RestekCapillaryColumn InstallationGuide
C. ProtectionAgainst Dirty Samples
Samples that contain non-volatile or highmolecular weight residue can contaminate the
stationary phase, decrease quantitative accuracy, and cause a loss of peak resolution
after a limited number of injections. Packing the inlet sleeve and using a guard column
are two specific precautions recommended to help increase the number of analyses
performed before column and inlet sleevemaintenance is required.
The first precaution involves the use of an inlet sleeve packedwith silanized fused silica
or glass wool (cat.# 20790, 20789) or highly inert silica beads (cat.# 20791) to trap
sample residue and prevent it from entering the capillary column. Insert a loosely packed
2cmwool plug approximately 1cm below themaximum penetration distance of the
syringe needle. Toomuch packingmaterial can detrimentally affect the performance of
the column. Refer to the instrument manual for specific inlet packing instructions.
Stationary phase coated packings are not recommended since they tend to be adsorptive
and can bleed stationary phase onto the column. This problem is particularly damaging if
amethyl silicone inlet packing is usedwith a Carbowax® PEG-type capillary column.
The second precaution
involves using a 5-meter
deactivated, uncoated guard
column at the analytical
column inlet (
Figure L
). The
guard column prolongs column
life by trapping non-volatile
contaminants before they
enter the analytical column.
Sample components travel at
the same rate as the carrier
gas on the uncoated guard
column inlet, but slow down
considerablywhen they reach
the analytical column's
stationary phase. Because the
sample's rate of travel is faster through a guard column, the sample has a limited
interaction timewith residue and, therefore, is not as affected by its presence. Without a
guard column, sample residue affects chromatographic performancemore rapidly due to
increased interaction times. A 5-meter guard column also allows contaminated segments
to be removedwithout having to reconnect the column each time. Restek's
is a built-in guard column configuration that eliminates connectors. For more
information on protection against dirty samples, request Restek's bulletin AGuideWhen
Injecting Dirty Samples.
D. Connecting FusedSilica Tubing
Connectors are necessary to attach guard
columns and restrictors, or to repair broken
analytical columns. Both Press-Tight®
connectors and Vu-Union® connectors are
effective at making low dead volume, inert
connections. Press-Tight® connectors are best
for standard applications at temperatures
below 325°C. Polyimide resin (cat.# 20445)
can be used to strengthen and create
permanent press-tight connections, preventing
the possibility of premature separation. Vu-
Union® connectors are appropriate for high
temperature or high pressure applications, or
when attaching an analytical column to amass spectrometer transfer line. Call Restek's
Technical Service at (800) 356-1688 (ext. 4) for more information on the use of these
two connectors.
