Implementation of an In-line Surface-induced Dissociation Device in a Quadrupole Time-of-flight Instrument and Its Performance

Abstract

The focus of this dissertation is the introduction of surface-induced dissociation (SID) into a commercially available quadrupole time-of-flight mass spectrometer as an alternative ion fragmentation method. The performance of the SID device was characterized and its applications were demonstrated by dissociating peptides, proteins, inorganic salt clusters and non-covalent protein complexes. The SID setup allowed direct comparison of SID with conventional collision-induced dissociation (CID) on the same instrument, taking advantage of the characteristics of Q-TOF instrumentation, including extended mass range, high sensitivity and resolution. With the SID setup installed, no significant reduction of the ion transmission was evident. SID fragmentation patterns of peptides are, in general, similar to CID, with slight differences in the relative intensities of immonium ions, backbone cleavage b- versus y- type ions, and y- versus y-NH3 ions. This suggests enhanced accessibility to high energy/secondary fragmentation channels with SID. SID studies on cesium iodide clusters (CsI) also revealed that SID deposits more internal energy.The utility of mass spectrometric methods to probe the gas phase cyclization process was studied with [D-Ala2]-Leucine Enkephalin amide. This peptide showed prominent formation of the [M-NH3]+ ion which is believed to be the linear b5 ion with a C-terminal oxazolone structure. Other fragments in the spectra indicate that the linear b5 ion undergoes cyclization, subsequent ring opening and further dissociation to rearranged fragments that cannot be explained by the initial sequence. The similarities between the cyclic and b5-ion from the linear peptide indicated the formation of a heterogeneous ion population and this is further supported by gas-phase H/D exchange experiments. An ion funnel interface to improve ion transmission at high pressures was tested in a custom built quadrupole-surface-quadrupole instrument. The ion transmission efficiency for selected bio-molecules such as YGGFLR, insulin chain-B, ubiquitin and cytochrome c showed to approach almost 90%, with the funnel interface installed. The ion transmission efficiency was effected by several factors including: the size of the analyte, the DC gradient, the RF frequency, and the RF amplitude. The higher fragmentation efficiencies for SID in the presence of the funnel interface indicated higher internal energy deposition for the funnel interface.