Table 1.

Summary of MS-Based Approaches Mentioned in the Text

Acronym	Technique	Description
CID (or CAD)	Collision induced dissociation (Collisionally activated dissociation)	Technique for fragmenting ions in the gas phase, whereby ions are accelerated by an electrical potential and allowed to collide with neutral gas molecules such as argon or xenon.
ECD	Electron capture dissociation	Technique for fragmenting ions in the gas phase by causing them to interact directly with low-energy free electrons.
ESI	Electrospray ionisation	Soft ionisation technique whereby ions are produced in the gas phase by applying a voltage to the sample solution and creating an aerosol.
ETD	Electron transfer dissociation	Technique for fragmenting ions in the gas phase by transferring electrons to them from a radical anion such as anthracene or azobenzene.
FT MS	Fourier Transform based MS	Technique for determining the m/z ratio of ions through the frequency signals that the ions generate within the instrument. The mass spectrum is derived by applying a Fourier transform to the frequency data.
FT-ICR	Fourier Transform ion cyclotron resonance	Type of FT-based MS in which mass spectra are derived from the ion cyclotron resonance frequencies produced by ions as they rotate in a magnetic field.
HCD	Higher energy C-trap (or collisional) dissociation	A CID technique specific to Orbitrap instruments in which the fragmentation of gas phase ions takes place outside the orbitrap analyzer.
IM	Ion mobility	Technique used to separate molecular ions in the gas phase based on their mobility in a buffer gas under the influence of a weak electric field.
ISCID	In-source collision induced dissociation	Type of CID in which ions are fragmented in the source region of the mass spectrometer.
IRMPD	Infrared multiphoton dissociation	Technique for fragmenting ions in the gas phase by the absorption of multiple infrared photons.
MALDI	Matrix-assisted laser desorption/ionisation	Soft ionisation technique whereby macromolecules are embedded in a solid organic matrix and subsequently desorbed and ionised by a pulse of laser light.
MS/MS or MS2	Tandem MS	Method of analysis involving two stages of MS selection. The first MS stage separates sample components according to their m/z. During the second MS stage, the selected ions are subsequently subjected to fragmentation and mass spectra of the fragmentation products are obtained.
-	Orbitrap	A FT-based analyzer composed of an outer barrel-like electrode and an inner spindle-like electrode. Ions are trapped in an orbital motion around the spindle and the frequency signals that arise from the resulting image current are used to calculate the mass spectrum.
NEMS	nanoelectromechanical systems	A nanoscale device which resonates at high frequency and can function as a highly sensitive mass sensor. Instead of measuring m/z ratio, NEMS sensors register jumps in frequencies that are directly proportional to the mass of the adsorbed species.
Q	Quadrupole	An analyzer composed of four parallel metal rods to which a radio frequency voltage and direct current voltage are applied. For a given ratio of voltages, ions travelling down the quadrupole having the appropriate m/z ratio will proceed through the analyzer, while others will have unstable trajectories and collide with the rods.
TOF	Time-of-flight	An analyzer in which ions are accelerated in an electric field and then allowed to drift through a field-free region to a detector; the m/z of the ions is calculated from the time taken to reach the detector.