Ion/surface collision phenomena and peptide analysis in tandem mass spectrometry

Kevin Lynn Schey, Purdue University

Abstract

Low-energy polyatomic ion/surface collision phenomena and peptide sequencing are examined by tandem mass spectroscopy. Instruments constructed for these studies include: a new tandem time-of-flight instrument, an in-line ion/surface collision device, and a pentaquadrupole instrument. Fundamental aspects of ion/surface collisions are examined such as the effect of collision energy on internal energy deposition, ion/surface reactive collisions and low-energy sputtering. Internal energy deposition increases with collision energy in all instruments with approximately 10-15% of the collision energy deposited as internal energy. At low collision energies ion/surface reactions compete with dissociation of the parent ion. At collision energies above 100 eV, sputtering of surface adsorbates is the dominant process. The nature of the target is important even at a vacuum of 10$\sp{-6}$ torr, where all surfaces are expected to be unclean. Stainless steel-like targets are found to deposit more internal energy and produce more ion/surface reaction products and sputtering products than aluminum targets. Graphite targets produce only dissociation of CF$\sbsp {3}{+}$ ions when attempting to sputter surface adsorbates. An analytical approach to peptide sequencing is taken to obtain the maximum and most interpretable sequence information using both MS/MS and MS/MS/MS scan modes. More abundant fragmentation is observed using ion/surface collisions compared to gas phase collisions for several large peptides. MS/MS/MS scan modes are applied to simplify sequencing by allowing only one type of sequence ion, e.g. N-terminal ions, to be observed. The reaction intermediate scan produces the simplest spectra with no interfering ions and provides the best detection limits. The selective parent scan produces the most easily interpretable spectra, but interferences are expected in mixture analysis. The pentaquadrupole instrument produces higher quality MS/MS/MS data than a hybrid BEQQ instrument. MS/MS studies of target gas effects in collision activated dissociation in both low- and high-energy collisions show a dependence on the parent ion mass to the target mass in low-energy experiments and very little effect in high-energy experiments.

Degree

Ph.D.

Advisors

Cooks, Purdue University.

Subject Area

Analytical chemistry

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