Help with PID detector picking up too much aliphatic signal

[rycar88]

Hello all - I'm using a PID/FID detector setup for aromatic/aliphatic ratio compound analysis on my GC systems and I've noticed that even though we are using the PID to isolate aromatic compounds for detection, it seems to be picking up everything we have in our standards. The peak-height ratio between Alkanes/Benzenes is about the same between my FID detector and PID detector and when I subtract PID range responses from the FID range on dirty samples to give an adjusted aliphatic result, I always get a huge negative number. I'm using a CPI Int. 10.0 eV lamp connected to a OIC 4430 Lamp Power Supply. This should cut the ionization potentials for these alkanes off (well, most of them), but even if they do reach ionization they should have a depreciated response compared to the benzenes, which ionize much more easily, right? My only hunch is that the lamp is running at a higher energy than it should be (possibly because I'm using a lamp and power supply from different manufacturers) but I'm not sure how to fix that if it is. Anyone have advice for how I can troubleshoot this?

Thanks

[Yama001]

I believe an 8 volt lamp is available to reduce the alkane ionization a bit, though I had always used the 10 volt lamp.