no guideline followed
Principles of method if other than guideline:
Calculation from critical micelle concentration and solubility in octanol as described in ECHA guidance R7a (2017).
Type of method:
estimation method (solubility ratio)
Partition coefficient type:
octanol-water
Analytical method:
other: calculation from critical micelle concentration and solubility in octanol
Type:
log Pow
Partition coefficient:
>= 1.1 - <= 1.4
Remarks on result:
not measured/tested
Remarks:
calculated
Key result
Type:
log Pow
Partition coefficient:
ca. 2.4
Remarks on result:
not measured/tested
Remarks:
worst case assumption
Details on results:
For details on the calculation, please see section "any other information on results incl. tables".

Calculation

Water solubility from cmc determination:

0.02 – 0.04 % = 0.2 – 0.4 g/L

Octanol solubility:

4.8 g/L

Kow = Coctanol / Cwater

min. Kow = Coctanol / max. Cwater = 4.8 g/L / 0,4 g/L = 12;  logKow = 1.1

max. Kow = Coctanol / min. Cwater = 4.8 g/L / 0,2 g/L = 24;  logKow = 1.4

estimated calculated logKow = 1.1 – 1.4

 

Error estimation

The result of octanol solubility is reported to be not quite precise as a mixed phase was formed. Assuming a “real” octanol solubility being one order of magnitude higher (50 g/L), the following maximung logKow would result:

Maximum C(Octanol)/C(Wasser) = 50 g/L / 0,2 g/L  = 250; logKow = 2.4

worst case logKow = 2.4

Conclusions:
The estimated logKow calculated from cmc and solubility in octanol is 1.1 – 1.4. As a worst case, the logKow was calculated to be 2.4.
Executive summary:

In this calculation, the logKow of Sophorolipids: fermentation products of glucose and fatty acids, C18 (unsaturated), glycerol esters with yeast Candida, partially hydrolysed was determined. The calculation of logKow from solubilities in water (determined via cmc) and octanol in many cases is the first choice for its derivation. As Sophorolipid is a surfactant (surface tension < 40 mN/m) with acid/base active functional groups, the results from logKow determination via the HPLC method are questionable. Additional interactions between Sophorolipid charged groups and polar groups of the HPLC-column are expected that are not adequately considered by the reference compounds used at the pH of the mobile phase. This makes the result from HPLC logKow determination doubtful. Furthermore, ECHA guidance R7a (2017), p78, recommends to take the critical micelle concentration in water (cmc) as a solubility limit, in order to avoid the artefact of unrealistically low Kow values. The calculations lead to the following values:

Estimated calculated logKow = 1.1 – 1.4.

Worst case logKow = 2.4.

Endpoint:
partition coefficient
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
2015-03-05 to 2015-03-19
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 117 (Partition Coefficient (n-octanol / water), HPLC Method)
Version / remarks:
adopted on 13 April 2004
Deviations:
no
Qualifier:
according to
Guideline:
EU Method A.8 (Partition Coefficient)
Version / remarks:
30 May 2008
Deviations:
no
GLP compliance:
yes (incl. certificate)
Type of method:
HPLC method
Partition coefficient type:
octanol-water
Analytical method:
high-performance liquid chromatography
Type:
Pow
Partition coefficient:
34.754
Temp.:
25 °C
pH:
3
Remarks on result:
other: pH of mobile phase
Key result
Type:
log Pow
Partition coefficient:
4.5
Temp.:
25 °C
pH:
3
Remarks on result:
other: pH of mobile phase
Details on results:
See section "any other information on results incl. tables".

Results of the HPLC measurements of the standard reference items used for calibration

 

Sample

tR1

[min]

tR2

[min]

tR

[min]

k

log k(x)

log POW(y)

Urea (inert marker)

0.82

0.83

0.83

---

---

---

Cinnamyl alcohol

1.24

1.24

1.24

0.494

-0.306

1.91)

Trans-cinnamic acid

1.23

1.23

1.23

0.482

-0.317

2.11)

Ethyl benzoate

1.75

1.76

1.76

1.120

0.049

2.61)

Phenyl benzoate

2.24

2.24

2.24

1.699

0.230

3.61)

Dibutyl phthalate

4.19

4.19

4.19

4.048

0.607

4.12)

Dodecanoic acid

7.66

7.66

7.66

8.229

0.915

4.21)

Bis(2-ethylhexyl) phthalate

57.02

56.97

57.00

67.675

1.830

7.93)

 

tR= retention time (tR1and tR2= double determinations; tR= mean value)

k = capacity factor

1) Results from the OECD guideline for the testing of chemicals No. 117: „Partition Coefficient (n-octanol/water), HPLC method“ (13 April 2004).

