Guard column:

In order to increase the life of analytical column, a short guard column, also called precolumn, is placed before the major column as display in Figure. It removes contamination from the solvent. Guard column serves to saturate the mobile phase with the stationary phase so that losses of stationary phase in the column are minimized. Therefore, it is necessary in which the composition of the guard column should be similar to that of the analytical column but its particle size may be larger to minimize the pressure drop.