Info

allows fingerprinting of less than 10 g of sample. However, neutral fragments are not registered by the LAMMA instrument since the minute amounts of products produced per laser shot preclude the use of further ionisation procedures. Therefore, most of the detected ions are probably photolysis products and/or intact ion-molecule complexes and due caution should be exercised in referring to these spectra as "pyrolysis mass spectra".

In principle, laser Py-MS has tremendous potential because it allows rapid direct heating of the sample while heating of large reactive substrate areas is avoided. Moreover, the high spatial resolution achieveable opens up a whole new dimension in the analysis of many different types of samples. Nevertheless, there are serious practical problems in controlling the amount of energy deposited per unit sample volume, in defining optimum parameters and in constructing suitable mass spectrometers for recording laser pyrolysis phenomena. These problems may take many more years before being adequately resolved.

A highly promising approach towards the simultaneous detection of ions from laser processes, without resorting to time-of-flight systems or photographic plates, is the development of electro-optical ion detectors using channel electron multiplier arrays in combination with vidicon or photodiode array readout systems (refs. 38, 39). This approach, however, is costly, technically complex and still in a relatively early stage of development.

0 0

Post a comment