User guide

248 Advanced User Guide
8 Inlets
Vent end time The vent end time setpoint must be greater than
the time the needle spends in the inlet. If the vent time is too
short, you will overload and contaminate the column and inlet.
Adjust the vent time as you scale up the method.
If using a PTV with an MSD, another tip for method
development is to scan for solvent ions. Detecting the solvent
ions can be useful in troubleshooting residual solvent bleed onto
the column.
To develop a PTV method for large volume injection, try the
following:
1 Determine a small injection volume that works on a
split/splitless inlet in splitless mode or the PTV in splitless
mode. Choose a volume that does not currently overload the
inlet.
2 Start with a 5–10 uL syringe and make sure the syringe is
properly configured in the instrument and data system.
3 Make sure the column is configured.
4 Set up the inlet to perform a 1 uL injection.
Use the splitless method conditions, except:
• Start with the inlet temperature cold, near but slightly
below the solvent boiling point. For example, if using
methylene chloride (boiling point 39 °C), start with a
temperature of 30–39 °C.
• Use Splitless mode.
• Ramp to the normal splitless inlet temperature.
5 Note the response achieved.
6 Next, change the inlet mode to Solvent vent.
7 Check the injector timings.
a Install an empty sample vial in the injector turret or tray.
b Input the injection rate (Sample Draw Speed, Sample Disp
Speed, and Inject Dispense Speed rates) for the injector and
increase the injection volume to 5 uL.
c Enter draft Solvent vent parameters:
• Set a Vent flow of 100 mL/min as a starting point.
• Keep the inlet isothermal for now.