User`s guide

Troubleshooting
371
this is the source of the problem, proceed as
follows:
1. Desorb a clean blank tube for two minutes, then
desorb the cold trap and monitor the resultant
chromatogram.
2. Extend the primary desorption time to 5 minutes
and repeat the experiment.
3. Continue to extend the desorption time in this
manner to determine whether the contamination
increases with the time that the trap is exposed to
the gas flow.
4. If the level of background contamination
increases with desorption time, then the carrier
gas supply may be at fault and the various
components of the supply system should be
checked.
5. One of the simplest ways to test the gas supply is
to temporarily eliminate the laboratory gas lines:
Install a fresh cylinder of gas as close as possible
to the TD/GC system using clean copper or
stainless steel tubing.
Cause: Contamination is coming from the filter disks.
Action: If the gas supply is found to be clean, the
contamination may be coming from the flow
path upstream of the cold trap and within the
TD. In this case, examine the filter disks for
cleanliness. If in doubt, replace the filter disks
in the mobile and fixed seal of the TD and ATD.
See Changing the O-Rings in the Fixed and
Mobile Seals on page 249. Also replace the
filter disks located at both ends of the cold trap.
See Changing the Trap Filter Disks on page
281.
Cause: Contamination is coming from the sample tubes.
Action: Examine the sample tubes for cleanliness.
Sample tubes must be reconditioned as
described in Tube Conditioning on page 301.
Cause: Compounds trapped on the vent filters will tend to