Liquid–liquid extraction separates compounds according to how they distribute between two liquids that do not mix, such as water and an organic solvent. This lesson introduces the physical basis of extraction and the measurements used to describe its effectiveness.
When two immiscible liquids are brought into contact, a solute can transfer from one phase to the other. The solute tends to dissolve more readily in the liquid with which it has greater chemical affinity. In a common example, polar compounds favor a polar aqueous phase, while less-polar compounds may favor a nonpolar organic phase.
All flashcards
What is liquid–liquid extraction?
A separation method in which a solute transfers between two immiscible liquids according to its relative affinity for each phase.
What are the extract and raffinate?
The extract is the phase enriched in transferred target solute; the raffinate is the phase remaining after extraction.
How does D differ from Kd?
D compares total solute concentrations in the phases under specified conditions. Kd describes equilibrium partitioning of a particular chemical form.
What does a separation factor measure?
The ratio of two solutes’ distribution ratios, indicating relative extraction selectivity.
What is dispersive liquid–liquid microextraction (dLLME)?
An extraction method that disperses a small amount of solvent into fine droplets, then uses centrifugation to separate phases.
Quiz questions
Silver has a distribution ratio of 100 and nickel has a distribution ratio of 10. What is the silver-to-nickel separation factor?Answer: 10
What distinguishes a mixer–settler from a centrifugal extractor?Answer: It uses separate zones for mixing and gravity settling.
In solvation extraction, what promotes transfer of a solute into the organic phase?Answer: An extractant associates with the solute to form an organic-soluble complex.
What is the purpose of the dispersive solvent in dLLME?Answer: It helps disperse the extraction solvent into many small droplets.
How do amines commonly partition under acidic conditions during liquid–liquid extraction?Answer: They become protonated and often favor the aqueous phase.