Gas Chromatography - GC Columns > Column Packing > Page 24
In the slurry method of coating, a weighed amount of the support is placed in the flask of a rotary evaporator and the required mass of stationary phase added. An appropriate volatile solvent is then added in sufficient quantity to produce a free flowing slurry. The flask is then rotated at room temperature for ten minutes to ensure complete mixing. The rotating flask is then heated and the solvent removed by evaporation. When the packing appears dry, the material is then heated to about 150˚C in and oven to remove the final traces of solvent. This method of coating gives an extremely homogeneous surface distribution of stationary phase throughout the support and an accurate value for the stationary phase loading.
Short columns are usually straight and can be packed vertically. The packing is added, about 0.5 ml at a time, and the column tapped until the packing had settled. Another portion of packing is then added and the process repeated until the column is full. U-shaped columns are packed in the same manner. Columns up to 50 ft long can be packed in a series of U's and then each U column joined with a low dead volume connection. If the columns were glass they were usually filled through an opening at the top of each U which was terminated in a plug of quartz wool and sealed-off in a blow-pipe flame. These long packed columns could be operated at a maximum of 200 psi. and could provide efficiencies of up to 50,00 theoretical plates. Such columns could tolerate charges of several microliters. A chromatogram of the isomeric heptanes and octanes obtained from a 50 ft column is shown in figure 12.