System Requirements; Components Not Included With The Detector System; System Purity; Recommended Carrier Gas Purifiers - Valco Instruments Co. Inc. TCD Instruction Manual

System Requirements

Components Not Included with the Detector System

System Purity

Recommended Carrier Gas Purifiers

Carrier Gas Selection

•
Carrier gas (99.999% purity is recommended)
•
Ultra high purity grade gas pressure regulator with stainless steel
diaphragm (recommended)
•
Any special adapters required for connection to the gas regulator
•
Flow measuring device
•
Flow regulating device
Since detection of low concentrations depends in part on the purity of the
carrier, the purest carrier available must be used in order to achieve the
lowest possible detection limit. To maintain carrier purity, extra care must be
taken to assure that the delivery system is clean and free of leaks. Use
stainless steel tubing (cleaned to removed manufacturing solvents) instead
of nylon or PTFE tubing, which can diffuse contaminants into the carrier.
The Valco Helium Purifer (product number HP2) and Nitrogen Purifer (product
number NP2), which utilize a rare earth gettering alloy to effectively remove
contaminants, are recommended for ppm level analysis of permanent gases.
For other applications, economical and convenient VICI Mat/Sen purifiers are
appropriate. Order the P300-1 for nitrogen, P200-1 for hydrogen, or the
P100-1 for helium and other inert carrier gases.
The detector's response to a component is based upon the difference
between the thermal conductivities of the component and the carrier gas: the
greater the difference, the greater the response. The table below shows
thermal conductivities for a variety of light gases.
Hydrogen
Helium
Neon
Methane
Oxygen
Air
Nitrogen
Carbon monoxide
Water
Argon
Carbon dioxide
As an example, note in the table that the thermal conductivity of hydrogen is
46 and helium is 37, while nitrogen is only 6 and argon is even lower at 4.
Since the largest difference in thermal conductivity yields the best response,
detection of small amounts of hydrogen is better done with argon or nitrogen
carrier than with helium.
45.9
36.9
11.8
8.6
6.6
6.4
6.4
6.2
4.5
4.5
4.2
7