Page 176 - Illustrated Pocket Dictionary of Chromatography

178 SEPTUM BLEED

Septa are also used for sealing vials. In this case, the septum is lined with PTFE.
The inert liner should be directed so that it is in contact with the sample or sample
vapor. In this case the septum is used with a crimp-cap vial.

septum bleed Septa are made from a wide range of materials (e.g.,
silicon rubber), that may not be fully cross-linked. Therefore, on
heating various volatile components from the septum are released
into the carrier gas flow and may appear as a peak in the chro-
matogram. These materials are all rated to different temperature
levels.
septum purge A slow flow of carrier gas that passes under the
septum and internal to the injector and is used to flush out-gassed
components from the septum (see septum bleed) away from the
column.