Tandem time-of-flight mass spectrometry incorporating quadratic-field technology
The study involved the desig~ constructio~ optimisation and utilisation of a novel tandem time-of-flight (TOF-TOF) instrument. The instrument was designed to use a laser ion source capable of laser desorption or matrix-assisted laser desorption/ionisation. The instrument used a twin ion mirror geometry in which the first ion mirror was a single-stage ion mirror, while the second ion mirror was a quadratic-field ion mirror. The instrument was designed for highenergy (>10keV) collision-induced dissociation (CID). The initial design criteria of a tandem time-of-flight spectrometer are discussed. The design and construction of the vacuum chamber and pumping system are discussed. The design and construction of the laser ion source are covered in detail. Computer simulations of typical ion trajectories were calculated using the SIMION program. The design and construction of the steering optics, single-stage ion mirror and pulsed mass gate are discussed. Computer simulations of ion trajectories were used to characterise the ion optical properties of the system. Experiments to characterise the energy focusing properties and transmission of the single-stage ion mirror were conducted. The mass resolving power of the single-stage ion mirror were characterised. The single-stage ion mirror achieved a resolution of2000 full-width half-maximum (FWHM). The design and construction of the differentially pumped collision-cell and the quadratic-field ion mirror are outlined. Experiments to demonstrate the transmission of the collision-cell and quadratic-field ion mirror are discussed. Experiments to characterise the energy focusing properties of the quadratic-field ion mirror were conducted. The full instrument achieved precursor mass resolving powers of approximately 7000 (FWHM) for laser desorbed species and 3500 (FWHM) for MALDI generated peptide species. Initial CID results are presented. The study thoroughly discusses the problems with the current instrument configuration and goes on to propose solutions to the problems encountered.