Open tubular column:

The other type of column is the open tubular column. This is common 0.25 mm ID tubing. A liquid phase is coated straightly on the inside wall of the tubing; thus, no additional packing is required. Because of small surface areas included and the resulting limited capacity for solutes, these columns are of necessity long (20 to 50 m) and need the use of a specialized sample inlet. Because capillary columns are not filled along with particles, band broadening because of eddy diffusion does not exist. The design of an open tubular column is display in Figure.

Figure:  Open tubular column

A comparison of packed and capillary columns provided in Table displays some interesting differences. A main advantage of capillary columns is the total plates obtainable. Plates per metre of column length are comparable along with packed columns but much longer columns are usable since capillary columns have high permeabilities, that is. they are "open tubes" along with small resistance.