Extraction and separation of chemical species

  • Knowledge and skills
  • Understand the principle of solvent extraction and hydrodistillation
  • Learn how to use a data table to choose a solvent or develop an experimental protocol
  • Learn about the risks and safety instructions to be followed when using organic solvents

I - Introduction:

When making tea, it is the taste and aroma contained within the leaves that are sought after. To obtain a good tea, it is necessary to transfer these substances from the leaves to the water (as they are soluble in water). A scientist would describe this process as the extraction of colorants and aroma from the tea using a solvent (water). Various techniques are available for this purpose. What are they? And how are they performed?

Guide to Brewing Tea

II - Liquid-liquid extraction:

Process

  1. Water (the initial solvent) and the chemical species to be extracted are placed in a separating funnel (aqueous phase).
  2. The extracting solvent is added (organic phase).
  3. The separating funnel is closed, agitated to mix the contents, and then opened to release any gas.
  4. The separating funnel is set aside, allowing the two phases to separate through decantation:
  • The organic phase contains the extracting solvent and the extracted chemical species (The chemical species is more soluble in the extracting solvent than the initial one).
  • The aqueous phase contains the initial solvent.The denser phase settles at the bottom of the separating funnel, while the less dense phase rises to the top
  1. Both solutions are carefully collected in separate beakers.

III- Solid-liquid extraction:

Step 1 - Direct solvent extraction

Direct solvent extraction involves dissolving a solid by allowing it to pass into a liquid, either through maceration, decoction, or infusion:

  • Maceration: This operation entails soaking a substance in an open vessel filled with a liquid to extract soluble components. Example: pickles
Le jus de cornichons : allié minceur et digestion | gourmandiz.be
  • Infusion: It’s a method of extracting active compounds or aromas from a plant by dissolving them in an initially boiling liquid.
  • Decoction: This method extracts active compounds and/or aromas from typically harder plant parts (e.g., roots, seeds, bark, wood) by dissolving them in boiling water.
Infusion, décoction, macération, quelle différence ?

Step 2 - Filtration

One can use a simple filter to separate solids from liquids.

Note : Regular filtration takes time. In laboratories, chemists and biologists tend to use a more complex yet fast type of filtration: the vacuum filtration (Büchner filtration)

IV- Hydrodistillation:

Step 1 - Extraction of essential oil:

This involves the distillation of a mixture of water and a natural product placed in a flask.

When heating this mixture, the aromas from the natural product are carried away by the steam. To recover these aromas, the vapors are condensed using a cooler (refrigerant/condenser), allowing the recovery of the aromas. The distillate obtained in the test tube consists of two phases: an organic phase containing the essential oil and an aqueous phase containing water.

Step 2 - Liquid-liquid extraction:

A liquid-liquid extraction process is carried out to recover the essential oil using a separating funnel.