Electron-impact and laser-photolytic fragmentation fluorescence spectrometry of ammonia, methylamine and acetonitrile

Analytical fluorescence spectrometry is an inherently sensitive technique, yet it is limited by the fact that many compounds do not exhibit measurable fluorescence. In this work, fluorescence spectrometry is extended to the analysis of compounds which are inherently nonfluorescent. Three nitrogen-containing compounds (ammonia, methylamine and acetonitrile) are subjected to fragmentation in the gas phase by electron-impact and laser-photolysis. Some of these fragments (both ions and neutrals) are formed in electronically excited states and thus are available to decay radiatively. Ammonia, methylamine and acetonitrile were selected for study by both electron-impact and laser-photolysis induced fragmentation fluorescence. The two methods of fragmentation and/or excitation are compared in terms of their limits of detection and linear dynamic range. Ammonia, methylamine and acetonitrile produce emissive fragments such as NH, CH, H, or CN with high efficiencies. These compounds will be used to establish benchmarks for limits of detection and linear dynamic range achievable by the electron-impact and laser-photolysis instruments in this laboratory. The careful optimization of instrumental parameters including electron beam intensity, laser power density, collection optics efficiency, optical throughput and signal-processing techniques will be performed. Among the conclusions to be discussed is the complementary nature of the electron-impact and laser-photolytic fragmentation-fluorescence methods, both to each other and to established techniques such as mass spectrometry and multi-photon ionization spectroscopy