Figure 2:

Illustration of various MS/MS operational modes on a triple quadrupole and related hybrid instruments for enhanced sensitivity with (A) selected ion monitoring (SIM) in which all precursor ions are sequentially passed through the first two quadrupoles (e.g. Q1 and q2 respectively) with subsequent selection of analyte ion in quadrupole three (Q3) without inducing fragmentation of the selected ions, (B) single reaction monitoring (SRM) in which a single precursor ion of interest is selected in Q1 followed by collisional dissociation in q2 and selection of a single fragment product ion in Q3, (C) illustration of two types of multiple reaction monitoring (MRM) operation: (i) multiple fragment selection mode in which a single ion is selected and fragmented as in SRM and Q3 sequentially selects multiple fragment product ions of interest, and (ii) multiple precursor selection mode in which two or more precursor ions are sequentially selected in Q1, followed by collisional dissociation in q2 and selection of a single fragment product ion that the selected precursor ions have in common, (D) parallel reaction monitoring (PRM) in which Q1 and q2 operation is analogous to SRM but Q3 is replaced with a high resolution orbitrap mass analyzer that simultaneously selects fragment product ions, (E) enhanced product ion (EPI) in which Q1 and q2 have analogous operation to SRM and PRM but Q3 is replaced with a linear ion trap mass analyzer where fragment product ions of interest can be accumulated prior to detection to enhance sensitivity.