Microliter scale solid phase extraction devices for preparing analytes in microliter volumes are disclosed. A re-useable device is provided in cartridge form that includes a central containment member with a containment bore that holds as little as 1 to 5 .mu.l or less of a solid phase material that binds the analyte. The containment bore is enclosed on either side by a porous membrane that has an inner portion exposed for fluid flow and a peripheral portion that is sealed against fluid flow. The seal is formed by engaging the periphery of the porous membranes between sealing surfaces of the central containment member and corresponding sealing surfaces on first and second conduit assemblies that comprise the remainder of the cartridge. A non-reuseable device is provided in "chip" form, which includes a porous filter sandwiched between top and bottom wafers each having a plurality corresponding input and output conduits for a plurality of samples.
STATEMENT REGARDING RESEARCH & DEVELOPMENT
 This invention was made with Government support under government contract no. DE-AC04-94AL85000 awarded by the U.S. Department of Energy to Sandia Corporation. The Government has certain rights in the invention, including a paid-up license and the right, in limited circumstances, to require the owner of any patent issuing in this invention to license others on reasonable terms.