| Abstract: | The gas chromatographic use of flexible thin walled soft glass capillary columns coated with non-polar stationary phases is compared to similar columns made of fused silica glass. With non-polar soft glass columns, the use of surface roughening viagaseous HCI followed by a Carbowax 20 M pretreatment gave adsorptive phenomena, and thermal instability. With very polar soft glass columns where a variety of cyanopropyl silicone phases were coated directly onto the NaCI crystal matrix, adsorptive effects were again prominent and frequent break-down in film stability with time, was also observed. These undesirable effects were due to the presence of metal oxides in the soft glass. Attempts to remove these materials from the thin walled soft glass surface by means of acid leaching produced significant brittleness. This deleterious result was further increased by attempts at high temperature silylation or polysiloxane deactivation. In sharp contrast, the fused silica surface was essentially free of metal oxides and the surface silanol groups are easily neutralized by silylation or polysiloxane deactivation techniques. No brittleness was observed following these procedures. An increasing series of high molecular weight, viscous, polymeric vinyl containing non-polar and highly polar stationary phases have been produced which readily wet the surface of the fused silica and are easily crosslinked in the presence of free radical generators. These columns are essentially free of all the problems noted with flexible thin walled soft glass. When all of the parameters involved in the fabrication of a glass capillary column are assessed, it appears at this time, that the flexible fused silica glass column with cross linked phases approaches the “ideal” capillary column. |