2) Results from M. Harnisch et al., J. Chromatogr. 282, 315-333 (1983)

3) Results from W. Klein et al., Chemosphere, Vol. 17 No. 2, 361-386 (1988)

4) Interpolated from linearized function log POW=  f(log k’ ) of the calibration data.

Results of the HPLC measurements of the additional reference items and of the test item

 

Test item compound no.

tR1

[min]

tR2

[min]

k

log k

log POWafter

interpolation1) 

log POW

mean value

area %

mean value

1

2.24

 

1.699

0.230

3.251

n. u.

1.19355

 

2.25

1.711

0.233

3.259

2

2.48

 

1.988

0.298

3.428

n. u.

2.8067

 

2.49

2.000

0.301

3.436

3

2.94

 

2.542

0.405

3.707

3.707

14.6899

 

2.94

2.542

0.405

3.707

4

3.52

 

3.241

0.511

3.983

3.9845

14.01415

 

3.53

3.253

0.512

3.986

5

4.21

 

4.072

0.610

4.241

4.241

12.40785

 

4.21

4.072

0.610

4.241

6

4.73

 

4.699

0.672

4.403

4.403

2.0781

 

4.73

4.699

0.672

4.403

7

5.25

 

5.325

0.726

4.544

4.544

21.4888

 

5.25

5.325

0.726

4.544

8

6.69

 

7.060

0.849

4.864

4.864

4.2905

 

6.69

7.060

0.849

4.864

9

7.26

 

7.747

0.889

4.969

4.969

6.5457

 

7.26

7.747

0.889

4.969

10

8.31

 

9.012

0.955

5.141

5.141

6.71125

 

8.32

9.024

0.955

5.141

11

9.51

 

10.458

1.019

5.307

5.307

6.773

 

9.50

10.446

1.019

5.307

12

11.17

 

12.458

1.095

5.506

5.506

11.0008

 

11.17

12.458

1.095

5.506

13

12.11

 

13.590

1.133

5.605

n. u.

0.8888

 

12.08

13.554

1.132

5.602

Sophorolipid-Acid reference standard

2.97

 

2.578

0.411

3.723

3.723

----

 

2.97

2.578

0.411

3.723

----

Sophorolipid-Lactone reference standard

11.20

 

12.494

1.097

5.511

5.511

----

 

11.19

12.482

1.096

5.508

----

 

1) Interpolated from linearized function log POW=  f(log k) of the calibration data.

tR= retention time

k = capacity factor

n. u. = not used for test evaluation

 

For the test evaluation only the log Pow mean values in the range between the Sophorolipid-Acid reference standard and the Sophorolipid-Lactone reference standard were used. This range covers 95.1 % of the total compounds of the test item.

Based on these data the weighted average log Pow was calculated 4.541. Weighted average log Pow= 4.541

Conclusions:
Partition coefficient n-octanol / water (POW) at 25 °C (weighted average): POW = 34.754 / log POW = 4.5
Executive summary:

The partition coefficient n-octanol / water (KOW) of the substance was determined according to OECD guideline no. 117 [adopted on 13 April 2004] and EU test method A.8 [Council Regulation (EC) No 440/2008 of 30 May 2008] with the HPLC method.

Partition coefficient n-octanol / water (POW) at 25 °C (weighted average): POW= 34.754 /  log POW= 4.5

Description of key information

Calculated from cmc and solubility in n-octanol as a worst case assumption.

Key value for chemical safety assessment

Log Kow (Log Pow):
2.4

Additional information

In this calculation, the logKow of Sophorolipids: fermentation products of glucose and fatty acids, C18 (unsaturated), glycerol esters with yeast Candida, partially hydrolysed was determined. The calculation of logKow from solubilities in water (determined via cmc) and octanol in many cases is the first choice for its derivation. As Sophorolipid is a surfactant (surface tension < 40 mN/m) with acid/base active functional groups, the results from logKow determination via the HPLC method are questionable. Additional interactions between Sophorolipid charged groups and polar groups of the HPLC-column are expected that are not adequately considered by the reference compounds used at the pH of the mobile phase. This makes the result from HPLC logKow determination doubtful. Furthermore, ECHA guidanceR7a (2017), p78,recommends to take the critical micelle concentration in water (cmc) as a solubility limit, in order to avoid the artefact of unrealistically low Kow values. The calculations lead to the following values:

Estimated calculated logKow = 1.1 – 1.4.

Worst case logKow = 2.4.