Using electron induced dissociation (EID) on an LC time-scale to characterize a mixture of analogous small organic molecules

Liquid Extraction Surface Analysis (LESA) Electron-Induced Dissociation and Collision-Induced Dissociation Mass Spectrometry of Small Molecule Drug Compounds

Here, we present liquid extraction surface analysis (LESA) coupled with electron-induced dissociation (EID) mass spectrometry in a Fourier-transform ion cyclotron resonance mass spectrometer for the analysis of small organic pharmaceutical compounds directly from dosed tissue. First, the direct infusion electrospray ionisation EID and collision-induced dissociation (CID) behaviour of erlotinib, moxifloxacin, clozapine and olanzapine standards were compared. EID mass spectra were also compared with experimental or reference electron impact ionisation mass spectra. The results show that (with the exception of erlotinib) EID and CID result in complementary fragment ions. Subsequently, we performed LESA EID MS/MS and LESA CID MS/MS on singly charged ions of moxifloxacin and erlotinib extracted from a thin tissue section of rat kidney from a cassette-dosed animal. Both techniques provided structural information, with the majority of peaks observed for the drug standards also observed for the tissue-extracted species. Overall, these results demonstrate the feasibility of LESA EID MS/MS of drug compounds from dosed tissue and extend the number of molecular structures for which EID behaviour has been determined. Graphical Abstract ᅟ.

Electron-ion reaction-based dissociation: A powerful ion activation method for the elucidation of natural product structures

The structural elucidation of natural products (NPs) remains a challenge due to their structurally diversities and unpredictable functionalities, motifs, and scaffolds. Tandem mass spectrometry (MS/MS) is an effective method that assists the full elucidation of complicated NP structures. Ion activation methods play a key role in determining the fragmentation pathways and the structural information obtained from MS/MS. Electron-ion reaction-based dissociation (ExD) methods, including electron capture dissociation (ECD), electron transfer dissociation (ETD), electron-induced dissociation (EID), and electron detachment dissociation (EDD), can induce the breakage of specific chemical bonds and the generation of distinct fragment ions. This review article provides an overview of the mechanisms, instrumentation, and typical applications related to ExD MS/MS in the structural elucidation of NPs, primarly including lipids, oligosaccharides, glycoconjugates, metabolites, and pharmaceutical drugs. This work aims to reveal the capacity and potential of ExD mass spectrometry in analyzing NPs and consequently helping the NP communities to utilize the modern capabilities of MS/MS in the discovery and evaluation of novel NPs.

Electron-based fragmentation methods in mass spectrometry: An overview

Tandem mass spectrometry (MS/MS) provides detailed information for structural characterization of biomolecules. The combination of electron capture dissociation (ECD) techniques with Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) often provides unique ion-electron reactions and fragmentation channels in MS/MS. ECD is often a complimentary, sometimes even a superior tool to conventional MS/MS techniques. This article is aimed at providing a short overview of ECD-based fragmentation techniques (ExD) and optimization of ECD experiments for FTICR mass analyzers. Most importantly, it is meant to pique the interest of potential users for this exciting research field. © 2015 Wiley Periodicals, Inc. Mass Spec Rev 36:4-15, 2017.

Characterisation of phosphorylated nucleotides by collisional and electron-based tandem mass spectrometry

RATIONALE

Tandem mass spectrometry of phosphorylated ions can often yield a limited number of product ions owing to the labile nature of phosphate groups. Developing techniques to improve dissociation for this type of ion has implications for the structural characterisation of many different phosphorylated ions, such as those from nucleotides, pharmaceutical compounds, peptides and polymers.

METHODS

Solutions of adenosine monophosphate, diphosphate and triphosphate (AMP, ADP and ATP) were studied in a hybrid linear ion trap-Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. Precursor ions with an overall single positive charge, including protonated nucleotides or nucleotide cations containing one, two or three sodium atoms, were isolated for tandem mass spectrometry. Collision-induced dissociation (CID) was performed in the linear ion trap, with electron-induced dissociation (EID) being conducted in the FTICR cell.

