User`s guide

Theory of Thermal Desorption
301
Trap Clean Mode
In Trap Heat mode, a tube is not desorbed. SV2 connects A to B to
supply carrier gas to the Trap-Transfer Line GC column. Only the
cold trap is heated and a GC run is started for conditioning.
Trap Heat mode can be used to condition the trap. Ensure there is an
adequate flow of carrier gas through the trap before beginning a trap
heat cycle.
Tube Conditioning
The Tube-Conditioning mode enables sample tubes filled with an
adsorbent to be heated under controlled conditions for automated
tube conditioning. This removes lower molecular weight impurities
and adsorbed volatiles from the tube before it is used for sample
collection. Depending on the adsorbent and temperatures used, semi-
volatiles can also be removed.
Each tube is sealed into the gas stream, leak tested, and purged of air
prior to heating.
In this mode the cold trap is isolated from the sample tube at all
times. See the following figure.
For optimum tube conditioning, the largest practical volume of gas
should be passed through the tube at the highest temperature that the
sorbent material will tolerate. In most cases, you can use a
temperature 20°C higher than the anticipated normal analytical
desorption temperature.
Example: If you intend to desorb samples at 150 °C, then
condition the tubes at 170 °C at the very least. Sometimes a step-
wise incremental conditioning pattern is used, i.e., 220 °C for 30
minutes, 240 °C for 45 minutes then 250 °C for one hour.
This is a matter of preference. Refer to the manufacturer’s
instructions for detailed information on conditioning specifications
for your sorbent material.
CAUTION
Do not exceed the maximum temperature recommended for
the sorbent contained in the tubes.