RestekCapillaryColumn InstallationGuide, Section II
Table I Typical FID FlowRates
Instrument
H
2
(ml/min.) Make-up (ml/min.)
Air (ml/min.)
Hewlett-Packard
30
20
400
Varian
30
20
300
Shimadzu
30-60
40
500
PerkinElmer
45
--
450
II. ColumnMounting and Installation
Donot remove thehigh-temperature
stringholding the fused silica capillary
column inside theRestek cage
. The high-
temperature string is capable of withstanding
more than 400°C and does not decompose
during continuous operation at oven
temperatures used in capillary
chromatography.
When hanging the column on the oven support
rod, be careful that fused silica tubing does not
contact anymetal parts. Stainless steel
columns can be placed directly on the oven support rod. If there is not an oven support
rod, one can bemade by inserting a temperature resistant pegboard hook into the
corrugated ovenwall or by hanging a 1/16-inch "S" hook from the oven ceiling. Be
careful not to damage the oven thermocouple or interferewith the fan operationwhen
installing homemade brackets.
Position the column so that it ismidway between the injector and detector. This reduces
thermal gradients and enhances retention time reproducibility. Uncoil one or two loops
of tubing. When using fused silica columns, be careful not to scratch the column surface
against themetal cross bars when removing loops. This abrasion of the polyimide
coating could lead to spontaneous breakage.
Caution
-When removing loops from 0.53mm ID columns, pull the tubing from the
cage at the point with thewidest gap between themetal crossbars. Avoid sharp bends
that will break the tubing.
Choosing Ferrules
Graphite or Vespel®/graphite ferrules are used to seal the column
to the injector and detector in capillary gas chromatography. Both
ferrule types have advantages and disadvantages. Graphite
ferrules are the easiest to use, and they are leak-free, universal
for most systems, and preferred bymost beginning capillary chromatographers.
Because graphite ferrules are soft, they easily conform to column outside diameters and
different types of instrument fittings. However, they can flake or fragment upon
removal, causing particles to lodge in the injector or detector sleeves, and theywill not
hold a seal under vacuum. Vespel®/graphite ferrules are hard and theymust match the
column and fitting dimensions closely to seal properly. In addition, because Vespel®/
graphite ferrules can deform during initial heating, they need to be re-tightened or
leakagewill occur. Vespel®/graphite ferrules do not fragment, can be reusedmany
times, and are preferred bymass spectroscopists since they do not contaminate the ion
sourcewith particles andmaintain their seal under vacuum. In all cases, it is best to
choose a ferrule that fits snugly or is slightly larger than the capillary tubingOD (see
table below). Thisminimizes the need for excessive torque to properly seal the ferrule
to the column.
