We're using an HP6890 GC s/dual split/splitless injectors and dual FIDs for TPH work. When using the pulsed splitless injection technique I get alot of variation in the RTs of my first 2 compounds, toluene and nC8. Also, the width of the solvent peak varies from run to run. The RTs of the late eluting compounds are stable. Has anyone seen this before? Do you have any helpful suggestions?
Thanks

Possibly a problem with leakage from the septum. Do the area counts vary or is it just retention time? High pressure injection can cause more problems than usual with leaks around the ferrules and O-rings in the injection port, and also leakage back through the syringe plunger, although these leaks tend to be more constant. If you are using the fast injection mode without a dwell time in the injection port, there is probably leakage through the septum before it reseals. Try leaving the needle in the injection port for 5 to 10 seconds and see if things improve.

Thanks for the response. We change the septum daily, and we use H2 as the carrier gas, so if the 6890 even suspects a leak it shuts itself down. The area counts are relatively stable, the height and RT shift alot thouugh. A number of us have been working on this for a while, so I'm pretty sure we don't have any leaks. I'll give the dwell time a try.

Craig make sure you're inj temp is @ least 285c
I use h2 for TPH analysis and don't have the problem. you may have to high of a pulse. If you still have the problem respond back. Good luck