VICI D-2-I - Manual (Page 14)

10
System Requirements
Components Not Included with the Detector System
• Helium (99.999% purity) and other support gases
• Ultra high purity grade gas pressure regulator with stainless steel
diaphragm
• Any special adapters required for connection to the gas regulator
• Flow measuring device
System Purity
Discharge/Carrier Gas Considerations
The performance of the detector is adversely affected by the presence
of any impurities in the gas streams (carrier, discharge, or dopant). We
recommend that a quality grade of helium 5.0 (99.999% pure or better)
be used at all times. Major gas suppliers offer research grade helium
(99.9999% pure) which is particularly low in fixed gas impurities and should
give good results in a clean system, but even the highest quality carrier
gas may contain some water vapor and fixed gas impurities; hence a
helium purifier is included as part of the detector system.
The discharge
gas must always be run through the helium purifier.
Whenever a new batch of discharge gas is received, we recommend
performing a blank GC analysis of the gas in the PDHID mode to detect
and identify the presence of any impurities. Gas purity requirements are
specified in the next section.
Tubing
Standards of cleanliness that are suitable for many GC applications may
be totally inadequate for the sensitive PDHID/PDPID/PDECD work. All
surfaces that contact the gas stream must be glass or stainless steel.
Do not use copper tubing or brass fittings. All tubes must be thoroughly
cleaned and baked before use.
Flow Controllers
The use of valves or flow controllers in which the gas stream is exposed
to any polymer-based packing or lubricating material is to be particularly
avoided.
Pressure Regulators
We recommend commercial “ultra-pure” grade regulators with stainless
steel diaphragms. Regulators with diaphragms made of neoprene or other
elastomers should never be used.