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Adsorption / desorption

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Reference
Endpoint:
adsorption / desorption, other
Type of information:
experimental study
Adequacy of study:
key study
Study period:
Not specified
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 121 (Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC))
Deviations:
no
GLP compliance:
yes
Type of method:
HPLC estimation method
Media:
other: various solvents (see Details on study design)
Details on study design: HPLC method:
Test Material Characterisation - Solvent Solubility:
- A preliminary solubility evaluation was carried out by preparing the test material at a starting concentration of ~20 mg/mL by adding 5 mL of solvent (DIW, methanol, acetonitrile, chloroform, DCM, hexane) to ~100 mg of test material followed by vortex mixing. For DIW, a total of 100 mL was added. The test was repeated at a starting concentration of 1 mg/mL for THF, DCM, toluene, heptane, MTBE, and n-octanol. Final observations regarding solubility of the test material in each solvent were noted as follows:
DIW: Undissolved at 1 mg/mL
Methanol: Undissolved at 20 mg/mL
Acetonitrile: Undissolved at 20 mg/mL
Chloroform: Dissolved at 20 mg/mL
DCM: Partially soluble at 1 mg/mL
Hexane: Partially soluble at 20 mg/mL
THF: Dissolved at 1 mg/mL
Toluene: Partially soluble at 1 mg/mL
Heptane: Undissolved at 1 mg/mL
MBTE: Undissolved at 1 mg/mL
n-Octanol: Partially soluble at 1 mg/mL

Analytical Method Development Summary:
OECD 121 requires the development of an HPLC method capable of detecting the test material. To this end, a preliminary UV /vis screening was performed on a 1 mg/mL solution of the test material in chloroform. The maximum absorbance was observed at 243 nm.

- UV-Vis Absorbance Profile of the Test Material (1 mg/mL in Chloroform, 200-800 nm):
Method development continued with preliminary HPLC screening. A 1 mg/mL stock solution of the test material was prepared by dissolving ~25 mg of the test material in 25 mL of CHCl3 and a calibration curve in the range of 0.1-0.3 mg/mL was prepared by dilution of this stock. As a starting point, the screening was performed using a reverse phase Luna C18 column (100 x 3.0 mm, 5 µm) in order to establish a basic HPLC method before switching to a cyanopropyl-functionalised column as required by OECD 121 guideline. CHCl3 (100%) at 1.0 mL/min was used for the mobile phase, and 243 nm was monitored. When compared to a blank CHCl3 injection, the solutions containing the test material exhibited only a very weak, irregular signal at a low retention time.

- HPLC Chromatogram of the Test Material (0.3 mg/mL in CHCl3, Luna C18 column):
Given the low intensity and poor peak shape, it was hypothesised that this peak was not due to the test material, and that the test material had not eluted from the column. Therefore, a more polar reverse phase column (Jupiter C4, 50 x 4.6 mm, 5 µm) was used in an attempt to minimise the potential interaction between the analyte and the stationary phase. Additionally, the mobile phase was changed to 100% THF in an attempt to improve the baseline of the chromatogram. To match the new mobile phase, a ~1 mg/mL solution of the test material in CHCl3 was first prepared by dissolving ~10 mg of the test material in ~10 mL of CHCl3. A 0.1 mL aliquot of this stock was then diluted with 0.9 mL of THF to yield a 0.1 mg/mL solution for analysis. In this batch, no difference could be seen between the THF blank and the solution containing the test material.

- HPLC Chromatogram of the Test Material (0.1 mg/mL in THF, Jupiter C4 column):
Two different SEC/GPC columns (BioSep-SEC-s2000, 300 x 4.6 mm; Phenogel SOA, 300 x 7.8 mm, 5 µm) were then used in order to completely rule out interactions between the test material and reverse phase silica. Compared to the THF blank, a 0.1 mg/mL solution of the test material prepared in an identical manner to the last batch showed a small peak at ~24 min. However, when a 1.0 mg/mL solution of the test material in THF was prepared by dissolving ~10 mg of the test material directly into THF was analysed, the peak could no longer be observed. This peak was likely the result of residual CHCl3 used to prepare the 0.1 mg/mL solution of the test material in THF, as no CHCl3 was used to prepare the 1.0 mg/mL solution.

- HPLC Chromatogram of the Test Material (1.0 mg/mL in THF, Phenogel 50A column):
Lastly, to determine if the test material could be detected at all regardless of stationary phase, a solution of test material (1.0 mg/mL in THF) was injected using no column. Once more, no difference could be seen between the THF blank and the solution of the test material. This indicates that despite the test material absorbing UV light at 243 nm, under the conditions of the HPLC analysis this absorption is likely too weak to be detected.
Key result
Remarks on result:
not determinable
Remarks:
Due to the lack of an analytical method capable of detecting the test material
Details on results (HPLC method):
The test material was found to be insoluble in most common organic solvents with the exceptions of CHCl3 and THF. A preliminary UV-vis spectroscopic screening of a solution of the test material in CHCl3 showed a maximum absorbance at 243 nm. Despite this, the test material could not be detected when solutions of the test material were analysed by HPLC, regardless of the type of column. Due to the lack of an HPLC method capable of detecting the test material, the determination of the adsorption coefficient (Koc) by OECD 121 will not be possible. For this reason, a waiver from OECD 121 testing is requested.
Validity criteria fulfilled:
not applicable
Conclusions:
Due to the lack of an analytical method capable of detecting the test material, a waiver from OECD 121 testing is requested.
Executive summary:

The test material is a pale yellow solid. During preliminary evaluation of solvent solubility, the test material was found to be insoluble in water and most common organic solvents, with the exception of chloroform and tetrahydrofuran.

OECD 121 does not require an analytical method capable of quantifying the test material, but rather only requires an HPLC method capable of detecting the test material. However, despite the test material having a maximum absorbance at 243 nm, an HPLC method could not be developed as the test material could not be detected using an HPLC-UV system under a variety of conditions.

Due to the lack of an analytical method capable of detecting the test material, a waiver from OECD 121 testing is requested.

Description of key information

Due to the lack of an analytical method capable of detecting the test material, a waiver from OECD 121 testing is requested.

Key value for chemical safety assessment

Additional information

The test material is a pale yellow solid. During preliminary evaluation of solvent solubility, the test material was found to be insoluble in water and most common organic solvents, with the exception of chloroform and tetrahydrofuran.

OECD 121 does not require an analytical method capable of quantifying the test material, but rather only requires an HPLC method capable of detecting the test material. However, despite the test material having a maximum absorbance at 243 nm, an HPLC method could not be developed as the test material could not be detected using an HPLC-UV system under a variety of conditions.

Due to the lack of an analytical method capable of detecting the test material, a waiver from OECD 121 testing is requested.