Chapter:
INJECTORS AND GAS VALVES
Topic:
Near-Ambient Temperature Septum Nut Assembly For Heated Injectors
All SRI Instruments heated injection
ports
are equipped with a specially-designed septum nut
whichdissipates any heat that could be transfered from the heated injection port body (including
split-splitless configurations), to the septum nut and septum by contact. Experience indicates that
when injection ports are permitted to transfer heat to the silicone septum, that septumbleed canand
does occur. Septum bleed is the volatization under heat of silicone oils used in the manufacture and
formulation of today' s
high-performance, resealing silicone septa.
~/
Graphite
reducing ferrule
Capillary
analytical
column
Insulated injection port
liner heating assembly
View of fully-assembled
heated injection port
Glass injection port liner (user-supplied)
:
:::::::: ::;
~
Exploded view of disassembled
heated injection port assembly and
special
septum
nut hardware
Heatsunk
septum nut
extension
Column oven wall (861OC)
Special capillary
column adapter for
on-column injection
Special near-ambient
temperature
"ptum~-----~f~E3~~lillliiiii'E;V~~
nut assembly
Split vent (on
"<,
split/splirless
injector-equipped
models)
Silicone bleed produces
numerous interference peaks
in
chromatograms when the septum
exceeds 180·C and oil vapors are
swept
into
the column and quantitated.
This situation is undesireable and
easilyavoided when the special
septum nut is used.
cq§~I~~
Silicone septum
Only
the injection port hardware within
the column oven
is
heated directly
Cut-away view of assembled heated
injection port assembly
n·-.
....
."
.
')--'
Note the position of the analytical column
within the capillary column adapter and its
position with relation to the septum and
injector liner
The special septum
nut assembly illustrated above
keeps the septum at an adequate
distance from the heated injector
assembly
to
maintain
the septum at
or near ambient temperature with the assistance of the additional mass of the septum nut extension.
This prevents any silicone oils present in the septumfrom volatizing and being carried into the
column. This feature maybe retrofitted onto earlier versions of the SRI GCheated injection
port,
as
only two new
parts
are required. The following page contains chromatographs that illustrate the
effect of this new injector design
