Column:

The unpacked column must be constructed of materials that will withstand both the pressures to be used and chemical action of the mobile phase. Most columns are made up of stainless steel tubing. However, heavy wall glass columns are sometimes used. Columns which will withstand pressures up to 600 psi are commercially available. For operation at high pressures, glass lined metal columns also could be used. The column end fittings should be designed along with minimum dead volume. A Porous plugs are used in the ends of columns to retain the packing. Straight sections of liquid chromatography columns in lengths of 25-150 cm are generally preferred. A few columns might also be bent into a "U" shape.  Coiled columns are sometimes used, but are often less efficient than columns prepared in straight sections. Precolumns commonly are desirable. The precolumn ensures in which the mobile phase is completely saturated with the stationary phase before it passes in to the carefully prepared analytical column. The internal diameter of the column has a significant effect on the efficiency of liquid chromatography columns. For analytical studies, columns 1-4 mm internal diameter (i.d.) are normally used. Columns of larger internal diameter are used for preparative work.