Site Preparation
Assembling the gas plumbing
14
Supply tubing
Caution
Do not use methylene chloride or any other halogenated solvent for
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.
Copper tubing usually contains oils and other manufacturing lubricants
which must be removed before use. A methylene chloride rinse followed
by a methanol rinse is suitable except when an electron capture detector
will be used.
The choice of tubing diameter depends upon the distance between the
supply source and the chromatograph and the total demand expected for
the particular gas. When the supply is close to the instrument, 1/8•inch
tubing is adequate.
For long distances, or when multiple instruments are to be supplied from
the same source, or if high demand is anticipated (air for an FID), use
larger diameter supply lines to reduce pressure drop.
Be generous when cutting lengths of tubing for local supply lines; a
relatively long coil of flexible tubing between the supply and the
instrument permits moving the instrument to reach rear cover panels.
Cylinder fitting type and size
Consult your local gas supplier for type and size of cylinder valves. They
are described by CGA (Compressed Gas Association) numbers. Use these
numbers to select compatible pressure regulators.
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