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Can any body explain what is pseudo MRM in api systems? and how can we utilize it and when we can choose this mode? How it will helps us in quantification?
I heard about it for the first time at ASMS '04. A group was using it for LC/MS of insulins. Pseudo-MRM is when the triple-quad is operated in MRM mode (with collision gas on and an optimized collision energy), but the precursor and product ion are set to the same value. I would think this would be similar to doing SIM, but the claim was that it had better signal-to-noise than SIM. I have never used pseudo-MRM.
Off the top of my head, I can think of two reasons why it might give reduced noise over SIM. (1) If isobaric interferences were present, and they happened to fragment at lower energies than the analyte, then the collision energy could be set to an energy that would fragment the interferents but not the analyte to any great degree. The interference fragments would then be kicked-out by Q3, but the unfragmented analyte would make it through. (2) If the calibrations for Q1 and Q3 were not exactly the same at a given mass, then the user might inadvertently be doing SIM with a narrower isolation window (tighter resolution) than unit resolution. This same effect could be achieved by simply setting a tighter resolution on a single quad. Using higher than unit resolutions with single- and triple-quads has been shown to give improved S/N in some analyses.
Anyone know of other reasons why pseudo-MRM would be beneficial?
