Supply Tubing For Carrier And Detector Gases - Agilent Technologies 7820A GC Site Preparation Manual

1 7820A GC Site Preparation

Supply tubing for carrier and detector gases

C A U T I O N
C A U T I O N
20
• FID and NPD detectors require a dedicated air supply.
Operation may be affected by pressure pulses in air lines
shared with other devices.
• Flow- and pressure-controlling devices require at least
10 psi (138 kPa) pressure differential across them to operate
properly. Set source pressures and capacities high enough to
ensure this.
• Situate auxiliary pressure regulators close to the GC inlet
fittings. This ensures that the supply pressure is measured at
the instrument (rather than at the source); pressure at the
source may be different if the gas supply lines are long or
narrow.
Use only preconditioned copper tubing (part number
5180-4196) to supply gases to the instrument. Do not use
ordinary copper tubing—it contains oils and contaminants.
Do not use methylene chloride or other halogenated solvent to clean
tubing that will be used with an electron capture detector. They will
cause elevated baselines and detector noise until they are
completely flushed out of the system.
Do not use plastic tubing for suppling detector and inlet gases to the
GC. It is permeable to oxygen and other contaminants that can
damage columns and detectors.
Plastic tubing can melt if near hot exhaust or components.
The tubing diameter depends on the distance between the
supply gas and the GC and the total flow rate for the particular
gas. Tubing of 1/8-in diameter is adequate when the supply line
is less than 15 feet (4.6 m) long.
Use larger diameter tubing (1/4-in) for distances greater then
15 feet (4.6 m) or when multiple instruments are connected to
the same source. Use larger diameter tubing if high demand is
anticipated (for example, air for an FID).
Be generous when cutting tubing for local supply lines—a coil of
flexible tubing between the supply and the instrument lets you
move the GC without moving the gas supply. Take this extra
length into account when choosing the tubing diameter.
7820A GC Site Preparation Guide