Gas Chromatography - GC Columns > Column Packing > Page 26

However, straight columns are clumsy to use and occupy a large amount of space which is often difficult to thermostat. The coiled column although more difficult to pack has been readily accepted due to the compact nature of their design. To obtain adequate efficiencies, however, a special packing procedure had to be developed. The apparatus used is shown in figure 13.

Figure 13 An Example of a Column Packing Apparatus


The packing is placed in a reservoir attached to a gas supply that forces the packing through the column. The column exit is connected to a vacuum pump. A wad of quartz wool is placed at the end of the column, constrained by a small restriction, that prevents the wad from being sucked into the pump. The vacuum and gas flow are turned on simultaneously and the packing is swept rapidly through the column. This causes the material to be slightly compacted along the total length of the column and has been shown to produce well-packed columns. The procedure is a little tedious and the success rate is sometimes less than 90%. In addition, the process does not lend itself to automation.

The difficulties involved preparing packed columns have also contributed to the preferential popularity of the open tubular columns. The production of capillary columns can be largely automated and several columns can be prepared simultaneously. Another example of a chromatogram from a 40 ft packed column 2 mm I.D., this time of a "benzole" mixture is shown in figure 14.