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Operation and Maintenance Manual 43
with air as the oxidant in the SCD and oxygen as the oxidant in the NCD.
For the SCD, detector gases must be sulfur free (<1ppb) for proper Detector
operation. In general, bottled air is preferred to “house” air from a compressor
because compressors tend to generate lower quality air. In addition, pressure
fluctuations induced by the air generator may be detrimental to Detector
performance.
For the NCD and GC, use gases that are low in nitrogen and total
hydrocarbons. Use gases with an "instrument" or "chromatographic" purity
rating. Agilent recommends gases with a purity range of 99.995% to 99.9995%.
Do not use oil-pumped supplied air since it contains large concentrations of
hydrocarbons.
Use of appropriate traps on carrier, hydrogen and oxidant sources to improve
support gas quality, such as a sulfur trap gas purifier, is recommended. The
oxidant used to supply the ozone generator should be dry to prevent internal
corrosion. Use of a moisture trap or dryer is recommended.
Two-stage pressure regulators
The combustion gases must be supplied to the Controller at a pressure of
25 psig or less. Use a two-stage pressure regulator rather than a single-stage
regulator to eliminate pressure surges. High-quality, stainless-steel
diaphragm-type regulators are recommended. On/Off valves at the regulators
are useful but are not essential. Mount the valves at the outlet fitting of the
pressure regulators.
If you use gases with a two-stage regulator up-stream, it will be sufficient to
use single-stage regulators at the Detector.
Particle Filtration
Up-stream, inline particle filtration of 10 micron or better is required to
prevent damage to Controller and Burner components.
Supply Tubing for Combustion Gases
Use preconditioned and cleaned copper or stainless steel tubing to supply
gases to the 355 SCD and 255 NCD. Do not use ordinary copper tubing since it
contains oils and other contaminants. Plastic tubing is not recommended since
it is permeable to oxygen and other contaminants that can damage columns
and detectors or cause elevated background. Teflon tubing may be acceptable
in some clean environments.
WARNING
Ozone is a hazardous gas and a strong oxidant. Minimize exposure to ozone by using the
instrument in a well-ventilated area and venting the exhaust of the vacuum pump to a
fume hood. Turn off the ozone generator when the instrument is not in use.