By Anonymous on Thursday, August 7, 2003 - 08:30 am:
Is it possible that ONLY daughter ion shows in single quadrupole LC.MS with tiny molecular ion?
Thanks in advance!
By Anonymous on Thursday, August 7, 2003 - 08:34 am:
It can happen if a lot of in-source fragmentation occurs.
By Anonymous on Thursday, August 7, 2003 - 09:10 am:
It happens when tuning the compound, too???
By M_Gardner on Thursday, August 7, 2003 - 11:28 am:
I've seen some fragile compounds show only fragment(s) when running under usual default settings. Even if you optimize your lenses to maximize the molecular ion, it's still possible to have the fragments exceed the molecular ion, but I've not seen this happen too often.
Are you sure these ions are coming from your compound of interest?
By Anonymous on Thursday, August 7, 2003 - 12:15 pm:
There was a method to run the sample with APCI+(0.1%TFA). Now it's changed to ESI+. A large peak (about 14 units smaller) appears while no molecular peak is obviously observed.
Any futher thoughts?
By M_Gardner on Thursday, August 7, 2003 - 02:20 pm:
It's possible that you're not ionizing your compound of interest. The -14 peak could be a contaminant that ionizes easily. For fragments, typically loss of 18 (water) is the smallest you'll see. A couple of reasons for lack of ionization: (1) The compound might not be amenable to ESI(+). What are its polar functional groups? (2) TFA suppresses ionization in ESI (both polarities) but in my experience doesn't bother APCI(+).
By Anonymous on Thursday, August 7, 2003 - 04:02 pm: