20
Figure 18.
Connect the fused silica line directly to the 6-port valve. Notice a small (5mm)
septum helps determine how far the column is inserted into the valve, preventing breakage
at the column end that could allow shards of fused silica to enter the valve.
Figure 17.
A dual-column configuration splits the sample equally between separate detector systems.
Direct Connection
A union between the purge and trap transfer line and the capillary column bypasses the
injection port, eliminating the problems associatedwith the injection port: loss of sample
through the septum purge, adsorption of active compounds, bleed fromViton
®
O-rings or
septum, and—most important— dead volume. Two direct connections are described
below. The disadvantage of a direct connection is it eliminates the ability tomakemanual
injectionswhen attempting to isolate a chromatographic problem. Therefore, this connection
techniqueworks best for experienced analysts and for instruments that undergo regular
maintenance.
Metal Transfer Line:
This is the easier of the two direct connectionmethods. Using the
transfer line provided by the instrument manufacturer and anMXT
®
low dead volume con-
nector (cat.# 20394, see our catalog), connect the trap to the capillary column. This configu-
ration significantly improves peak shape, compared to injection port connections, especially
with an electrolytic conductivity detector (ELCD).
Fused SilicaTransfer Line:
A fused silica transfer line further reduces dead volume, rela-
tive to the original equipment line.We recommend using Siltek
®
fused silica tubing forVOC
or other sensitive analyses because it is not affected bymoisture and is inert to active com-
pounds. To configure the line, disconnect themetal transfer line from theValco
®
six-port
valve, then remove themetal ferrule and 1/16" nut by cutting the end of the tubing.While
wearing insulated gloves, heat the line to 200°C tomelt the glue that holds the line in place,
then use pliers to pull the line out of the heater jacket. Cool the line, install a piece ofmetal
tubing (cat. #21503, see our catalog) inside the line, then install the Siltek
®
-treated fused sili-
ca transfer linewithin themetal tubing (cat. #10027, page 63). Themetal tubingwill prevent
the transfer line from being scratched or broken. Base the ID of themetal tubing on theOD
of the transfer line: 0.02" ID for a 0.25 or 0.32mm ID fused silica line, 0.30" ID for a 0.45
or 0.53mm ID line. In turn, base the ID of the transfer line on the ID of the analytical col-
umn; we recommend using a transfer linewith an ID equal to or slightly smaller than that of
the column.A transfer linewith an ID slightly smaller than that of the columnwill increase
backpressure, enhancing the resolution of early-eluting compounds. Use a Press-Tight
®
con-
nector (cat. #20400 or 20403, page 20) to connect the fused silica transfer line to the analyti-
cal column (Figure 17). Use the correct ferrule for connecting the column to the 6-port valve
(Figure 18); we recommend a one-piece fused silica adaptor (cat. #20137, page 64).
Angled “Y”
Press-Tight
®
Connector
Septum
Fused Silica
MXT
®
Metal Tubing
(used to protect fused
silica column)
Universal Press-Tight
®
Connectors
Description
cat.#
Universal Press-Tight
®
Connectors, 5-pk.
20400
Universal Press-Tight
®
Connectors, 25-pk.
20401
Universal Press-Tight
®
Connectors, 100-pk. 20402
Universal Angled “Y” Press-Tight
®
Connector, ea.
20403
Universal Angled “Y” Press-Tight
®
Connectors, 3-pk.
20404
For additional connectors, see page 64.
