18
Hints for Analyzing Dirty Samples
When injecting dirty samples, non-volatile contaminants such as highmolecular weight
compounds, septum particles, derivatization reagents, salts, and pyrolyzed samples adhere to
the interior wall of the injection port liner after the sample solvent and sample analytes have
been vaporized.As this layer of residue thickens, it can cause loss of response for active
compounds. Figure 16 illustrates this effect when highly active phenols are analyzed on a
clean and a dirty inlet liner. In this example, responses are reduced because of adsorptive
effects in the liner.
Non-volatile contamination can be trapped in the injection port liner by using a small plug
of deactivated fused silica or glasswool. Usually a 1cm plug of wool, positioned in the cen-
ter of the injection port liner, is sufficient to provide a surface for non-volatile contamination
to collect. Some instrument manufacturers provide specific instructions on packing injection
port liners tomaximize quantitative accuracy andminimize discrimination. If fused silica
wool or glasswool is used in an injection port liner, it should be replaced as part of the rou-
tinemaintenance schedule for the injection port. Regular replacement of thewool in the
injection port liner will extend the lifetime of the injection port liner aswell as prevent chro-
matographic problems from extensive non-volatile contaminant build up.When replacing
thewool during routinemaintenance, minimize handling of thewool by using awool puller
tool (cat.# 20114).
If fused silica or glasswool is not an effectivemode of trapping non-volatile contamination
under your conditions, injection port linerswith a “cyclo” or glass frit design can be used to
trap non-volatile contamination.While these types of injection port linersmay provide
effective trapping of non-volatile contamination, they are harder to clean than straight injec-
tion port liners packedwithwool.
In the past, some instrumentswere suppliedwith injection port liners that were packedwith
a small amount of packed column packingmaterial.We do not recommend using this type
of injection port liner. Diatomites used in packed columnGC packings often are active and
contain impurities that increase adsorptive effects for active compounds.Also, the stationary
phases that are used in these packings can produce significant bleedwhen used in injection
ports at elevated temperatures.
Guard Columns
Guard columns protect analytical
columns in several ways:
Guard columns trap non-volatile resi-
dues, preventing them from collecting
at the analytical column inlet. These
residuesmay be very highmolecular
weight organic compounds, inorganic
salts, or particles. If these contaminants
enter the analytical column, they can
cause adsorption of active compounds,
loss of resolution, and poor peak sym-
metry.When this contamination begins
to affect sample analysis, a small sec-
tion of the analytical columnmust be
removed to restore proper performance.
Each time a column section is removed,
retention times change, and some reso-
lution is lost. By using a guard column
and removing contaminated loops from
it instead of from the analytical column,
analytical column length and inertness
remain intact.
Guard columns also allowmore injec-
tions to bemade before contamination
interfereswith analytical results.
Because there is no stationary phase
coated on a guard column, the amount
of time the sample spends in the guard
column isminimal. This reduces the
interaction between sample components
and contamination from non-volatile
residue in the guard column.
Formore information on selecting a
guard column for your analysis, request
our
Fast Facts
GCCapillaryColumn
GuardColumns (lit. cat.# 59319).
Figure 16.
Phenols are adsorbed after several injections of a dirty sample.
1. phenol
2. 2-chlorophenol
3. 2-nitrophenol
4. 2,4-dimethylphenol
5. 2,4-dichlorophenol
6. 4-chloro-3-methylphenol
7. 2,4,6-trichlorophenol
8. 2,4-dinitrophenol
9. 4-nitrophenol
10. 2-methyl-4,6-dinitrophenol
11. pentachlorophenol
Initially, phenols respondwell
on a clean, deactivated inlet
liner. However, after several
injections of Southern
Louisiana crude oil, responses
are greatly diminished due to
the sample’s interactionwith
non-volatile residue in the
inlet liner.
1
2
3
4
6
5
8
7
9
11
10
min. 4
8
12
16
15m, 0.32mm ID, 1.0µmRtx
®
-5 (cat.# 10251)
0.2µL split injection of phenols (604 PhenolMix, cat.# 31029)
Oven temp.:
80°C to 290°C@ 8°C/min.
lnj.&det: temp.:
310°C
Carrier gas:
hydrogen
Linear velocity:
45cm/sec.
FID sens.:
16x10
-11
Split ratio:
9:1
1
2
3
4
6
5
8
7
9
11 10
min. 4
8
12
16
MiniWool Puller/Inserter
Makes inserting and removing wool
easy. Not recommended for double
gooseneck liners.
Description
qty.
cat.#
Mini Wool Puller/Inserter
2-pk.
20114
