Solid phase extraction tubes are used for sample preparation. The sorbent extraction process involves physical extraction of a dissolved analyte into or onto a selective sorbent solid phase. As the target analyte sorbs onto the material, the remaining matrix does not sorb, and elutes through the column bed thus concentrating the analyte onto the material. The analyte is subsequently eluted with a strong solvent. SPE tubes come in a variety of volumes and can have one or more distinct layers or mixtures of sorbents.