Composition of a Capillary Column

FIGURE 1.7 Capillary column trunk under sagittal sectioning. 

The stationary phase of a polar colnmn is composed usually of polar components such as polyethylene glycols or cyano groups. The most used columns are by far the low polarity ones, grafted at 95% with methyl groups and 5% with phenyl groups. 

The compounds of a mixture are mainly separated according to their polarities when the stationary phase is polar and according to their volatility when the phase is non-polar. When faced with a mixed mixtnre, the choice of a low polarity column is usual because the low polarity stationary phases are generally more robnst and more thermally stable than their polar connterparts. GC-MS imposes the nses of low bleeding capillary colnmns (see Section 1.2.2.2). 

It is possible to place a deactivated silica capillary in the transfer line (Section 1.2.3) and to connect the analytical column to the latter. Obstructing this capillary by jabbing it into a septum when changing the column avoids stopping the pumps of the mass spectrometer. Be aware though, as mentioned previously, all press-fit connections constitute potential sources of leakage. 

---