Page 175 - Illustrated Pocket Dictionary of Chromatography

SEPTUM 177

¢
a= ¢ k 1
k 2
Per this definition, a is always greater than or equal to 1.

septum A component that is used to allow a syringe to enter a con-
tainer and withdraw/input material but prevent gas from entering or
escaping after the action is complete. Septa are also used in sample
vials. For HPLC and GC the septa are commonly PTFE clad to prevent
the sample solvent from extracting material from the support mate-
rial. Septa are also used in headspace vials. Finally, septa are used in
GC injector ports and permit the injector syringe to place the sample
in the injector port (or on the column) and yet prevent gas from escap-
ing through the septum. Common materials of construction include
silicone rubber and PTFE-lined silicone rubber. These septa must
be temperature inert because injector temperature are often held at
200°C or higher.

Typical GC injector inlet septa. These are not typically lined with PTFE or any other
material. The correct polymer must be stable at the maximum injector port tem-
perature used in order to minimize bleed.