ADV06-15_1-412

12 / 413

10
By Scott Adams
How to Choose a GC Inlet Liner:
Simplify Selection Based on Injection Type
Choosing the correct GC inlet liner is critical in assuring that the
desired amount of sample is transferred onto the column in an effi-
cient manner, without negatively impacting the target compounds.
However, liners come in many configurations that differ in geometric
design, volume, base material, deactivation, and the presence or
absence of packing material. With so many choices available, how do
you choose the liner that’s best for your application? Fortunately for
the user, finding the proper GC inlet liner can be greatly simplified by
basing the decision on injection type.
Split Injections
A split injection is used when the compounds of interest in your sam-
ple are of relatively high concentration or when low limits of detection
are not necessary to achieve. As the name implies, the injection is split
so that a manageable amount of sample is transferred onto the GC
column. Split injections are accomplished by high flow rates through
the inlet, with some flow (and sample) going to the GC column and
some going out the split vent. Since there is a high flow rate, the
time that the sample actually spends within the inlet is minimal. In
order to efficiently and reproducibly get a representative amount of
sample onto the analytical column, the inlet must vaporize and mix
the sample quickly.
Two liners are suggested for split injection based on their ability to
vaporize and mix the sample. The first is the Sky® Precision® split liner
with wool. This liner contains deactivated glass wool that is held in
place by dimples on the inside of the liner. The wool enhances vapor-
ization and mixing of the sample by increasing surface area, and it also
wipes the syringe needle during injection to increase repeatability. The
wool is deactivated in situ, making for a very inert liner that works well
for the majority of split injection applications. However, if your sample
interacts negatively (e.g., compound degradation or adsorption) with
wool, then a Sky® Cyclo liner is recommended for split injections. This
highly inert liner is also treated with Sky® deactivation, but it does not
contain wool. Instead, the bottom third of the liner contains a cork-
screw of glass, which increases the interior surface area and assists
with sample vaporization and mixing.
Splitless Injections
A splitless injection is used when the compounds of interest are pres-
ent at lower levels. With this technique, the split vent is closed at the
start of the injection and all of the flow passing through the inlet is
directed through the column for a programmed period of time. The
split vent is then opened to flush out any remaining solvent vapor. In
a proper splitless injection, 99% of the compounds of interest will be
transferred onto the GC column.
As with a split injection, two liners are recommended for use with
splitless injection. The first is the Sky® single taper liner with wool on
the bottom. The single taper at the bottom of the liner limits the inter-
action of the target analytes with the metal inlet seal and helps direct
or focus the sample to the head of the column. The wool catches the
injected sample and provides a place fromwhich it can vaporize, while
also trapping nonvolatile “dirt” that can contaminate the GC column.
Again, the wool is treated in situ with Sky® deactivation, creating a very
inert liner, which often is needed for trace-level analysis. This liner is a
good choice for the majority of splitless injections. However, if your
target compounds degrade or adsorb on wool, a Sky® single taper
liner without wool is recommended instead.
Sky® Precision® liner with wool for Agilent® GCs
Sky® Cyclo liner for Agilent® GCs
Sky® single taper with wool for Agilent® GCs
Sky® single taper without wool for Agilent® GCs