Field desorption mass spectrometry of large multiply branched saturated Hydrocarbons

Large multiply branched saturated hydrocarbons containing 67-103 carbon ato ms (molecular masses 941.8-1446.8 Da) were analyzed by field desorption mas s spectrometry (FD-MS) with a double-focusing mass spectrometer. FD-MS was found to have detection limits in the 100 fmol range. The FD mass spectra e xhibited molecular ions of astonishingly low abundance. However, the fragme nt ions formed were closely related to the proposed molecular structure, al lowing us to set up rules for straightforward structure elucidation of unkn owns. In detail, (i) dehydrogenation, (ii) alkyl losses from molecular ions and (iii) subsequent alkene losses were observed. The influence of the ele ctric field strength on dehydrogenation and C-C cleavages was examined by v ariation of the emitter potential. Additionally, ion dissociations in the i on source and in the first and second field-free regions, respectively, wer e compared to study the relative importance of field-induced and thermally induced processes. Copyright (C) 2001 John Wiley gr Sons, Ltd.