Chemistry: Extraction

Extraction

• Extraction is the transference of a solute from one phase to another phase.
• It can involve different physical phases of the same substance (e.g., liquid water and water vapor) or the same physical phases of different substances (e.g., liquid water and liquid hexane).

Goals of Extraction

• Concentration: transferring an analyte from the original solvent to a smaller volume of a new solvent, resulting in substantial enrichment and concentration of analytes.
• Isolation: separating individual compounds from a complex matrix or isolating a solute from a reaction solvent that is difficult to remove by evaporation.

Types of Extraction

Solid-Liquid Extraction (SLE)

• Also known as leaching, it involves the transfer of a solute from a solid phase to a liquid phase.
• Examples of SLE include extracting color and flavor from tea leaves, fixed oil from seeds, etc.
• Factors affecting the rate of leaching:
  • Particle size: smaller particles increase the leaching rate due to greater interfacial area and shorter diffusing pathway.
  • Solvent nature: selectivity and low viscosity are important for easy circulation.
  • Temperature: increased solubility of extractable material with temperature facilitates its escape from the matrix.
  • Agitation: increases eddy diffusion and material transfer from particle surface to bulk solution.
  • Extraction duration: longer extraction time increases leeching rate.
  • Extraction times: repeating extraction multiple times enhances extraction rate.

Solid-Liquid Extraction Process

• The extraction of natural products from solid resources progresses through:
  • Solvent penetration into the solid matrix.
  • Solute dissolution in the solvent.
  • Solute diffusion out of the solid matrix.
  • Collection of extracted solutes.

Solid Phase Extraction (SPE)

• Transfer of a solute from a continuously streaming liquid (mobile phase) to a fixed solid beads (stationary phase) mainly packed in a column.
• One or more analytes from a liquid sample are isolated by extracting, partitioning, and/or adsorbing onto the solid stationary phase.
• Solutes are separated based on their different adsorption affinities towards the adsorbent surface.

SPE Steps

• Conditioning: activating the adsorbent surface to promote analyte interaction or removing impurities.
• Sample loading: passing the sample solution through the column packed with adsorbent.
• Washing: removing impurities and interfering compounds.
• Elution: desorbing the analyte from the adsorbent surface.