Shock loops to prevent purijer breakage can be
made by bending 1/8" tubing into a coil shape.
It is essential to use clean chromatographic grade tubing prior
to installing a GC. Tubing can contain residual hydrocarbon
contamination from the drawing process. These contaminants
can migrate into the gas stream causing elevated background
noise and increase instrument down time. Tubing can be
solvent rinsed with methanol or other various solvents that do
not provide a response on the detector being used. (Caution:
do not usemethylene chloridewhen usingECDs.) Restek
offers a full line of pre-cleaned, heat treated tubing to plumb
GCs without the need for solvent rinsing (see page 16). GC
manufacturers recommend copper or stainless steel tubing for
plumbing gas lines between the gas source and the instrument.
Plastic tubing material such as Teflon, polyvinyl chloride, or
Tygon should not be usedwhen plumbing GCs since these
materials will allow air and water to diffuse into the gas lines.
In addition, plastic tubing can give off organic impurities
which can cause ghost peaks and baseline instability.
Tubing Cutting and Bending
The first step toward leak free plumbing is correctly cutting
and bending the tubing. Either a hand-held or a motorized
tubing cutter can be used to cut tubing. With a hand-held
device, the tubing is scored by guiding a cuttingwheel along
the outside surface of the tubing. By increasing the pressure,
the cuttingwheel is forced into the tubing, therebymaking a
cut.With amotorized cutter, the cuttingwheel is driven by a
high speed motor and the tubing is hand-fed onto the spin-
ningwheel. Themechanical cutter*, thoughmore expensive,
will easily pay for itself when plumbing several instruments
since it is faster and makes a clean, open cut.
* Catalog number 20186 is recommended for 1/16” and 1/8" tubing only.
\
Toplace an order, call
1
customer service or
i
i:
your local distributor
When using a tubing cutter, a burr or ridgewill form on the
tubing end. This burrmust be removed to allow unobstructed
gas flow and to obtain a leak-free connectionwith the
compression fittings. Use a file or exterior deburring tool to
remove the burr on the outside of the tubing and an interior
deburring tool for the inside. Restek also offers a special tool
that deburrs the inside and outside of tubing simultaneously
(cat.# 20134 for
l/4”
and 1/8" tubing, or cat.# 20188 for
1/16” tubing). Always hold the tubing open end downwhen
deburring to prevent fragments from falling into the tubing.
Small tubing cutters
allow cuts to be made in tight
places (cat.# 20184)
Tubing Benders
Tubing often requires bending during installation. Copper
and thinwalled1/8"” stainless steel tubing can easily be bent
by hand. However, heavywalled 1/8 and 1/4" stainless steel
tubingwill require a tubing bender. A tubing bender incorpo-
rates the use of lever arms that reduce the force required to
bend the tubing. Bends should bemadewith a uniform radius
and should not kink or deform the tubing in amanner that
obstructs flow. Try the bending procedure on some spare
tubing first to help avoid costlymistakes on expensive
tubing.
7
7
1998
