Capillary Chromatography - History of Capillary Columns 4
During the period of soft glass capillary use the optical fiber industry had developed methods for drawing flexible quartz fibers by coating then directly after drawing with a temperature resistant polimide plastic. The product was quite unique in that loose knots could be tied in such fibers without their breaking and yet the natural form of the fibers was straight. The technique for quartz fiber production was used by Dandenau (3) to produce flexible quartz capillary tubes. As the quartz capillaries were intrinsically straight they could be easily connected to the sample injection system and the detector using appropriate ferules but, at the same time, the column itself could be formed into a neat coil to fit into a relatively small oven. Initially, some minor problems were experience in coating these columns, but these were soon over come and today, most stationary phases can be coated as thin films on the walls of quartz capillaries. An example of a chromatogram from a fused silica column is shown in figure 3. The extremely high resolving power that can be obtained from the fused quartz capillary is clearly demonstrated.
Fresh-drawn, uncoated, thin walled capillary tubing is strong and flexible but if exposed to water vapor (e.g., moist air) it quickly becomes weakened and extremely brittle. In the production of the fused silica capillaries, the external surface is coated with a polymer which prevents moisture reaching the surface and the material is kept strong and flexible. Soft glass tubing can be drawn to the same dimensions but, again, if not coated becomes brittle and friable. Ogan et al. (5) used the same technique of polymer coating with soft glass tubing (but drawn at a much lower temperature) and produced a very similar type of capillary tubing.
Figure 3 The Separation of a Sample of Regular gasoline on a Fused Quartz Capillary Column.