Characterization of matrix effects and surface organic reactions by mass spectrometric methods
Abstract
This research has focused on two areas of interest in mass spectrometry. Beam-induced surface reactions of organic compounds are studied using secondary ion mass spectrometry (SIMS) and gas phase ion/molecule reactions are examined by mass spectrometry/mass spectrometry (MS/MS). The second field of study is the characterization of matrix effects in molecular SIMS with regard to the mechanism of desorption ionization. Molecular analysis of surfaces is an established area of application for SIMS, and interest is likely to continue at a high level. The particle beams employed in SIMS can induce surface organic reactions. Under low flux argon ion bombardment, nitryne and methyne transfer at interfaces occur in benzotriazole and benzimidazole, respectively. Methyl transfer is observed for compounds with good methyl cation donor and acceptor sites in a single molecule, for example, carnitine. A beam-induced pyrylium to pyridinium salt conversion, analogous to the solution reaction, is also demonstrated in the presence of ammonium chloride. The same process is shown to occur in the gas phase via ion/molecule reactions when amines are used as chemical ionization reagent gases. The MS/MS experiment using a triple quadrupole instrument, which establishes ionic relationship, is used to determine the reaction products. Results of a series of experiments are reported in which the matrix is varied in order to delineate its effects, and to determine how they can successfully be used in an analytical experiment. Various matrices, including ionic, acidic, and neutral molecules are employed admixed with the samples of interest in SIMS. The investigations of fragments as well as intact molecular ions and ion/molecule products are presented. Data from these various experiments are accommodated in a model for molecular emission. The processes of desorption/ionization are explored through the addition of a matrix. It is shown that surface matrix modifications are particularly useful in clarifying the sputtering mechanism. A number of ionization methods including fast atom bombardment (FAB), laser desorption (LD), electron impact (EI), and chemical ionization (CI) are utilized in this thesis to aid in elucidating the matrix effects. Comparisons are also made between SIMS and other desorption ionization methods such as FAB and LD.
Degree
Ph.D.
Advisors
Cooks, Purdue University.
Subject Area
Analytical chemistry
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.