Date of Award
Doctor of Philosophy
Robert S. Houk
This dissertation describes new applications for electrospray laser desorption ionization mass spectrometry imaging (ELDI-MSI). While ELDI was introduced over a decade ago, relatively few technical advancements or applications have been published. ELDI combines laser ablation with an ultraviolet (UV) laser with electrospray ionization (ESI). A similar method using an infrared (IR) laser known as laser ablation electrospray ionization (LAESI) operates under the same general setup as ELDI. However, the inherent shorter wavelengths used allow for ELDI to achieve higher spatial resolutions when compared with LAESI. Thus, ELDI was used on various plant samples as a comparison to studies done with LAESI, but at greater spatial resolutions than reported in those studies. The results using ELDI were shown to be comparable to LAESI.
A more extensive study on plant leaves was done to show the applicability of ELDI to study biological pathways and phenomena. Light exposure was altered across coleus leaves and the differences in concentrations of sugars, amino acids, and flavonoids were monitored over time. Using ELDI-MSI, a source-sink relationship between the two halves of each leaf was observed.
Next, the uptake of isotopically labeled glucose media was observed in Arabidopsis plants over a two-week time period. This was done at high spatial resolution (50 ÃÂµm) for an atmospheric pressure, matrix-free method. Plants grown in the isotopically labeled glucose solution were shown to have isotopically enriched amino acid signals in the mass spectra and corresponding MS-images. This showed that the glucose media directly participated in the biological pathways which make the amino acids. The localization of the glucose uptake was observed in the MS-images.
LAESI utilizing an IR laser needs appreciable water content for an ablation event to occur. However, ELDI using a UV laser does not. Therefore, ELDI can analyze “dry” samples where traditional LAESI cannot. This led to the analysis of pharmaceutical tablets with ELDI and its capability to image tablets was demonstrated. The study was the first application of either LAESI or ELDI to image tablets, and the first MSI-method to diagnose agglomeration and crystallinity in pills. This is important to the pharmaceutical industry, as crystallinity alters the bioavailability of active pharmaceutical ingredients.
Patrick Alden Mcvey
Mcvey, Patrick Alden, "Direct analysis of solid samples by electrospray laser desorption ionization mass spectrometry imaging: From plants to pharmaceuticals" (2018). Graduate Theses and Dissertations. 16636.