Gas Chromatography - GC Columns > The Packed GC Column > Supports for GLC > Page 22

 

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In this way the strongly polar silanol groups are methylated and assume dispersive characteristics that do not produce peak tailing. Although the major contributors to adsorption by the support are the silanol groups, a residual adsorption results from the presence of trace quantities of heavy metals such as iron. which can be largely removed by acid washing prior to silanization. All three types of support are commercially available. None of these supports, however, are completely devoid of adsorptive properties and in may cases the effect of the residual adsorption must be further reduced by suitable stationary phase additives.

 

To try to completely eliminate adsorption effects from the support, Teflon was explored as a possible alternative to a diatomaceous earth. Teflon powder proved to have little adsorption, but also proved to be extremely difficult to pack into a column. So difficult, that it is very rarely used in general GLC analyses. Its inert character makes it useful for the separation of certain highly corrosive materials. It has a temperature limit of about 250˚C.

Glass beads have also been used as supports for packed GC columns and, if silanized, have little adsorption properties. Being non-porous, all the stationery phase must reside on the surface of the beads which gives them limited loading capacity. If the loading is increased, the stationary phase collects at the contact points of the spheres and form relatively thick accumulations, producing a high resistance to mass transfer and consequently low column efficiency. Glass beads appears to be the worst compromise between a column packed with modified Celite and a wall coated glass ,or fused silica, capillary column.