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Why use a guard column?
Capillary gas chromatography (GC) guard columns
protect analytical columns by trapping nonvolatile
residues, preventing them from collecting at the
front of the analytical column. These nonvolatile
residues may be very high molecular weight organic
compounds, inorganic salts, or particulates. If these
contaminants enter the analytical column, they can
cause adsorption of active compounds, retention
time drift, loss of resolution, and poor peak sym-
metry. When this contamination begins to affect
sample analysis, a small section of the analytical
column must be removed to restore proper per-
formance. Each time a section of the analytical col-
umn is removed, retention times change, and some
resolution is lost. By using a guard column and
removing contaminated loops from it instead of the
analytical column, the separation power of the ana-
lytical column remains intact.
When should a guard column be replaced?
The guard column should be replaced as it
becomes contaminated with nonvolatile residue. At
this point, the performance of the entire chromato-
graphic system will begin to deteriorate. This nor-
mally is exhibited as a drastic decrease in the
response of active compounds and peak tailing.
What is the life expectancy of a guard
column?
The life expectancy of a guard column depends on
its length, the amount of nonvolatile residue in the
samples, and the nature of samples injected on the
column. When analyzing dirty samples, the guard
column becomes contaminated quickly. Normally,
contamination deposits in the first meter of the
guard column. If a short guard column (1m) is
used, it must be completely replaced when it
becomes contaminated. If a longer guard column
(5m) is used, the contaminated sections can be
removed without having to reconnect it to the ana-
lytical column.
What length guard column do I need?
A guard column should be long enough to keep
non-volatile residue from entering the column, but
short enough so that the analysis time is not dra-
matically increased. Five-meter guard columns are
more cost effective, reduce the frustrations of mak-
ing constant connections between shorter guard
columns and the analytical column. Ten-meter
guard columns often are used when analyzing very
dirty environmental samples. If a very long guard
column (>10 meters) is used, the residence time
of sample components increases, resulting in a
slightly longer analysis time. Guard columns over
30 meters long can cause peak distortion and a
loss in efficiency; they are not recommended. In
any case, it is important to adjust the column flow
rate to account for the length of the guard column
that is used, even though the guard column does
not have retention.
Selection Tips
Several types of guard columns are available. The choice of guard column should be made depending upon
the compatibility of the guard column type with the compounds of interest, or if the tubing is being used as a
transfer line to carry the sample from an inlet device to the column or from the column outlet to the detec-
tor. Choosing a guard column that is compatible with your compounds of interest ensures focused sample
bands, and good peak shape with minimal peak tailing.
Integra-Guard™ Guard Columns
• Continuous length of tubing containing both the
guard column and the analytical column—no
connector required.
• Available in many phases.
• Guaranteed leak-free.
Specialized Deactivations
Siltek™ Guard Columns
Revolutionary deactivation lowers endrin break-
down to less than 1%.
Inertness retained over a wide range of sample pH.
• Minimal bleed.
• Ideal for chlorinated pesticide analysis.
• Individually tested for chlorinated pesticide
breakdown.
Recommended for difficult matrix and reactive
compound analysis
Ideal for use as transfer lines.
• Recommended for use with Rtx®-CLPesticides,
Stx ®-CLPesticides, Stx ®-1HT, and Rtx®-TNT
columns.
Base-Deactivated Guard Columns
• Provides excellent inertness for the analysis of
basic compounds.
• Tested with basic amine test mix (chromatogram
included).
• Recommended for use with Rtx®-5 Amine,
Rtx ®-35 Amine, and Stabilwax®-DB columns
General-Purpose Deactivations
In most cases, the standard IP tubing should be
chosen. The IP surface contains methyl, as well as
phenyl groups, making this surface compatible with
most common solvents.
Intermediate Polarity (IP) Tubing
• The most universal guard column tubing material.
• Phenylmethyl-deactivated surface provides
optimum compatibility for both polar and
non-polar compounds.
Polar-Deactivated Tubing
• Provides optimum wettability for polar com-
pounds.
• Minimizes peak splitting when using polar sol-
vents such as methanol and water.
• Uses a polyethylene glycol deactivation layer.
• Compatible with Stabilwax®, Rtx®-225, and
Rtx ®-2330 capillary columns.
If methanol or water is the primary solvent, then
polar surfaces should be used such as our polar-
deactivated tubing. The polar-deactivated surface is
not resistant to harsh water vaporization, which
occurs when water in the liquid state is injected
onto the tubing surface and rapidly vaporized.
Hydroguard ™ Tubing
• Provides excellent inertness for water-based
samples.
• Reduces effects of dirty samples on column
performance.
• Reduces downtime and maintenance.
Hydroguard™ tubing is preferred for situations
where there is harsh water vaporization. By using a
unique deactivation chemistry, the resulting high-
density surface is not readily attacked after an
aggressive hydrolysis treatment. The high-density
surface coverage effectively prevents water vapor
from reaching the fused silica surface beneath the
Hydroguard™ deactivation layer.
GC Capillary Guard
Column Options
✔ Save money by prolonging the lifetime of your analytical column.
✔ Ensure reproducible analyses by keeping nonvolatile residue from
collecting at the front of the analytical column.
✔ May improve sample focusing and separation efficiency.
by Christine Vargo, US Sales and Distribution Manager