User guide

Inlets 8
Advanced User Guide 217
• 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.
After timing a trial set of 10 injections, the total time for the
multiple injection set was measured to be approximately
1.3 minutes. The following timing changes were made:
The result is shown in the next figure. Note the difference in the
vertical scale (5000 versus 500).
Table 42 Modifications
Parameter Increased from To
Inlet Init time 0.3 minutes 1.6 minutes
Vent end time 0.2 minutes 1.5 minutes
Purge time 2.0 minutes 3.0 minutes
Oven Init time 2.5 minutes 3.0 minutes