User guide

Inlets 8
Advanced User Guide 253
compounds above C
20
were completely recovered and that the
recovery was independent of injection size. Compounds lower than
C
20
were partially vented with the solvent.
Possible adjustments
Depending on what you are trying to accomplish, you have a
number of possible adjustments available.
To eliminate more solvent
• Increase the vent end time, inlet initial time, and purge time.
This will not affect analytes that are quantitatively trapped
but will eliminate more of the solvent peak.
• Increase the vent flow to sweep the liner more rapidly with
the same inlet timing. Increasing vent flow raises vent
pressure if it is set to 0. This puts more solvent onto the
column.
• Raise the inlet initial temperature to vaporize more solvent
and allow more to be eliminated. This also increases the loss
of volatile analytes since their vapor pressures also increase.
To improve recovery of low boiling analytes
• Reduce inlet temperature to lower the vapor pressure of the
analytes and trap them more effectively. This also reduces
solvent vapor pressure and more time will be needed to
eliminate it.
• Use a retentive packing in the liner. Materials such as Tenax
permit higher recovery of volatile analytes but may not
release higher boiling compounds. This must be considered if
quantitation on these high boiling peaks is desired.
• Leave more solvent in the liner. The solvent acts as a pseudo
stationary phase and helps retain volatile analytes. This
must be balanced against the detector’s tolerance for solvent.
An example—continued
The single injection example shown on the last few pages makes
it clear that a 10 μL injection does not overload the glass wool
packed liner. This means that multiple 10 μL injections are
possible.
It was decided to make 10 injections per run, each of 10 μL size.
This would increase analytical sensitivity substantially. No
adjustments were made to improve recovery of the low boilers
since the purpose of this analysis was to detect and measure the
high boiling components.