User guide

Inlets 8
Advanced User Guide 247
If the column is not defined
1 Set up the parameters as described for the defined column
case.
2 Set Tot a l f l ow greater than the column flow plus the septum
purge flow to guarantee adequate column flow.
To develop a PTV method that uses large volume injection
This topic provides a recommended way to change from a
splitless injection using a split/splitless inlet to a solvent vent
mode injection using a programmable temperature vaporization
inlet (PTV). It applies mainly to large volume injections (LVI)
using a PTV, but the concepts can apply to general PTV use. This
topic does not consider all items that can impact an analysis, for
example the liner, solvent, analyte boiling points, or polarity.
This topic also assumes knowledge of your data system—when
to save a method, how to start a run, how to set up a single run,
etc.
The main advantage of the PTV inlet's solvent vent mode is that
you can inject slowly into the inlet, allowing large amounts of
solvent to evaporate in the liner (not in the split vent line). This
concentrates the analytes prior to injection. It requires an
injector with variable speed injections, a “large” syringe, and
knowledge of the sample and the solvent.
When developing a solvent vent method, the goal is to determine
the injection rates and temperatures needed to evaporate the
solvent at the rate it enters the inlet. The development
technique is to gradually scale up to an injection amount that
produces a useful response. The most significant parameters
are:
Tem pe ratur e Hold the inlet temperature at or slightly below the
solvent boiling point until after all the sample has been injected.
This is important so that you do not boil away more volatile
analytes, or boil away the solvent in the needle and trap your
analytes there. An additional point to consider is that the
boiling point of the earliest eluting analyte should be 100 °C less
than the boiling point of the solvent.
Injection speed Estimate the evaporation rate of solvent exiting
the needle based on solvent type, inlet temperature, vent flow,
and pressure. Start with about half that number. Note that you
have to make sure that you configure the syringe properly. If
not, you will over- or under- load the inlet.