Abstract: A 96-well solid phase extraction (SPE) plate assembly comprises a common base plate having plural apertures (bores), and removable extraction cartridges (containers, tubes) extending through the bores. The plate assembly is mounted on a conventional 96-well plate vacuum manifold. The cartridges preferably snap into the base plate, but may also screw in. The apertures have annular counterapertures (counterbores) complementary to annular ridges protruding from the side walls of the cartridges. Each ridge snaps into a corresponding counteraperture. The modular design allows the end user to customize the extraction medium mix of the extraction plate assembly by inserting extraction containers having different sorbents into a common base plate. Gaskets are used to maintain a vacuum seal between the base plate and extraction cartridges, for maintaining a pressure gradient across the sorbents.