In-source decay and pseudo tandem mass spectrometry fragmentation processes of entire high mass proteins on a hybrid vacuum matrix-assisted laser desorption ionization-quadrupole ion-trap time-of-flight mass spectrometer.

In-source decay (ISD), although a process known for decades in mass spectrometry, has a renewed interest due to increased theoretical knowledge in fragmentation processes of large biomolecules coupled with technological improvements. We report here an original method consisting of isolating matrix-assisted laser desorption ionization (MALDI)-generated in-source fragments of large proteins and subsequently performing selective fragmentation experiments (up to four cycles) using a hybrid MALDI quadrupole ion-trap time-of-flight mass spectrometer (MALDI-QIT-TOF). This technology takes advantage of keeping high resolution on the selection of precursors and detection of fragments. It allows exhaustive N- and C-terminal sequencing of proteins. In this work, human serum albumin (HSA), β-casein, and recombinant Tau proteins were submitted to in source decay in the MALDI source. The fragments were stored in the ion-trap and submitted to sequential collision-induced dissociation (CID). Finally, ISD and pseudo MSn w...