Cartridge / column solid-phase extraction (SOPE) cartridges and discs are traditional solid-phase extraction configurations. These devices are usually in the form of a barrel of a medical syringe, packed with a small amount of sorbent. Cartridge / column solid-phase extraction devices are usually less than a gram of sorbent, although cartridges with up to 10 g are commercially available. The packing is contained in the barrel by frits, just like a high performance liquid chromatography (HPLC) column. The diameter of the packing material, usually in the 40-micron range, is larger than used in HPLC. Because efficiency is relatively unimportant in SOPE and cost is more important, irregularly shaped particle packings rather than spherical packings are used. Overall the principles of separation phase selection and method development approaches for solid phase-extraction are the same as for liquid chromatography and HPLC.