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 cell's 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.