Gas Chromatography - GC Columns > The Capillary or Open Tubular Column > Static Coating > Page 30


Static Coating

The entire column is filled with a solution of the stationary phase and one end is connected to a vacuum pump. As the solvent evaporates, the front retreats back down the tube leaving a coating on the walls. A diagram of the static coating procedure is shown in figure 16. The column is filled with a solution of stationary phase having a concentration appropriate for the deposition of a film of the desired thickness. Again the required concentration will depend on the stationary phase, the solvent, the temperature and the condition of the wall surface. Unfortunately, the optimum solvent concentration is not theoretically predictable and requires some preliminary experiments to be carried out to determine the best coating conditions.


Figure 16. The Static Method for Coating Open Tubular Columns

After filling, one end of the column is sealed, and the other end is connected to a high vacuum pump and placed in an oven and the solvent slowly evaporates and the front retreats leaving a film of solution on the walls. The solvent then evaporates from this film and the stationary phase remains as a thin coating on the wall. The procedure is continued until all the solvent has evaporated and, except for the stationary phase, the column is empty. This process may take hours to complete. The procedure needs no attention and thus, can be carried out overnight. This procedure is more repeatable than the dynamic method of coating but, produces columns having similar performance to those dynamically coated.