A technique for sample preparation using a 20–40 μm dp solid-phase packing contained in a small plastic cartridge, disk, or in the wells of a 96-well flowthrough plate. The solid stationary phases used are identical to HPLC packings. Although related to chromatography, the principle of SPE is different and is sometimes called digital chromatography. The process as most often practiced requires four steps: conditioning the sorbent, adding the sample, washing away the impurities, and eluting the sample in as small a volume as possible with a strong solvent.