Combined infrared multiphoton dissociation and electron capture dissociation with a hollow electron beam in Fourier transform ion cyclotron resonance mass spectrometry

An electron injection system based on an indirectly heated ring-shaped dispenser cathode was developed and installed in a 7 T Fourier transform ICR (FTICR) mass spectrometer. This new hardware design allows high-rate electron capture dissocn. (ECD) to be carried out by a hollow electron beam coaxial with the ICR trap. IR multiphoton dissocn. (IRMPD) can also be performed with an on-axis IR-laser beam passing through a hole at the center of the dispenser cathode. Electron and photon irradn. times of the order of 100 ms are required for efficient ECD and IRMPD, resp. As ECD and IRMPD generate fragments of different types (mostly c, z and b, y, resp.), complementary structural information that improves the characterization of peptides and proteins by FTICR mass spectrometry can be obtained. The developed technique enables the consecutive or simultaneous use of the ECD and IRMPD methods within a single FTICR exptl. sequence and on the same ensemble of trapped ions in multistage tandem (MS/MS/MS or MSn) mass spectrometry. Flexible changing between ECD and IRMPD should present advantages for the anal. of protein digests sepd. by liq. chromatog. prior to FTICRMS. Also, ion activation by either electron or laser irradn. prior to, as well as after, dissocn. by IRMPD or ECD increases the efficiency of ion fragmentation, including the w-type fragment ion formation, and improves sequencing of peptides with multiple disulfide bridges. The developed instrumental configuration is essential for combined ECD and IRMPD on FTICR mass spectrometers with limited access into the ICR trap. [on SciFinder (R)]