Tandem Mass Spectrometers

Tandem mass spectrometers (MS/MS or MSn) can utilize multiple rounds of mass separation and detection. Following sample ionization (by methods such as ESI, MALDI, EI, etc.), precursor ions first undergo one round of mass/charge selection (known as MS1). These are then further fragmented (through CID, photodissociation, etc.) to generate product ions (MS2) for detection. Tandem in space MS/MS are typically out by segmented hybrid mass analyzers such as triple quadrupoles (TQ) and quadrupole time of flight (QTof). Quadrupole ion trap and orbitrap type analyzers can carry out tandem in time MS and are capable of trapping ions for multiple rounds of fragmentation and detection (MSⁿ). MS/MS instruments have high detection limits and low chemical noise, allowing for both qualitative and quantitative analysis of complex compounds, including proteins and oligosaccharides. They have been particularly useful in protein sequencing and proteomic applications.