The Basics of Solvent Drying

Solvent drying is a key step in many laboratories that are using organic solvents for syntheses and extractions. In the case of hexane extractions during oil and grease measurements, this step is necessary to ensure that the extracts are accurately dried, concentrated and weighed.

Given the importance of solvent drying during the extraction of hexane extractable materials (HEM), I wanted to clarify any confusion around its definition in this 2-part blog series. In the first part, I will outline the difference between solvent drying and solvent evaporation. The second part will focus on options for performing solvent drying following an n-hexane extraction.

Solvent drying involves the use of a drying agent to remove excess water from an organic solvent. This is different from solvent evaporation which is a process that reduces the solvent volume through vaporization. The volume reduction involves a phase change, not a chemical change, as the solvent converts from a liquid to a gas.

Solvents are typically dried using a drying agent, such as sodium sulfate. When added to the solvent, a drying agent absorbs any water present, forming a hydrated salt, which can then be filtered out and removed from the now “dry” solvent. This is not to be confused with the use of a dehydrating agent which reacts with water in the solvent. Specifically, these compounds react with the hydrogen and oxygen (2 hydrogen atoms and 1 oxygen atom to be exact!) in the solvent to generate a reaction and produce a physical and/or chemical change.

So, to recap, solvent drying is important in performing oil and grease measurements to remove water from the hexane extraction layer. If left in the solvent, the excess water will hinder the subsequent solvent evaporation, and affect the weight of the final (dried) extracts.

Stay tuned for the second part in the series. If you have any additional terms you would like clarified, feel free to add them to the comments section.

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