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For capillary columns, polysiloxanes (also known as silicone oils and gums) are the mostly commonly used stationary phases. They are based upon a repetitive backbone that consists of two hydrocarbon chains per silicon atom (Figure 2.8). Dozens of different compositions of alkyl or aryl chains (methyl or phenyl), onto which can be incorporated further functional groups (e.g. cyanopropyl, trifluropropyl), are available on the market. Monomers combined in various proportions also convey changes in the properties of stationary phases (polarity, stability range). As such, dimethylpolysiloxanes have a very large temperature range, from −50 to 300/325°C.