UsingFerruleswithSRI GCs
Brass ferrulesare thepreferredmethod for
sealingmost tubing connectionsand they
canalsobe used on the1/8” stainless-steel
tubingused for packed columns inSRI GCs.
If thepacked column isgoing to be con-
nected toanythingother than the injection
port, slipa stainless ( stainless ispreferred
for temperaturesabove200C since the
brassnutswill discolor ) 1/8” nut over the
end of the column, threaded side facing out.
Then add thebackand front ferrule to the
tubingand tighten asdescribedpreviously.
If theendof the packed column isgoing
straight to the injectionport a 1/8” soft
graphite ferrule shouldbeused instead. Slip
a 1/8” stainless steel nut over the tubing,
threaded side facingout. Placea 1/8” graph-
ite ferruleonto the tubingwith thenarrow
end facing out. Avoidgetting particlesof
graphite inside the column.
Unlike thebrass ferrules, thegraphite ferrule
canbeplaced at variabledistances from the
end of the tubing. This is helpful when posi-
tioning the column in the injector. Also the
nut and ferrule canbe removedand re-
placedwhereas the brass ferrule isdifficult
to remove.Withgraphite ferrulesoneal-
ways has the choice touseeither hardor
soft graphite. Soft graphitemakes thebest
seal but canoutgas organic compounds
whichmay showupasbaseline bleed.
Hard graphite ferrulesbleed less, but are
prone to shrinkageafter the first heating cy-
cle andmay leakasa result.
SRI’sgeneral rule is touse soft graphite
at the injector endof thecolumn and
hardgraphite at thedetector end.
Page 4
Stainless nut
withbrass ferrule
Soft graphite
ferrule
