My company just bought a new Agilent 7890 GC equipped with a FID and a 5977 MSD. We also bought the deans switch option. Primary column is ZB-5MS, secondary column is Supelcowax-10. Both are 30 m x 320 µm x 0.25 µm. Effluent from the primary column goes to the flame and the wax is plumbed directly into the mass spec. My question is for anyone who has used their deans switch. Do you have a preference between operating in constant flow or constant pressure mode. If yes, why do you like the option you choose? I have another system that does heart cutting like this but it runs in constant pressure mode, thus I'm more comfortable with that. Mostly, I analyze for very light materials (aroma and flavor is my main game) so living with the fact that the flow decreases throughout my runs has never been a problem for me.