MSn Scan - Stellar MS - Stellar Mass Spectrometer Operating Manual - Software - MSn Scan - Scan Parameters - Scan Types - Stellar MS

Scans with multiple stages of mass spectrometry are often referred to as MS/MS, or MS/MS/MS, or are generalized as MSⁿ scans.

An MSⁿ scan experiment typically involves 2 to 3 stages of mass analysis (scan power of n = 2 to n = 10). Each stage of mass analysis where n > 1 includes an ion selection step. As you raise the scan power, you can obtain more structural information that can be useful in elucidation of compounds of interest, and in targeted experiments your spectra are more selective. The Stellar MS has several advanced features that make its MSⁿ capabilities extremely powerful.

In an MS/MS scan, precursor ions fragment into product ions and spectra are acquired in a “full scan” mode for a range of m/z values. Each stage of MS grants the spectrum additional selectivity, as an analyte must have a specific chemical structure to have a certain precursor m/z and dissociate to form products with certain other m/z values. Full-scan MS/MS contrasts with the SRM mode used on a triple-quadrupole instrument, where only the intensities of selected product ions are measured. Full-scan MSⁿ spectra afford additional sensitivity, selectivity and utility over triple-quadrupole based SRM, because multiple product ions are often formed with the same collision energy and are therefore accumulated in parallel instead of serially as in a triple-quadrupole, and product ions can be selected for monitoring in post-processing instead of pre-experiment.

The following steps occur during an MSⁿ experiment:

1. In the first stage of mass analysis, the quadrupole mass analyzer isolates the precursor ions.
2. In the first ion activation stage, one of the following occurs:
3. - The selected precursor ions are introduced into the ICRM at high energy and are fragmented, i.e. HCD activation is employed.
4. - The selected precursor ions are introduced into the ICRM at low energy, stored, then transferred to the high-pressure cell where they are trapped, cooled, and resonantly excited, i.e. resonance CID activation is employed.
3. In the second stage of mass analysis, the ions are transferred to the low-pressure cell for resonance ejection mass analysis, whereby ions are ejected out of slots in the rods to the external ion detector.

For MSⁿ, where n > 2, additional ion activation stages (HCD or CID) are coupled with broadband waveform based ion isolation as an intermediate mass analysis step. Unlike the traditional quadrupole mass filter selection performed in the first mass analysis stage, ion trap based precursor selection can simultaneously select more than one precursor, which can make MSⁿ much more sensitive.