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Peak Performers
Avoid Septum Problems
By Donna Lidgett, GC Accessories Marketing Manager
✔ Handle septa carefully, to prevent contamination.
✔ Minimize bleed—use preconditioned, low-bleed septa.
Septum Handling
All septa, regardless of their composition, punctura-
bility, or resistance to thermal degradation, will be a
source of problems if they are mishandled. Always
use clean forceps or wear clean cotton gloves when
handling septa; do not handle them with bare fin-
gers, nor with powdered latex gloves—contaminants
such as finger oils, perfumes, make-up, fingernail
polish, skin creams, hand soaps, and talcum can be
absorbed into the septum and will bleed from the
septum during your analyses.
Also, follow septum and instrument manufacturers'
recommendations when installing a septum.
Overtightening a septum nut invariably will reduce
septum lifetime by increasing septum coring and
splitting problems.
Septum Bleed
All septa contain various amounts of volatile materi-
als (e.g., silicone oils, phthalates) that can be
released when the septum is heated to analysis tem-
peratures. Septum bleed occurs when these volatiles
from the septum collect on the column, then elute
from the column and create baseline disturbances or
extraneous (ghost) peaks in the chromatogram. This
problem is prevalent in temperature-programmed
analyses, because the septum volatiles collect on the
column during the oven cool-down and initial hold
periods. Capillary columns require much lower gas
flow rates than packed columns, therefore septum
volatiles are more concentrated, and bleed problems
are more pronounced in capillary GC systems.
Because most GCs are equipped with a septum
purge, septum bleed generally will disappear within
30 minutes after installing a new septum and expos-
ing it to normal injector temperatures. All Restek
septa eliminate this conditioning period because they
are preconditioned and can be used without delay.
Why are Low-Bleed Septa Important?
Either baseline rise or extraneous peaks caused by
septum bleed can interfere with identification and
quantification of target analytes. And, because sep-
tum bleed is inconsistent, method reproducibility
can be a problem. Using low-bleed septa can mini-
mize these effects and help produce more reliable
results.
Why Does Septum Puncturability Matter?
A septum that can be penetrated cleanly and easily
by a syringe needle has a longer life, and consistent
injections made through such a septum help ensure
accurate results. The soft silicone rubber from
which all Restek septa are manufactured is specially
formulated for chromatographic performance,
which ensures our septa are easy to puncture.
What Septum Configurations are Available,
and for Which GCs?
Restek has fashioned septa for all major brands of
gas chromatographs and injectors. Use the septum
size chart to determine the septum diameter for your
instrument, or measure an old septum against the
template if your model is not listed.
Which Septa Should I Use?
Thermolite® septa are a proven low-bleed champion.
With a maximum temperature of 340ºC, there are
very few applications for which Thermolite® septa
are not suitable.
InfraRed™ septa are low bleed septa with a 325ºC
maximum temperature. Even at maximum tempera-
ture, InfraRed™ septa provide long lifetime with little
coring.
IceBlue™ septa are ideal for analysts using inlet tem-
peratures 250ºC or below, or using solid phase
microextraction (SPME) sampling techniques.
IceBlue™ septa will accommodate puncturing from
the large needles used in SPME, and still assure con-
sistent injections and long lifetime.
Thermolite® Septa
• Usable to 340°C inlet temperature.
• Each batch tested with FIDs, ECDs, and MSDs to ensure lowest bleed.
• Excellent puncturability.
• Preconditioned and ready to use.
• Do not adhere to hot metal surfaces.
• Packaged in non-contaminating glass jars.
Septum Diameter 25-pk./price 50-pk./price 100-pk./price
5mm ( 3/16") 20351 20352 20353
6mm ( 1/4 ") 20355 20356 20357
7mm 20381 20382 20383
8mm 20370 20371 — —
9mm 20354 20358 20362
9.5mm (3/8") 20359 20360 20361
10mm 20378 20379 20380
11mm (7/16") 20363 20364 20365
11.5mm 22385 22386 22387
12.5mm ( 1/2") 20367 20368 20369
17mm 20384 20385 20386
Shimadzu Plug 20372 20373 20374
InfraRed™ Septa
• Usable to 325°C inlet temperature.
• Preconditioned and ready to use.
• Excellent puncturability.
• Do not adhere to hot metal surfaces.
• Low bleed.
• Packaged in non-contaminating glass jars.
Septum Diameter 25-pk./price 50-pk./price 100-pk./price
9mm 21417 21418 21419
9.5mm (3/8") 21421 21422 21423
10mm 21424 21425 21426
11mm (7/16") 21427 21428 21429
11.5mm 21430 21431 21432
12.5mm (1 /2") 21433 21434 21435
17mm 21436 21437 21438
Shimadzu Plug 21439 21440 21441
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