User`s guide

Routine Maintenance
245
General Laboratory Cleanliness
Thermal desorption is a very sensitive technique and the adsorbents
used are very efficient trapping agents. If proper precautions are not
taken, the surrounding environment will contaminate your system.
NOTE: All users must be made aware of the circumstances that can
lead to contamination of the system.
The degree to which precautions are necessary depends on the
sensitivity required for your application. Trace level determinations
at ppb levels require substantially more care than determinations at
ppm levels. Background interference can be kept to a minimum if
you take sensible precautions.
Carrier Gas
The carrier gas is a major, potential source of contamination since
any organic volatiles contained in the gas are trapped and
concentrated in the cold trap, and subsequently released when the
trap is heated.
Contamination can originate from the gas itself or from the tubing
used to carry the gas. To minimize the effects of carrier gas
contamination, the cold trap in the ATD/TD is isolated from the
stream of carrier gas except during the desorption processes.
However, high purity gases must always be used.
NOTE: A charcoal filter must be placed in the carrier gas line
close to the inlet to the ATD/TD to minimize the level of
impurities in the carrier gas. Ensure that gas lines
containing filters are protected from excess pressure. See
Connect to the ATD/TD Gas Supply System on page 69.
Remember to replace filters on a regular basis.
Adsorbent Storage
Always store the adsorbents in a clean, dry environment, away from
organic solvents. Adsorbents must always be conditioned before use.
Even when they are kept in a sealed container, adsorbents will trap
and concentrate organic volatiles from the atmosphere.
If you condition the material prior to use, refer to the instructions
provided by the manufacturer.