In liquid-solid extraction, a solvent (hydrophilic or hydrophobic, acidic, neutral or basic) is added to a solid. Insoluble material can be separated by gravity or vacuum filtration, and soluble material is 'extracted' into the solvent. A sequence of solvents, of varying polarity or pH, can be used to separate complex mixtures into groups. The filtered solution can be used as a solution (for example, to be injected into the GC/MS system) or the solvent can be evaporated to recover the solute(s) in powder or crystalline form.
The figures below show several simple liquid-solid extraction schemes. {insert figures}