5
Uniliner
®
direct injection liner (D or E) connects directly to the column inlet, responses for
both active and highmolecular weight compounds are greater than for any of the splitless
injection liners. There is little difference between responseswhen using aUniliner
®
direct
injection liner (D) or aCyclo-Uniliner
®
liner (E). Both liners direct all of the sample onto the
columnwhileminimizing contact between the vaporized sample and other injection port sur-
faces. However, aCyclo-Uniliner
®
liner or aUniliner
®
containing deactivatedwool always
should be usedwhen injecting dirty samples.
Injection Port Setup for Direct Injection
Types of injector liners used in direct injection systems
Restek carries three styles of direct injection liners (Figure 3). Of these, the buffer volume
chamber in standardUniliner
®
injection port liners (A) will accommodate the largest sample
vapor cloud. Because of the open design, samples should be relatively clean, otherwise con-
taminants could be delivered into the column inlet. For extremely dirty samples, open-top
Uniliner
®
injection port liners (B) can be packedwith deactivated fused silicawool to trap dirt
and non-volatile sample residue. Contaminatedwool can be replaced easily and the liner
cleanedwith solvent and a nylon brush. The glass spiral in aCyclo-Uniliner
®
injection port
liner (C) provides a surface for vaporizing high and lowmolecular weight compounds. Non-
volatile sample residue is trapped on the first turn of the spiral, reducing subsequent interac-
tion between that contamination and the rest of the sample. In comparisonwith liners packed
withwool, aCyclo-Uniliner
®
injection port liner will accept up to five times asmany injec-
tions of dirty samples before calibration curves degrade. Each of theseUniliner
®
designs
incorporates a gradual, press-tight taper in the base of the liner, which forms a positive seal
with the column end and prevents sample components from interactingwith heatedmetal sur-
faces in the injection port. The seal of the column into the press-tight taper of the injection
port sleeve is the key to obtainingmaximum responses for all analytes andminimizing sol-
vent peak tailing.
Converting a split/splitless injection port to direct injection
Themost common problems associatedwith splitless injections are caused by the absence of
a direct, physical connection between the injection port liner and the column inlet (Figure 2).
Sample vapor that accumulates in the space around the inlet of the column is exposed to hot,
catalyticmetal surfaces of the injection port. Excess sample vapor and less volatile high
molecular weight compounds also can be swept out the split vent during the purge onmode.
Bymaking a leak-free connection between the injection port liner and the inlet end of the col-
umn via the press-tight taper, contact between the vaporized sample and themetal surfaces of
the injection port is eliminated and the loss of sample out of the split vent is prevented.
Figure 3.
Choose a direct injection liner based on sample characteristics. The buffer
volume chamber accommodates the sample vapor cloud and prevents
sample components from contactingmetal injection port surfaces.
C
B
A
D
A) StandardUniliner
®
Injector Liner
Accommodates large, relatively clean samples.
B) Open-TopUniliner
®
Injector Liner withWool
Ideal for extremely dirty samples.
C) CycloUniliner
®
Injector Liner
Excellent for high and lowmolecular weight compounds; acceptsmany injections of dirty samples.
D) DrilledUniliner
®
Inlet Liner
The drilled hole in aUniliner
®
injection port linermakes direct injection possiblewithEPC systems
by equalizing pressure in the injection port.
