Structural characterization of organic molecules by negative ions in laser microprobe mass spectrometry. Part 1—Neutral compounds

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Abstract
Laser microprobe mass spectrometry (LMMS) has been used to systematically study polyfunctional molecules, covering a wide range of structure and polarity. The knowledge about the mechanisms actually involved for desorption and ionization (DI) of organics by laser microbeam irradiation of solid samples at high‐power density is rather limited. Therefore we have elaborated a set of tentative hypotheses about DI in LMMS, permitting consistent rationalization of detected signals. The technique apparently combines desorption under mild conditions, shown by the release of intact thermolabiles, with extensive fragmentation. Structural data are typically distributed between cations and anions. Interpretation of negative‐ion detection mode mass spectra often represents intricate problems, partly due to the lack of sustaining background information from conventional mass spectrometry. Selected examples are presented to illustrate the occurrence of electron capture ionization, the role of heteroatoms in the formation of negative ions and the tendency to undergo complex skeletal rearrangements. Although LMMS was originally aimed at microprobe applications, it has been found to be a valuable tool in organic mass spectrometry.