| This dissertation considers the use of photons as energy inputs for the desorption and or desorption/ionization of sample molecules for mass spectrometric analysis. The first chapter can be considered a primer on the subject, as it presents a variety of energy input methods, mass spectrometers, and modes of coupling the two. The next two chapters discuss small molecule detection experiments from biological tissue using a previously constructed laser desorption/chemical ionization (LD/CI) mass spectrometer. Though results were produced, the method presented several drawbacks limiting its potential for mass spectrometric imaging. Namely, analysis within the confines of the mass spectrometer vacuum system was most problematic.; To circumvent these problems, a novel laser desorption mass spectrometer interface was designed, constructed, and evaluated with the results presented in Chapter 4. The interface operates at atmospheric pressure (AP) and utilizes a laser pulse to desorb intact neutral molecules, followed by chemical ionization via reagent ions produced by a corona discharge (LD-APCI). This source employs a heated capillary AP inlet coupled to a quadrupole ion trap mass spectrometer and allows sampling under normal ambient air conditions. Chapter 5 focuses on fundamental aspects of the new method including temporal ion pulse width, laser fluence effects, and demonstrates quantitative potential.; Chapter 6 explores the ability of the LD-APCI method to desorb/ionize fragile biomolecules like peptides to determine the relative softness of the new ionization method. In comparison with atmospheric pressure-matrix-assisted laser-desorption/ionization (AP-MALDI) the method provided an ∼1400 fold increase in analyte signal for certain analytes. Next, using the technique's ability to decouple the desorption and ionization processes, we present the first direct sampling of tryptic peptides from polyacryamide gels (PAGE) using the novel LD-APCI interface in Chapter 7. These results suggest the PAGE-LD-APCI-MS technique provides several advantages that could translate into a more convenient, robust methodology for the rapid identification and characterization of proteins. In the last chapter strategies regarding the further development of the method are considered. |
