Solvent desorption pipette is commonly used for air sampling in industrial hygiene environments. It is a sealed glass tube filled with adsorbent, usually consisting of two layers. Layer A is a packed bed with one more layer, while layer B is a packed bed with one less layer (as shown in the figure below). Less layer of packed bed is used as a backup filling material to capture compounds that penetrate due to the overload of the previous layer of packed bed. The packed beds are generally separated by quartz wool or foam and fixed in glass tubes.