A second line of Py-MS studies on biomaterials which has its foundations in the late 1960's, is laser Py-MS. Here pioneering studies were reported in 1966 by Vastola and Pirone (ref. 24), who used a ruby laser in combination with a time-offlight mass spectrometer for the analysis of coal samples. Similar experiments were published by Joy et al. (ref. 25) in 1968, whereas in 1970 Karn et al. (ref. 26) described laser Py-MS of coal using an off-line pyrolysis technique with a ruby and a CO,, laser and analysing the pyrolysis products by high resolution mass spectrometry. Laser Py-MS creates yet another definition problem. During intense laser radiation, fragmentation of molecules may occur by direct bond scission due to electronic excitation (photolysis) rather than by relaxation of vibrational excitation resulting in heating of the whole molecule (pyrolysis or thermolysis). Some of the later Py-MS studies tried to avoid this ambiguity by using infrared lasers (mainly CO,, lasers) at beam intensities which precluded the occurrence of multiphoton excitation. Examples of such studies include the work of Vanderborgh and Fletcher on synthetic polymers and geopolymers (ref. 27) and the studies of Kistemaker et al. on synthetic polymers (ref. 28) and nucleic acids (ref. 29). To confuse further the issue of process definitions in laser mass spectrometry: even when using infrared lasers, spontaneous ionisation of organic molecules occurs through ion-molecule reactions between small inorganic cations or anions and neutral organic molecules (refs. 30, 31). Apart from these intact ion-molecule complexes, often referred to as "quasi-molecular ions", fragment ions can also be found, obviously formed by thermal fragmentation either before or after the ion-molecule reaction (ref. 30).
The most recent development in laser Py-MS appears to be the laser microprobe mass analyser (LAMMA) developed by Kaufmann et al. (ref. 32) and further improved by Wechsung et al. (ref. 33). Originally developed for the analysis of intracellular electrolytes and trace metal concentrations, the LAMMA system has also produced spectra exhibiting characteristic fragment patterns of polymeric organic materials (ref. 34) and cells (refs. 35, 36) as well as the above described class of ion-molecule complexes (ref. 37). The high spatial resolution (better than 0.5 urn)
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