OECD 105: Analysis of Chemical Substances by Determination of Solubility in Water

OECD 105: Determination of Water Solubility

What is Water Solubility?

It can be defined as the capacity of a substance to dissolve in a certain amount of water at a certain temperature and to form a homogeneous solution. Water solubility of substances is important for understanding their environmental behavior and bioavailability.

What are the Factors Affecting Water Solubility?

• Temperature: An increase in temperature generally increases solubility. However, for some substances solubility may decrease with temperature.
• pH: The solubility of the substance may vary depending on the pH value.
• Purity of Solvent: The purity of the water used (distilled or deionized water) is one of the factors affecting solubility.

Application Areas of Water Solubility Determination

• Environmental Sciences: Solubility information is analyzed to determine how a chemical diffuses into aquatic ecosystems and its environmental risks.
• Pharmaceutics: Bioavailability and efficacy of drugs are affected by the solubility of the drug.
• Industry: In chemical processes, the solubility of the substance is an important point in production and formulation processes.

Analytical Methods Used in Water Solubility Determination

• High Performance Liquid Chromatography (HPLC)
• Gas Chromatography (GC)
• UV/Visible Spectrophotometry
• Mass Spectrometry (MS)

What is the Scope of “OECD 105: Determination of Water Solubility”?

The solubility of chemicals in water can be greatly affected by the presence of impurities. The OECD 105: Water Solubility guide includes the test method for determining the solubility in water of pure substances that are stable and non-volatile in water. Within the scope of the guideline, the test methods for substances with solubility below or above 102 g/l are respectively as follows:

Shake Flask Method:

• Solubility is achieved by shaking a certain amount of substance with a certain volume of water.
• The solution is filtered and the amount of dissolved substance is determined.

Column Elution Method:

• The substance is eluted with water in a column filled with a solid support material.
• The eluate is analyzed to determine the amount of dissolved substance.

OECD 105: Determination of Water Solubility is suitable for substances with a water solubility below 0.1 mg/L. Since solubility is temperature dependent, solubility tests should be performed at a constant temperature, typically 20°C or 25°C. Deionized or distilled water should be used in the analysis process to avoid interference from impurities. To obtain accurate solubility values, ensure that the solution has reached equilibrium before sampling.

It may also be necessary to know the properties of the sample to be tested, such as structural formula, vapor pressure, dissociation constant and pH, before testing. It includes a simple preliminary test to determine the approximate appropriate amount of the sample as well as the time required to reach saturation before the final test at 20 ± 0.5 °C.

OECD 105: Water Solubility

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