Chromatography Forum

Hello fellow chromatographers,

I'll preface this by saying I'm using MassHunter GCMS Acquisition software (I think) - it's attached to a 5975T LTM GC/MSD system. I'm referring to problems I have when I try and edit the mass spec method in the Single Quad MS method parameters window. Hope that's enough info on the software (and hardware!)

I was wondering if you could give me a hand to a question I'm sure is easy enough to answer. I'm trying to set up a SIM method for an analyte, I've created the grouping of 5 ions (and am starting with a dwell time of 50 each) but the instructional guide seems to think I can set the time at which the SIM mode kicks in. Whether I have the mode as SIM only or Scan and SIM the time segment cannot be adjusted, it stays linked to the solvent delay (4 min), if I change the solvent delay to the time I actually want (around 10.50) then it alters, but I don't really want to do that. Is there any way of overriding this, as surely I should only be monitoring the ions in the window where I know my peak occurs? Last time I tried to run the SIM method given to me it looked God awful.

Any help would be appreciated,
Many Thanks,
Emily

Hi Emily,

I have been running SIM methods through Mass Hunter on a 7000QQQ and it should be similar to what you are doing on the 5975. I am pretty sure your first time segment will begin at the end of the solvent delay. If you use a second time segment the first will end when you put in the beginning time for the second, and so on for each segment you have. You don't put in ending times, only the beginning time for the next segment.

You will either have to set a time segment that collects those ions for the full run or set a solvent delay right up until before it elutes then use a time event for MS-OFF after the peak. Unless your background is really noisy though, it should not make much difference in file sizes if you acquire data for the full run or not.

Hi James,

Just wanted to follow up saying that solvent delay at 4 min worked fine and has provided an ever so slight increase in sensitivity! Thanks for your help - must have been the SIM/Scan mode that screwed it up first time.

Emily