(SPE). A sample-preparation technique that uses a solid-phase packing contained in a small plastic cartridge. The solid stationary phases are the same as HPLC packings; however the principle is different from HPLC. Sometimes referred to as 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. Using traditional HPLC packing materials, problems with channeling and plugging can occur. SPE columns that have been packed using PTFE to support the packing material (Empore) greatly reduce these problems.