Valery G. Voinov

Radio-Frequency-Free Cell for Electron Capture Dissociation in Tandem Mass Spectrometry

A radio frequency-free (RFF), analyzer-independent cell has been devised for electron-capture dissociation (ECD) of ions. The device is based on interleaving a series of electrostatic lenses with the periodic structure of magnetostatic lenses commonly found in a traveling wave tube. The RFF electrostatic/magnetostatic ECD cell was installed in a Finnigan TSQ700 ESI triple quadrupole (QqQ) spectrometer, and its performance was evaluated by recording product-ion spectra of doubly protonated substance P, doubly protonated gramicidin S, doubly protonated neurotensin, and triply protonated neurotensin. These spectra were readily obtained without recourse to a buffering gas or synchronizing electron injection with a specific phase of an RF field. The mass spectra produced with the modified instrument appear in all respects (other than resolution and mass accuracy, which were limited by the mass spectrometer used) to be at least as good for purposes of peptide identification as those recorded with Fourier transform ion cyclotron resonance (FT ICR) instruments; however, the effort and time to produce the mass spectra were much less than required to produce their FT ICR counterparts. The cells design and compact construction should allow it to be incorporated at relatively little cost into virtually any type of tandem mass spectrometer, for example, triple quadrupole, hybrid quadrupole ion trap, hybrid quadrupole time-of-flight, or even FT-ICR.

Exploring ECD on a Benchtop Q Exactive Orbitrap Mass Spectrometer

As the application of mass spectrometry intensifies in scope and diversity, the need for advanced instrumentation addressing a wide variety of analytical needs also increases. To this end, many modern, top-end mass spectrometers are designed or modified to include a wider range of fragmentation technologies, for example, ECD, ETD, EThcD, and UVPD. Still, the majority of instrument platforms are limited to more conventional methods, such as CID and HCD. While these latter methods have performed well, the less conventional fragmentation methods have been shown to lead to increased information in many applications including middle-down proteomics, top-down proteomics, glycoproteomics, and disulfide bond mapping. We describe the modification of the popular Q Exactive Orbitrap mass spectrometer to extend its fragmentation capabilities to include ECD. We show that this modification allows ≥85% matched ion intensity to originate from ECD fragment ion types as well as provides high sequence coverage (≥60%) of intact proteins and high fragment identification rates with ∼70% of ion signals matched. Finally, the ECD implementation promotes selective disulfide bond dissociation, facilitating the identification of disulfide-linked peptide conjugates. Collectively, this modification extends the capabilities of the Q Exactive Orbitrap mass spectrometer to a range of new applications.