VICI D-2-IM - Manual (Page 12)

8
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 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.