SRM (Selected Reaction Monitoring) is a mass spectrometry technique that is mainly used for the quantitative analysis of target proteins or peptides. SRM is typically performed using a triple quadrupole mass spectrometer and is a highly sensitive and specific technique.
Here are some of the basic principles and steps for SRM-targeted proteomics assays:
1. Target selection: Before the experiment begins, you first need to select the target protein or peptide you want to measure.
2. Peptide selection: In order to detect proteins, representative peptides (often referred to as "peptide maps" or "signature peptides") are usually selected for quantification.
3. Conversion to predetermined ions: The sample is ionized in the mass spectrometer and a precursor ion is selected in the first quadrupole.
4. Fragmentation: The selected precursor ions collide with the inert gas in the colliding cell to produce fragment ions.
5. Detection of specific fragment ions: In the second quadrupole, specific fragment ions are selected and detected. This step provides a high degree of specificity for SRM.
6. Quantitation: By measuring the intensity of specific ions of specific peptides, the abundance of the target protein in the sample can be quantified.
Due to the high specificity and sensitivity of SRM, it has become an important tool in clinical research and biomarker validation. Compared to traditional non-targeted mass spectrometry proteomics techniques, SRM provides higher quantitative accuracy, especially in the case of low-abundance proteins.