Direct analysis of plant materials using ambient ionization mass spectrometry
Abstract
Ambient ionization mass spectrometry has revolutionized the area of mass spectrometric analysis by allowing the analysis of organic and inorganic compounds in their native environment without sample preparation. Eliminating sample preparation has consequently reduced analysis time by several orders of magnitude compared to traditional mass spectrometry techniques such as those involving liquid and gas chromatography. This has been true especially in the analysis of plant materials, where extensive extraction and purification steps are typically required prior to mass analysis. Here we report on applications of different ambient ionization methods developed in our laboratory for direct analysis of biologically relevant compounds in plant materials. The first part of this thesis discusses the use of the low temperature plasma (LTP) probe for qualitative analysis of extra virgin olive oil. Compounds which could be used to determine the authenticity of extra virgin olive oil such as free fatty acids and phenolic compounds were detected without the need for organic solvents or extraction processes. The second part of the thesis explores the direct analysis of chlorophyll catabolites in senescent plant tissues using desorption ionization (DESI) mass spectrometry. Non-fluorescent chlorophyll catabolites (NCCs), which are the final products of chlorophyll degradation, were detected and their molecular structures confirmed using tandem mass spectrometry (MS/MS) and reactive-DESI experiments. A novel imprinting method for imaging the spatial distribution of plant metabolites is described as well. Lastly, the relatively new paper spray ionization method was applied for direct analysis of polar lipids in green microalgae. A multi-step experimental protocol was employed to successfully characterize four classes of lipids in microalgae without the need for sample preparation. A novel approach for determining the position of unsaturation in olefins using reactive-paper spray ionization is described. Ozone produced in situ using simple low temperature plasma was used as the reagent molecule to cleave double bonds in the ions being analyzed by mass spectrometry.
Degree
Ph.D.
Advisors
Cooks, Purdue University.
Subject Area
Analytical chemistry
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