Gas Chromatography - Injection Devices > Packed Column Injectors > Page 14


Packed Column Injectors

In general, the sample injected onto a packed GC column ranges in volume from 0.5ml to 5ml and usually contains the materials of interest at concentrations ranging from 5%v/v to 10%w/v. The sample is injected by a hypodermic syringe, through a silicone rubber septum directly into the column packing or into a flash heater. Although the latter tends to produce broader peaks it also disperses the sample radially across the column.

Direct injection into the packing constrains the sample into a small volume, but can cool the front of the packing. An example of a septum injection system used for packed columns is shown in figure 7. The silicone septum is compressed between metal surfaces in such a manner that a hypodermic needle can pierce it, but when it is withdrawn the hole is closed as a result of the septum compression and there is no gas leak. The glass liner prevents the sample coming in contact with the heated metal wall and thus, reduces the chance of thermal decomposition.



Figure 7 A Packed Column Injector