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2007 vol. 3
Tech Tip
Get Connected!
By Al Carusone, Technical Service
Have you ever had to connect a GC analytical column to a guard column or
transfer line? Or repair a broken column? How about connecting two columns
in series or performing confirmation analysis with a single injection? All of
these connections are possible with Restek’s extensive selection of GC connectors.
In most situations, connector choice is a personal preference and Restek offers
several options. Here we review differences among our connectors and answer
some frequently asked questions about our popular Press-Tight® connectors.
The
Press-Tight
®
connector
, a glass connector with a tapered internal diam-
eter at each end, is the quickest and least expensive option. Straight or angled
Press-Tight® connectors are effective for fused silica-to-fused silica connec-
tions for standard applications at temperatures below 325°C. The resulting
connections are inert and have low dead volume.
The
MXT™-Union connectors
are unbreakable metal connectors that are
reusable and ensure a low dead volume. They are designed for metal-to-metal
connections, but also can make metal-to-fused silica unions using a Valcon
polyimide adaptor. This unique graphite-reinforced composite allows a capil-
lary column to slide into the adaptor and be locked in place simply by loosening
and tightening the nuts.
If you require a fused silica-to-fused silica connector for high temperature
applications, try Restek’s
Vu2Union™ connector
or
SeCure™“Y”connector
.
They combine the simplicity of a glass connector with the strength of a metal
connector. Both connectors feature an open design that allows visual confir-
mation of the seal, and also have secondary seals to help maintain a leak-tight
connection. These ultra-strong connections will not disconnect unexpectedly
under temperature changes, vibrations, or other stresses normally encoun-
tered in GC analysis.
Restek also offers a
VacuumVu-Union
®
connector
for connecting a fused silica
column to a mass spec transfer line. The Vacuum Vu-Union® connector uti-
lizes Vespel® ferrules for nonpermeable vacuum connections. A specifically
designed Vu-Union
®
glass insert permits more torque to be applied to the fer-
rules without fear of cracking the insert. As with the Vu2 Union™, you can
confirm the seal through the window of the connector.
What is the difference between angled
and regular Press-Tight
®
connectors?
The only difference between these connectors is their shape.
A Press-Tight
®
connector is a straight tube; an angled Press-
Tight
®
connector has a slight angle in the middle which
reduces the strain on the fused silica tubing. This is of partic-
ular use in making a connection in a broken column, when
you must make the connection within the column coils.
How can I obtain a leak-tight seal using a
Press-Tight
®
connector?
Press-Tight
®
connectors are easy to use, but if they are not
properly sealed, they can loosen due to thermal expansion
during temperature-programmed runs. The keys to successful
sealing are: 1) making a clean, square cut on the column and
2) moistening the end of the column with methanol before
seating it into the connector. A small amount of polyimide
resin also helps prevent the seal from separating during
temperature cycling.
Can Press-Tight
®
connectors be used with
MXT
®
columns?
No. To achieve a leak-tight metal-to-metal connection, we rec-
ommend the MXT™ Low Dead Volume connector for metal
columns. These low dead volume connectors are Siltek
®
treated to make them inert to active compounds, and they
can be used up to 400°C without degrading the deactivation
layer. MXT™ tubing can even be connected to fused silica
tubing using an MXT™ connector with a Valcon Polyimide
ferrule instead of a stainless steel ferrule.
A brown ring indicates
a proper seal.
get the connection
see page 20-21 for a sampling of our connectors,
or visit us online at
www.restek.com