• While the solvent extraction uses two immiscible phases (water
and an organic solvent), the solid-phase extraction uses a solid
chromatographic packing and liquid sample. This provides a
more rapid separation method.
• The chromatographic packing may be any of a number of
different materials (e.g., ion-exchange resins or a reversed- or
normal-phase HPLC column packing).
• When a sample is passed through the cartridge or filter, solutes
that have an affinity for the chromatographic phase will be
retained on the phase while those with little or no affinity will
pass through.
• The phase is then rinsed with water, or a weak solvent if a
reversed-phase technique is used, and then a stronger solvent.
The strong eluent is chosen such that it will remove the solutes
of interest.