The photo below shows a typical example of a packed column for gas chromatography. This column is made from stainless steel and is 2 m long with an internal diameter of 3.2 mm. The packing material in this column has a particle diameter of 149–177 μm. To put this in perspective, beach sand has a typical diameter of 700 μm and the diameter of fine grained sand is 250 μm.
Shown here is a typical example of a capillary column for gas chromatography. This column is 30 m long with an internal diameter of 247 μm. The interior surface of the capillary has a 0.25 μm coating of the liquid phase.
There are three common types of capillary columns, which differ in how the stationary phase and/or solid support are coated into the column. Shown below are cross-sections through these columns. WCOT: wall-coated open tubular column; PLOT: porous-layer open tubular column; SCOT: support-coated open tubular column