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These columns, less commonly used today, have diameters of 1/8 or 1/4 inch (3.18 or 6.35 mm) and a length of 1–3 m. Manufactured from steel, the internal wall of the tube is treated to avoid catalytic effects with the sample. The carrier gas flow rate ranges from 10 to 40 ml/min.

 In gas–liquid chromatography, the column contains an inert porous support onto which the stationary phase can be impregnated or grafted (between 3 and 25%), depending on the expected application.

 In gas–solid chromatography, the stationary phase is composed of an adsorbent solid (molecular sieve, glassy carbon or porous polymer).

Figure 2.7 Capillary columns. Representation of a 50 m long commercial capillary column coiled around its metal support (Document from the Alltech Associates Inc.) and close‐up of a column. At this scale, the thickness of the stationary phase will scarcely be visible.

While less efficient than capillary columns, owing to preferential paths (Eddy factor of the Van Deemter curve), they are still used for some standardized routine analyses. Nevertheless, these are not adapted to trace analyses, and the progressive generalization of GC‐MS coupling has greatly reduced their use.

Porous supports are made of spherical particles of around 0.2 mm in diameter. These are obtained from fossilized silicates (kieselguhr, tripoli) whose backbone is chemically comparable to that of amorphous silica. One of the most common goes by the name of Chromosorb^®. Their specific surface area is variable (between 2 and 8 m² /g).