Selected reaction monitoring

[1] A general case of SRM can be represented by where the precursor ion ABCD+ is selected by the first stage of mass spectrometry (MS1), dissociates into molecule AB and product ion CD+, and the latter is selected by the second stage of mass spectrometry (MS2) and detected.

[2] Consecutive reaction monitoring (CRM) is the serial application of three or more stages of mass spectrometry to SRM, represented in a simple case by where ABCD+ is selected by MS1, dissociates into molecule AB and ion CD+.

[6] Following ionization in, for example, an electrospray source, a peptide precursor is first isolated to obtain a substantial ion population of mostly the intended species.

Using isotopic labeling with heavy-labeled (e.g., D, 13C, or 15N) peptides to a complex matrix as concentration standards, SRM can be used to construct a calibration curve that can provide the absolute quantification (i.e., copy number per cell) of the native, light peptide, and by extension, its parent protein.

[9] In 2017, SRM has been developed to be a highly sensitive and reproducible mass spectrometry-based protein targeted detection platform (entitled "SAFE-SRM"), and it has been demonstrated that the SRM-based new pipeline has major advantages in clinical proteomics applications over traditional SRM pipelines, and it has demonstrated a dramatically improved diagnostic performance over that from antibody-based protein biomarker diagnostic methods, such as ELISA.

In selected reaction monitoring, the mass selection stage MS1 selects precursor ions that undergo fragmentation followed by product ion selection in the MS2 stage. Additional stages of selection and fragmentation can be performed.