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Solubility in organic solvents / fat solubility

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Reference
Endpoint:
solubility in organic solvents / fat solubility
Type of information:
experimental study
Adequacy of study:
key study
Study period:
June 27, 2017 - December 11, 2017
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
comparable to guideline study
Qualifier:
equivalent or similar to
Guideline:
other: OECD Guideline 105
Version / remarks:
Solubility measured in n-octanol instead of water
GLP compliance:
yes (incl. certificate)
Specific details on test material used for the study:
- Analytical purity: 100% (UVCB)
- Purity test date: 06 June 2017
- Lot/batch No.: 180517GT41
- Expiration date of the lot/batch: 31 December 2017
- Appearance: Beige pasty solid
- Storage: At room temperature
Key result
Medium:
n-octanol
Solubility:
276 mg/L
Temp.:
20 °C

RESULTS

Preliminary test

Preliminary test – 10 g/L. Based on the response for C18:1 amido propyl betaine, the content of test item dissolved in the n-octanol sample was 11.4 g/L after 3 centrifugation steps and 10.8 g/L after 4

centrifugation steps.

Preliminary test – 100 g/L. Based on the response for C18:1 amido propyl betaine, the content of test item dissolved in the n-octanol sample was 118 g/L after 3 centrifugation steps and 117 g/L after 4

centrifugation steps

Main study

Both mixtures prepared during the preliminary test were turbid (suspensions). After centrifugation for 5 minutes at 61421 g, undissolved material was observed at the bottom of the centrifugation tube. As test item concentrations based on the response for C18:1 amido propyl betaine were the nominal concentrations, it was concluded that the C18:1 form had completely dissolved but another form not. For the measurement of n-octanol solubility of all compounds in the test item, an approach similar to that of critical micelle concentration was used, turbidity being measured instead of surface tension. By extrapolation to zero turbidity, the concentration at which all compounds of the test item have dissolved is obtained. Standard techniques of linear regression were applied to estimate the concentration at zero turbidity i.e. the value which represents the n-octanol solubility.

The results of the test on the determination of the turbidity for the test samples are given in the table below.

Nominal concentrations

[mg/L] 

Turbidity

[NTU] 

Corrected turbidity*

[NTU] 

0

0

103

103

204

204

418

418

804

804

1060

1060

1190

1190

1598

1598

1986

1986

4030

4030

5972

5972

7922

7922

0.096

0.080

1.02

0.698

0.875

1.13

3.39

2.61

8.96

8.14

10.1

9.95

 

13.5

13.9

18.8

18.2

23.8

24.4

44.5

44.2

89.4

85.1

118

117

n.a.

n.a.

0.932

0.610

0.787

1.04

3.30

2.52

8.87

8.05

10.1

9.86

13.4

13.8

18.7

18.1

23.7

24.3

44.4

44.1

89.3

85.0

118

117 

*Corrected for the mean turbidity of the blank samples

Since a response was observed in blank n-octanol, it was decided to correct for the mean turbidity of the blank samples. The samples at test item concentrations of 103 and 204 mg/L had a similar response. Therefore, these results were considered as background and omitted from the curve. Samples at a test item concentration of 4030, 5972 and 7922 mg/L were also omitted from the curve because using them resulted in a negative n-octanol solubility (not reported in detail). In the concentration range of 418 to 1986 mg/L, a linear relationship between response and test item concentration was observed. The equation of the regression line was:

Y = 0.0134 x A – 2.858 (r = 0.994, n = 12), where Y is the turbidity measured in NTU and A is the nominal concentration of the test item.

Since turbidity at 103 and 204 mg/L was similar, the mean response was calculated to be 0.843 NTU. This value was substituted in the regression line to obtain the concentration at which turbidity increases as a result of the addition of test item. This concentration is considered as the n-octanol solubility. It was 276 mg/L.

Conclusions:
The n-octanol solubility of the test item at 20.0 ± 0.2°C was estimated to be 276 mg/L.
Executive summary:

The n-octanol solubility of the test item was determined in a GLP-compliant study performed in accordance with a method equivalent or similar to OECD Guideline No. 105. (solubility measured in n-octanol instead of water). The n-octanol solubility of the test item at 20.0 ± 0.2°C was estimated to be 276 mg/L.

Description of key information

The n-octanol solubility of the test item was determined in a GLP-compliant study performed in accordance with a method equivalent or similar to OECD Guideline No. 105. (solubility measured in n-octanol instead of water). The n-octanol solubility of the test item at 20.0 ± 0.2°C was estimated to be 276 mg/L.

Key value for chemical safety assessment

Solubility in organic solvents at 20°C:
276 mg/L

Additional information

The n-octanol solubility of the test item was determined in a GLP-compliant study performed in accordance with standard methods, without deviations. The study is considered as reliable (Klimisch 1) and is selected as a key study for the endpoint.