Study of the mechanism of direct laser desorption/ionisation for some small organic molecules (M < 400 Daltons)

Abstract

Aspects of direct laser desorption/ionisation have been studied for three molecules, aminotriazole (positive ion), dinoterb and ioxynil (negative ion). The samples are deposited on metallic substrates, and a nitrogen laser is used for desorption/ionisation; ion yields are measured with a time-of-flight mass spectrometer. Previous work had shown that ion yields can strongly vary from one substrate to another, and that this variation does not reflect the (calculated) metal surface temperatures. New results obtained in this work indicate that the desorption/ionisation mechanism is linked to the physical state of the substrate surface. Copyright 1999 John Wiley & Sons, Ltd.

Direct Protein Detection from Biological Media through Electrospray-Assisted Laser Desorption Ionization/Mass Spectrometry

“…Laser desorption (LD) allows sampling over a small and defined area and, therefore, guarantees high spatial resolution of a solid sample. Unfortunately, only relatively small biological and chemical compounds (e.g., <3000 Da) can be detected through direct LD/MS analyses. − The failure to detect the signals of ions of larger molecules, such as proteins, after LD may be due to their low ionization efficiencies, their decomposition induced by the laser energy, or their rapid neutralization during the desorption/ionization processes. It has been reported, however, that a larger number of neutral molecules are produced during a laser desorption event, and consequently, several different approaches have been applied to post-ionize these neutral organic species. − Unfortunately, again, only small compounds are ionized and detected when using these approaches.…”