Restek-2015

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GC COLUMNS
Guard/Retention Gap Columns
it’s a fact
To eliminate leaky connections and to ensure
longer column lifetime, use our unique
Integra-Guard® column. (See )
Vu2 Union® Connector
(See .)
Press-Tight® Connectors
(See )
MXT® Union Connector Kit
for Fused Silica
(See .)
Connectors for Fused Silica Columns
Protecting the Analytical Column
The concept of a guard column is to protect the analytical column from becoming
contaminated with nonvolatile compounds. The guard column is used to retain non-
volatile material, usually in the first 10-20 cm, and not allow it to elute onto the liquid
phase of the analytical column. As the oven temperature increases, the more volatile
target compounds vaporize, elute down the guard column, and refocus at the head of
the analytical column without interference from the nonvolatile material left behind.
Using guard columns is advantageous because they prevent contamination from being
introduced onto the column. Contaminants can cause active sites as well as change the
conditions of the focusing zone of the analytical column. Another advantage is that
the resolution of closely eluting compounds will not be affected when the column is
trimmed during maintenance because the guard column does not contribute to the re-
solving power of the analytical column. Using guard columns is a simple, cost-effective
way to extend analytical column lifetime.
In summary, the retention gap and guard column are essentially the same products,
but are used for different purposes. The deactivated tubing provides an inert path-
way, helps focus target analytes at the head of the analytical column for on-column
and splitless injections, and also prevents nonvolatile material from contaminating the
head of the analytical column.
What type of guard column should be used?
When using a guard column, it is important to match the polarity of the solvent and
the polarity of the surface deactivation. Rxi® guard tubing is good for a wide variety of
applications and allows most common solvents (methylene chloride, hexane, isooc-
tane, toluene) to easily wet and create a uniform film on the tubing surface.
If more polar solvents such as methanol or water are used, a polar-deactivated guard
column is recommended to allow the solvent to wet the tubing surface. However, po-
lar-deactivated guard columns are not resistant to harsh “water vaporization,” which
occurs when water in the liquid state is injected into the tubing and rapidly vaporizes
(such as in steam cleaning). Hydroguard® deactivation is an alternative for direct aque-
ous injections. However, a Hydroguard®-deactivated guard column will not allow polar
solvents to wet the tubing surface and may cause solvent beading if the oven tempera-
ture is 20 °C below the solvent boiling point. Base-deactivated guard columns reduce
adsorption and tailing for amines and other basic compounds.
How is a guard column connected to the analytical column?
To connect the guard column to the analytical column, Vu2-Union®, Press-Tight®, and
other connectors are available. MXT® unions, typically used for connecting metal col-
umns together, are now available for fused silica columns. (See to for
information about these connectors.)