Ion activation methods for tandem mass spectrometry

Abstract

This tutorial presents the most common ion activation techniques employed in tandem mass spectrometry. In-source fragmentation and metastable ion decompositions, as well as the general theory of unimolecular dissociations of ions, are initially discussed. This is followed by tandem mass spectrometry, which implies that the activation of ions is distinct from the ionization step, and that the precursor and product ions are both characterized independently by their mass/charge ratios. In collision-induced dissociation (CID), activation of the selected ions occurs by collision(s) with neutral gas molecules in a collision cell. This experiment can be done at high (keV) collision energies, using tandem sector and time-of-flight instruments, or at low (eV range) energies, in tandem quadrupole and ion trapping instruments. It can be performed using either single or multiple collisions with a selected gas and each of these factors influences the distribution of internal energy that the activated ion will possess. While CID remains the most common ion activation technique employed in analytical laboratories today, several new methods have become increasingly useful for specific applications. More recent techniques are examined and their differences, advantages and disadvantages are described in comparison with CID. Collisional activation upon impact of precursor ions on solid surfaces, surface-induced dissociation (SID), is gaining importance as an alternative to gas targets and has been implemented in several different types of mass spectrometers. Furthermore, unique fragmentation mechanisms of multiply-charged species can be studied by electron-capture dissociation (ECD). The ECD technique has been recognized as an efficient means to study non-covalent interactions and to gain sequence information in proteomics applications. Trapping instruments, such as quadrupole ion traps and Fourier transform ion cyclotron resonance instruments, are particularly useful for the photoactivation of ions, specifically for fragmentation of precursor ions by infrared multiphoton dissociation (IRMPD). IRMPD is a non-selective activation method and usually yields rich fragmentation spectra. Lastly, blackbody infrared radiative dissociation is presented with a focus on determining activation energies and other important parameters for the characterization of fragmentation pathways. The individual methods are presented so as to facilitate the understanding of each mechanism of activation and their particular advantages and representative applications.

Electron photodetachment dissociation of DNA anions with covalently or noncovalently bound chromophores

“…Altogether, photodetachment of the DNA complexes upon chromophore excitation can be interpreted by the following mechanism: (1) ligands with sufficiently long excited-state lifetime undergo resonant two-photon excitation to reach the level of the DNA excited states, then (2) the excited-state must be coupled to the DNA excited states for photodetachment to occur. Our experiments also pave the way towards photodissociation probes of biomolecule conformation in the gas-phase by Förster A wide variety of activation methods can be used to fragment ions in tandem mass spectrometers [1]. Ion activation methods can be classified in the following way: collisions with neutrals (atoms, molecules or surfaces), collisions with ions (including proton and electron-transfer reagents), collisions with electrons, and photoactivation.…”

Photodissociation of non-covalent peptide-crown ether complexes

“…Upon UV photon absorption the intermolecular energy transfer is facilitated by the fast activation timescale of ultraviolet photodissociation (Ͻ10 ns) and by the collectively strong hydrogen bonding between the crown ether and peptide, thus allowing effective transfer of energy to the peptide moiety before disruption of the intermolecular hydrogen bonds. T he ongoing need for improved methods for characterizing biological molecules is driving efforts to develop new ion activation and dissociation approaches in mass spectrometry (MS) [1,2]. Currently, collisional-activated dissociation (CAD) remains the most popular technique used to produce diagnostic fragment ions [3,4].…”

“…T he ongoing need for improved methods for characterizing biological molecules is driving efforts to develop new ion activation and dissociation approaches in mass spectrometry (MS) [1,2]. Currently, collisional-activated dissociation (CAD) remains the most popular technique used to produce diagnostic fragment ions [3,4].…”

Design and performance of a matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometer

“…The resulting products are analyzed with a subsequent TOF mass analyzer. The second form of tandem TOF instruments is the dual TOF, or TOF/TOF [12][13][14][15]. In this kind of instrument, the precursor ions are selected in a first TOF (MS 1 ).…”