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Physical & Chemical properties

Partition coefficient

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Endpoint:
partition coefficient
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Principles of method if other than guideline:
The partition coefficient was defined as the ratio of the total concentration of the solute (glycolic acid) in the alcoholic phase (n-octyl alcohol) to its total concentration in the aqueous phase.
GLP compliance:
not specified
Partition coefficient type:
octanol-water
Analytical method:
not specified
Type:
log Pow
Partition coefficient:
-1.11
Temp.:
19 °C
Conclusions:
The partition coefficient of glycolic acid in octyl alcohols was 0.077 (Pow) (logPow -1.1) and in oleyl alcohols was 0.02.
Executive summary:

The partition coefficient of glycolic acid in octyl alcohols was 0.077 (Pow) (logPow -1.1) and in oleyl alcohols was 0.02.

Endpoint:
partition coefficient
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Remarks:
Test substance details are unavailable within the report.
Qualifier:
according to guideline
Guideline:
OECD Guideline 117 (Partition Coefficient (n-octanol / water), HPLC Method)
Deviations:
not specified
GLP compliance:
yes
Type of method:
HPLC method
Partition coefficient type:
octanol-water
Analytical method:
high-performance liquid chromatography
Type:
log Pow
Partition coefficient:
< 0
Temp.:
20 °C
pH:
4

The test substance was completely soluble in methanol:water 3:1 and gave clear solution at a concentration of 1.2 mg.ml-1. A peak with retention time of ca. 2 min was a system peak.

Conclusions:
A partition coefficient test (n-octanol/water; OECD 117) was performed on glycolic acid 70% solution. The log Pow was < 0.
Executive summary:

A partition coefficient test (n-octanol/water; OECD 117) was performed on glycolic acid 70% solution. The log Pow was < 0.

Endpoint:
partition coefficient
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Reason / purpose for cross-reference:
reference to same study
Qualifier:
according to guideline
Guideline:
OECD Guideline 117 (Partition Coefficient (n-octanol / water), HPLC Method)
Deviations:
no
Qualifier:
according to guideline
Guideline:
EPA OPPTS 830.7550 (Partition Coefficient, n-octanol / H2O, Shake Flask Method)
Deviations:
no
GLP compliance:
yes
Type of method:
HPLC method
Partition coefficient type:
octanol-water
Analytical method:
high-performance liquid chromatography
Type:
log Pow
Partition coefficient:
< 0.3
Temp.:
25 °C
pH:
4
Type:
log Pow
Partition coefficient:
< 0.3
Temp.:
25 °C
pH:
7
Type:
log Pow
Partition coefficient:
< 0.3
Temp.:
25 °C
pH:
10
Details on results:
For each pH value, a mean exponential regression of the known partition coefficients of the standards versus their capacity factors was prepared, from which the partition coefficient of glycolic acid >99% was calculated.
Conclusions:
The partition coefficient of glycolic acid >99% was found to be less than 2 (log Pow < 0.3) at pH 4, 7 and 10.
Executive summary:

The partition coefficient of glycolic acid >99% was found to be less than 2 (log Pow < 0.3) at pH 4, 7 and 10.

Endpoint:
partition coefficient
Type of information:
experimental study
Adequacy of study:
key study
Study period:
13 January 2021 - 18 August 2021
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Qualifier:
according to guideline
Guideline:
EU Method A.8 (Partition Coefficient - Shake Flask Method)
Qualifier:
according to guideline
Guideline:
OECD Guideline 107 (Partition Coefficient (n-octanol / water), Shake Flask Method)
Deviations:
yes
Remarks:
see details on results below
GLP compliance:
yes (incl. QA statement)
Type of method:
flask method
Partition coefficient type:
octanol-water
Key result
Type:
log Pow
Partition coefficient:
< -1.52
Temp.:
20 °C
pH:
2
Key result
Type:
log Pow
Partition coefficient:
< -1.22
Temp.:
20 °C
pH:
5
Key result
Type:
log Pow
Partition coefficient:
< -1.2
Temp.:
20 °C
pH:
7
Key result
Type:
log Pow
Partition coefficient:
< -1.25
Temp.:
20 °C
pH:
9
Details on results:
Due to issues with the method validation, for the partition coefficient, the validation results were not acceptable. It was felt that this was probably due to interferences due to the use of the pH buffers which resulted in changed chromatography for the method. Based on this it was concluded that the analytical method used was not suitable for analysis in buffers.

These issues with the analytical method meant that it was considered that definitive results for partition coefficient could not be obtained with this method. In addition the partition coefficient testing that was carried out gave some concentrations in the aqueous phases which were above the maximum specified concentration of 0.01M which meant results would not be acceptable.
Based on these issues with the analytical method it was decided that the partition coefficient would be estimated based on solubilities of the test item in aqueous buffers and in n-octanol.

The solubilities in aqueous buffers for the pH 5, 7 and 9 buffers were taken from the water solubility results. The solubilities in the pH 2 buffer and n-octanol were taken from the solubility assessments based on visual observation.
Conclusions:
The log Pow of the test substance was found to be < -1.20 at 20 °C and pH 7.This is a calculated value using aqueous solubility by sample analysis and octanol solubility by visual assessment. Effect of pH was assessed at pH 2, 5, 7 and 9 and results demonstrated that pH has minimal effect on the partition coefficient.

Description of key information

The partition coefficient (logKow) of glycolic acid was determined to be < -1,2 at pH 2, 5, 7 and 9.

Key value for chemical safety assessment

Log Kow (Log Pow):
-1.2
at the temperature of:
20 °C

Additional information

Four experimental data are available, providing values in agreement:


- logPow between < -1,52 and < -1,2 at pH 2, 5, 7 and 9 (K2; ratio of solubilities; Foster 2021),


- log Pow < 0.3 (S1; HPLC; HLS 2002),


- logPow < 0 (S2; HPLC; Terra Env 1998),


- log Pow = -1.11 (S2; ratio of solubilities; literature, Collander 1951).


In the Foster study, an attempt was made to determine logKow with the flask method, but due to issues with the analytical method validation, the results were estimated from the ratio of solubilities in each media. It is nevertheless considered reliable, and of higher interest than HPLC results, based on lower limit value. Therefore it was chosen as the key study. The higher value of the range is retained as key value, as the worst-case to cover the whole pH scale.