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Site Preparation
Gas Purity
28
Some gas suppliers furnish "instrument" or "chromatographic"
purity grades of gas that are specifically intended for
chromatographic use. We recommend these grades for use with
the GC.
Generally, all gas supplies used should 99.995% to 99.9995%
purity or better
(Table
0.5 ppm) of oxygen and total hydrocarbons should be present.
Oil-pumped air supplies are not recommended because they
may contain large amounts of hydrocarbons.
The addition of high-quality moisture and hydrocarbon traps
immediately after the main tank pressure regulator is highly
recommended.
Table 4
Carrier and detector gas purity
Carrier gases
Helium
Nitrogen
Hydrogen
Argon/Methane
Detector support gases
Hydrogen
Air (dry)
4). Only very low levels (less than
Purity
99.9995%
99.9995%
99.9995%
99.9995%
99.9995%
Zero-grade or better
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