Solid-phase extraction (SPE) is an extraction method that uses a solid phase and a liquid phase to isolate one, or one type, of analyte from a solution. It is usually used to clean up a sample before using a chromatographic or other analytical method to quantitate the amount of analyte(s) in the sample.
The general procedure is to load a solution onto the SPE phase, wash away undesired components, and then wash off the desired analytes with another solvent into a collection tube.
Solid-phase extractions use the same type of stationary phases as are used in liquid chromatography columns. The stationary phase is contained in a glass or plastic column above a frit or glass wool. The column might have a frit on top of the stationary phase and might also have a stopcock to control the flow of solvent through the column. Commercial SPE cartridges have 1-10 mL capacities and are discarded after use. The picture below shows a 3 mL cartridge on a vacuum manifold, which increases the solvent flow rate through the cartridge. A collection tube is placed beneath the SPE cartridge (inside the vacuum manifold for the example in the picture) to collect the liquid that passes through the column.
Illustration of a solid-phase extraction set-up