6
AUniliner
®
direct injection port liner can be directly substituted for a split or splitless injec-
tion port liner, quickly and easily adapting the injection port for use in the direct injection
mode.AUniliner
®
direct injection port liner is installed in the samemanner as a splitless
liner, but it must be operated continuously in the purge offmode. Uniliner
®
injection port lin-
ers are available for awide variety of instruments, and aremanufactured to the exact external
dimensions specified for the split/splitless liners they are designed to replace.
Converting a packed column injector to direct injection
A
1
⁄
4
-inch packed column injection port configured for on-column injections easily can be con-
verted for direct injections onto 0.32mm or 0.53mm ID capillary columns by using a specially
designed glass liner that forms a seal with the column inlet. Conversion of a packed column
inlet is accomplished in less than 15minutes.
Note that only packed column injectors with an
on-column configuration can be retrofittedwith these liners.
We offer two injection port conversion kits in our chromatography products catalog: 1)A
glassVu-Tight
®
injection port liner fits directly into a
1
⁄
4
-inch packed column injection port
and allows visual confirmation of the connection between the injection port liner and the
inlet of the capillary column (Figure 4). 2)A
1
⁄
4
-inchUniliner
®
sleeve adapter is fitted into a
1
⁄
4
-inch injection port.A 5mmUniliner
®
injection port liner can be inserted into the adapter in
either direction to allow direct or on-column injections (Figure 1 on page 3). Both conver-
sion kits incorporate the press-tight connection between the injection port liner and the inlet
of the column. The combination of a sample expansion chamber and a leak-free connection
between the injection port liner and the column delivers superior chromatographic perform-
ance. Direct connection of the liner to the column inlet alsominimizes dead volume, reduc-
ing solvent peak tailing and sharpening peaks for early-eluting components.
Either theVu-Tight
®
injection port liner or theUniliner
®
sleeve adapter with liner will fit
Agilent,Varian, or other commonGCswith
1
⁄
4
-inch packed column injection ports. Either
0.32mm or 0.53mm ID fused silica columns can be usedwith either conversion kit, as long
as the tubingOD is 0.4mm or greater.A special high-temperature deactivating procedure
creates an inert surface in the liners, so theywill not absorb or react with active compounds
such as pesticides, phenols, acids, or basic compounds. Liners that incorporate a glass
spiral are available for either conversion system and should be used for the injection
of dirty samples.
Careful – don’t crush the column end!
Frequently, analysts setting up a direct injection system for the first timewill crush the col-
umn end into the Press-Tight
®
taper.When a column is installedwith a new graphite ferrule,
excessivemovement of the column into the Press-Tight
®
taper will crush the end of the col-
umn and force fused silica particles into the column bore. In order to limit themovement of
the column and prevent damage, the ferrulemust be seated in the fitting before the column is
installed all theway into the Press-Tight
®
taper. To properly install a column in a direct
injection liner, withdraw the column end several millimeters away from the Press-Tight
®
taper and tighten the ferrule into the fitting until the column end no longermoves forward
into the liner. The ferrule is now seated and conforms to the interior dimensions of the fit-
ting. Next, loosen the ferrule and push the column into the liner until it seals against the
Press-Tight
®
taper.A dark brown ring at the tip of the columnwhere it contacts the inside
surface of the injection port liner indicates a good seal. Now, when the ferrule is retightened,
the column endwill not be crushed against the liner. Figure 5 shows a column properly
installed in aVu-Tight
®
liner, and a column that has been crushed because the ferrulewas not
seated first.
Detector Setup for Direct Injection
Use ofmake-up gas with a direct injection system
Most flame ionization detectors (FIDs) do not function optimally unless they are supplied
with approximately a 1:1 ratio of carrier gas and hydrogen fuel. Becausemost columns used
in direct injection systems operate at a carrier gas flow of between 5 and 10cc/min., make-up
gasmust be added to augment the low carrier gas flow.
2
Make-up gas improves peak shape,
andmay reduce detector noise and improve linearity. Similarly, electron capture detectors
(ECDs) require up to 100mL ofmake-up gas to improve sensitivity and linearity.
Figure 5.
Good vs. poor column installation
in aVu-Tight
®
liner.
good installation
A brown ring indicates a good press-tight seal.
poor installation
Failure to seat the ferrule before connecting
the column leads to a crushed column end.
Always seat the ferrule before
connecting the column
Figure 4.
Vu-Tight
®
injection liner—in a
1
⁄
4
-inch
packed column injection port—allows
visual confirmation of the liner-column
connection.
oven
ceiling
Press-Tight
®
connection is
visible
PerkinElmer FIDs do not usemake-up gas.
