Desorption electrospray ionization (DESI) mass spectrometry: Principles instrumentation and novel applications
Abstract
Mass spectrometry has the inherent advantages of being the most specific and sensitive of the generally applicable analytical methods, however the sample has to be introduced into vacuum and often goes through a complex series of steps before and after this action. In this thesis a new method of ionization (DESI), discovered in 2004, is described; it allows the rapid in situ analysis of samples in a single step with minimal or no prior sample preparation. DESI is an ambient ionization method, which means that it allows the analysis of the sample in its native environment and does not require vacuum. Initial experiments were carried out to optimize the operational parameters of DESI, improve the instrumentation and couple it to different mass analyzers while discovering/implementing novel applications along the way. The first part of the dissertation is focused on the development, optimization and design of the DESI source. Details of the coupling of the DESI source and vacuum interface are described for a wide array of homebuilt (mini and field portable) and commercial mass spectrometers. The latter part of the thesis describes novel applications of DESI to industrial, government, security, medicinal and diagnostic problems in a chronological manner. DESI was initially applied to the in situ analysis of natural products directly from plant tissue. This study was a precursor to several tissue and biological studies currently in progress. High-throughput analysis was carried out on pharmaceutical samples at up to 3 samples/s. Explosives were analyzed from skin and clothing in trace quantities and in the presence of interferents to mimic homeland security applications. Currently biofluids and bacteria are being profiled for their lipid and metabolite content, and combined with other traditional methods (NMR, GC-MS, solvent extraction) and advanced statistical tools for diagnostic, food safety, bio-safety and medicinal applications. To summarize, the overall status of DESI as an ambient ionization method since its invention, its strengths, weaknesses, improvements and future directions are addressed.
Degree
Ph.D.
Advisors
Cooks, Purdue University.
Subject Area
Analytical chemistry
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