User`s guide

Troubleshooting
376
Discrimination of Compounds Over a
Wide Boiling Range
Cause: The packing material contained in the trap or in the
sample tube is not suitable for the application.
Action: Ensure that the trap packing selected will
quantitatively retain and desorb all the
components of interest. If no one adsorbent can
cover the entire analyte volatility range, use a
series of two or more adsorbents.
When using two or more adsorbents in the trap,
verify that the order of the adsorbent packing is
in increasing strength. The gas flow through the
cold trap during primary (tube) desorption must
pass through the different packing materials in
order of increasing adsorbent strength, that is
from weak to strong.
Cause: The performance of the system can be impaired if
the cold trap retains more than 10 micrograms (μl)
of water during primary desorption.
Action: By adjusting the inlet split ratio, where
necessary, the amount of water retained by the
cold trap can be minimized.
Action: The amount of water retained in the cold trap
can also be minimized by keeping the trap at a
temperature close to ambient temperature while
using a hydrophobic adsorbent. However, care
must be taken to ensure that the components in
the sample are retained by the cold trap at this
temperature.
Action: Use the reverse dry purge option. See Carrier
Gas Purge of the Sample Tube on page 310.
NOTE: Flows, of helium or hydrogen carrier gas, exceeding 100
mL/min passing through the cold trap during primary
(tube) desorption will adversely affect the retention of
volatile components.
Cause: Discrimination may also result from selective
adsorption or contamination in the system.