RESULTS

EID resulted in many product ions not seen in CID. EID product ion spectra were seen to vary for AMP, ADP and ATP when the nucleotide cation contained zero, one, two or three sodiums. Precursor cations that contain two or three sodiums mainly formed product ions derived from the phosphate group. Conversely, when a precursor ion containing no sodium underwent EID, product ions mainly relating to the non-phosphate end of the ion were observed. The number of phosphate groups was not seen to greatly affect either CID or EID product ion spectra.

CONCLUSIONS

The presence of sodium in a precursor ion directs electron-induced bond dissociation, thus enabling targeted, and therefore tuneable, fragmentation of groups within that precursor ion. For all precursor ions, the most useful product ion spectra were obtained by EID for a precursor ion containing one sodium, with bond dissociation occurring across the entire nucleotide cation. The findings of this study can be used to improve the structural elucidation of many phosphorylated molecules by broadening the range of product ions achievable. © 2016 The Authors. Rapid Communications in Mass Spectrometry Published by John Wiley & Sons Ltd.

Structural analysis of small to medium-sized molecules by mass spectrometry after electron-ion fragmentation (ExD) reactions

Electron capture dissociation (ECD) is a tandem mass spectrometry (MS/MS) method that utilizes the interaction of ions and electrons. Its unique ability to preserve labile bonds distinguishes it from conventional threshold-based MS/MS methods, the most important of which is collision-induced dissociation (CID). During the last decade, ECD has opened up several new venues in protein analyses, for example top-down sequencing, identification of post-translational modifications, and characterization of protein-protein interactions. In recent years, a number of related dissociation techniques, so-called ExD techniques, particularly electron transfer dissociation (ETD), electron detachment dissociation (EDD), electron induced dissociation (EID), and negative electron transfer dissociation (NETD), have emerged and have extended the application range of ion-electron dissociations further. Importantly, ExD techniques have been applied beyond protein analyses, which is the focus of the current paper. This short introduction describes the application of ExD to small and medium-sized molecules and reviews important applications to natural products, biomedical compounds, synthetic molecules, crude oils, and environmental toxins.

Electron-induced dissociation (EID) for structure characterization of glycerophosphatidylcholine: determination of double-bond positions and localization of acyl chains

Glycerophospholipids are a highly abundant and diverse collection of biologically relevant lipids, and distinction between isomeric and isobaric species is a fundamental aspect for confident identification. The ability to confidently assign a unique structure to a glycerophospholipid of interest is dependent on determining the number and location of the points of unsaturation and assignment of acyl chain position. The use of high-energy electrons (>20 eV) to induce gas-phase dissociation of intact precursor ions results in diagnostic product ions for localizing double-bond positions and determining acyl chain assignment. We describe a high-resolution, tandem mass spectrometry method for structure characterization of glycerophospholipids using electron-induced dissociation (EID). Furthermore, the inclusion of nomenclature to systematically assign bond cleavage sites with acyl chain position and double-bond location enables a uniform platform for lipid identification. The EID methodology detailed here combines novel application of an electron-based dissociation technique with high-resolution mass spectrometry that facilitates a new experimental approach for lipid biomarker discovery and validation.

Electron-induced dissociation of peptides in a triple quadrupole mass spectrometer retrofitted with an electromagnetostatic cell

Dissociation of peptides induced by interaction with (free) electrons (electron-induced dissociation, EID) at electron energies ranging from near 0 to >30 eV was carried out using a radio-frequency-free electromagnetostatic (EMS) cell retrofitted into a triple quadrupole mass spectrometer. The product-ion mass spectra exhibited EID originating from electronically excited even-electron precursor ions, reduced radical cations formed by capture of low-energy electrons, and oxidized radical cations produced by interaction with high-energy electrons. The spectra demonstrate, within the limits of the triple quadrupole's resolving power, that high-energy EID product-ion spectra produced with an EMS cell exhibit essentially the same qualitative structural information, i.e., amino acid side-chain (SC) losses and backbone cleavages, as observed in high-energy EID spectra produced with a Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometer. The levels of fragmentation efficiency evident in the product-ion spectra recorded in this study, as was the case for those recorded in earlier studies with FT ICR mass spectrometers, is currently at the margin of analytical utility. Given that this shortcoming can be remedied, EMS cells incorporated into QqQ or QqTOF mass spectrometers could make tandem high-energy EID mass spectrometry more widely accessible for analysis of peptides, small singly charged molecules, pharmaceuticals, and clinical samples.