Markes International Unity 2 User Manual page 40

Flow Path Temp
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Most applications work well with a Trap Low of -10°C. Obvious exceptions to
this include the analysis of samples containing high levels of water or standards
containing unwanted solvent. In these cases it may be useful to maintain a Trap
Low temperature at or near ambient (25-30°C). This allows water and volatile
solvents such as methanol and methylene chloride to breakthrough the trap
(depending on which sorbents are in the trap) and be eliminated from the
system before trap desorption and the beginning of the chromatographic
analysis.
Set the Trap High temperature as appropriate for the trap sorbent and target
analytes. The correct Trap Hold time should ensure all analytes are desorbed
from the trap and that the trap is again clean and ready to use for the next
sample. This is typically set to 3 minutes.
Trap desorption can be carried out split or splitless i.e. if a split is required
during trap desorption (a so-called outlet split, see Section 1.4), check the
relevant box. If the split is selected to be off during trap desorption, all the
analytes will be transferred from the trap to the GC analytical column during
desorption.
The flow through the trap when it is hot = the flow through the GC column plus
that through the split vent, if any.
Set the temperature required for the heated valve and sample flow path by
clicking in the box and typing in the required value. The following general
guidelines may be applied:
All analytes, volatile enough to be present in the air in the vapour phase at
ambient temperature, will pass comfortably through the system with the flow
path between 120°C and 150°C.
For ease of use, extended system lifetime and trace level operation a lower
QUI-1057
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