The analysis of nonfluorescent compounds by electron impact-and laser photolysis-fragmentation fluorescence spectrometry

The development of alternative, fluorescence-based analytical techniques is being driven by two important properties of conventional fluorometric techniques; one, the characteristically low limits of detection obtainable for intensely fluorescent compounds and, two, the relatively small number of compounds possessing high quantum yields for fluorescence.

Small molecules, e.g., diatomics, triatomics, and atoms, are known to be intensely luminescent. Fragmentation Fluorescence Spectrometry (FFS) is a technique that takes advantage of this property and the fact that virtually any organic or organometallic compound can be broken into small molecular fragments. In the work presented in this dissertation, fragmentation of gas-phase molecules is accomplished through either the absorption of photons by laser photolysis (LP) or electron-impact bombardment (El). The fluorescence is measured directly and related to the original amount of the parent compound.

In the following document, quantitative analyses (limits of detection, linear dynamic range, and precision) were carried out on a number of individual compounds by both El- and LP-FFS. The detection limits of ammonia by El- and LP-FFS were 20 pmol and 3.4 pmol, respectively. The compounds methylamine and acetonitrile were also analyzed using both techniques, with detection limits by El of 0.3 nmol and 0.1 nmol, respectively, and by LP, 15 pmol, for methylamine. Acetonitrile did not produce fluorescent fragments under these IV V conditions of laser photolysis. Linear behavior was typical (2-3 decades) with the exception of ammonia in LP-FFS. Measurements made by EI-FFS are more reproducible than those of LP-FFS. Analytical precision as expressed by percent relative standard deviation was typically <1.5% for El- and -6% for LP-FFS.

The analysis of a series of aliphatic amines by LP-FFS indicated that detection limits do not dramatically increase for amines of higher molecular weights.

Studies of the use of a second laser with LP-FFS in a "photolysis-probe" arrangement to excite additional fluorescence from molecular fragments are described. No enhancement of fragment fluorescence was observed under the experimental conditions of this study.