Tandem mass spectrometry (MS/MS) is an analytical technique used in the field of mass spectrometry to identify and characterize molecules. This includes two successive mass spectrometry steps that provide improved sensitivity, selectivity, and structural information over conventional mass spectrometry.
The fundamental principle of tandem mass spectrometry involves a combination of two mass spectrometry steps: precursor ion selection and production ion analysis.
A step-by-step analysis of the process follows.
Select a precursor ion
In the first step of tandem mass spectrometry, the mass spectrometer (typically quadrupole or ion trap) selects a specific precursor ion from the ion mixture. Precursor ions are typically generated by ionization techniques such as electrospray ionization (ESI) or matrix auxiliary laser desorption/ionization (MALDI).
Afterwards, when a precursor ion is selected, it goes through a process called activation. Activation can be accomplished by collision-influenced dispatch (CID), electron capture dispatch (ECD), electron transfer dispatch (ETD), or other techniques. Activation applies energy to precursor ions, which fragment into smaller generative ions while retaining some structural information.
Collision-Induced Disociation (CID): CID is the most widely used technique in tandem mass spectrometry. This involves precursor ions colliding with gas molecules and fragmenting them.
Electron capture dissociation (ECD): ECD captures low-energy electrons by precursor ions, causing fragmentation. ECD is particularly useful for the study of peptides and proteins.
Electron Transfer Disociation (ETD): ETD transfers electrons from radical anions to precursor ions, causing fragmentation. ETD is useful for the analysis of larger biomolecules.
Higher-Energy Collateral Disociation (HCD): HCD is fragmented by exposure of precursor ions to higher energy collisions. HCD is commonly used in Orbitrap mass spectrometers.
Product Ion Analysis
In the second step, the mass spectrometer measures the mass-to-charge ratio (m/z) of the production produced in the fragmentation of the precursor ions. Generated ions are isolated and detected based on the m/z value. This step provides information on the mass and abundance of the fragment ions.
Tandem mass spectrometry is widely used in a variety of fields, including proteomics, metabolomics, constraint analysis, and environmental analysis. This allows researchers to study biological processes by identifying unknown compounds, revealing the structure of complex molecules, and analyzing the fragmentation patterns of molecules.
Proteomics
Tandem mass spectrometry revolutionized the field of proteomics by enabling large-scale identification and characterization of proteins. This is commonly used in shotgun proteomics where proteins are digested into peptides by enzymes, and the resulting peptide mixture is analyzed using tandem mass spectrometry. Fragmentation patterns of peptides provide useful information for protein identification, post-translation strain analysis, and protein quantification.
quantitative analysis
Tandem mass spectrometry is used for quantitative analysis as well as identification and structural analysis. Technologies such as Selected Reaction Monitoring (SRM) or Multiple Reaction Monitoring (MRM) can be used to monitor ion transitions from specific precursors to products to perform targeted quantification of specific molecules.
This technique has enabled significant advances in biomolecular identification such as proteins and peptides by providing sequence information and is useful for drug discovery and development. This is because it can help identify drug metabolites, study drug-target interactions, and analyze impurity properties of drugs.
Overall, tandem mass spectrometry is a versatile method that plays an important role in many scientific and industrial applications.
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