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- Posts: 25
- Joined: Sat Apr 09, 2022 4:08 pm
In recent days I've been playing a little more with both SIM and MRM methods for the detection of a set of specific chemical compounds at trace levels using an Agilent GC-QqQ instrument. Traditionally, SIM and Scan methods have always been used for the detection of these compounds, but I wanted to give MRM a try, partly as a learning opportunity (I'm curious) and partly so I can see for myself the relative sensitivities of MRM v SIM methods. I also like the novelty of baselines of nearly zero.
One thing that has always been drummed into me about MRM is that "thou shalt not select product ions which are also present in your precursor ion list", presumably to eliminate interferences with near identical m/z to the precursor, although any further explanation of this would be much appreciated.
This is all every well in theory, but in practice the smallish (~170-240 m/z) molecules I'm looking at have a tendency to fragment into very specific ions many which are common to both the precursor and product ion list which is a bit of a problem as it leaves me with a much smaller list of potential product ions many of which are not terribly abundant.
Because of what I'm doing, I'm trying to maximise sensitivity and to be quite honest, the selectivity which MRM brings to the mix is not terribly important as after all, I'm comparing the method directly against SIM where the interferences alluded to in texts on the subject are 'par for the course' and thus can't be more of a problem with MRM than they are already.
As people with far more experience of this than me, is including ions in the product ion list which are also precursor ions that big of a problem? I would love to know your thoughts?
Kind Regards
TD2