High pressure fluid pulsed injection in supersonic beam/mass spectrometry with resonant two photon ionization.

The sample introduction of non-volatile and thermally labile compounds is an important problem in mass spectrometry. In this thesis, supercritical fluids (CO$\sb2$, N$\sb2$O, NH$\sb3$) and subcritical fluids (H$\sb2$O, CH$\sb3$OH) have been used to introduce these samples into a time-of-flight mass spectrometer with the use of a supersonic expansion. A high pressure pulsed valve, which is capable of withstanding pressures as high as 400 atm, has been constructed in order to inject these high pressure fluids into vacuum at 10$\sp{-5}$ torr for supersonic expansions. The short pulses permit the use of a 200-330 $\mu$m orifice in order to increase the molecular beam density without overloading the moderate size pumping system. Resonant two-photon ionization could then be used to produce either molecular ions or fragmentation using UV laser radiation at different wavelengths and powers. In addition, the absorption profile observed due to the absorption of the first photon becomes narrow because of the cooling effect of the supersonic expansion, even with the use of these polyatomic carrier fluids. Relatively sharp wavelength ionization spectra ($<$0.10nm) are obtained by monitoring the molecular ion intensity as a function of the laser wavelength. These wavelength ionization spectra can then be used for distinguishing sample compounds. Several classes of compounds, such as PAH's, neuroleptic drugs, amines and small peptides, have been successfully introduced into the time-of-flight mass spectrometer by this high pressure fluid pulsed injection method with resonant two-photon ionization detection.PhDAnalytical chemistryPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/128280/2/8907123.pd