Influence of electric field strength and emitter temperature on dehydrogenation and C-C cleavage in field desorption mass spectrometry of polyethylene oligomers

The influence of electric field strength and emitter temperature on dehydro genation and C-C cleavage in field desorption (FD) mass spectrometry of pol yethylene (PE) oligomers of average molecular weights ranging from 500 to 2 000 is examined. Low mass oligomers yield molecular weight (MW) distributio ns that are basically in accordance with results from gel-permeation chroma tography. For these materials, dehydrogenation can be greatly reduced by re duction of the emitter potential. Furthermore, the influence of emitter pot ential on MW distributions indicates the occurrence of field-induced C-C cl eavages. Reliable MW distributions are more difficult to obtain from higher mass oligomers by FD-MS because of the need for higher field strength and higher emitter temperatures to effect their desorption/ionization. Experime nts reveal that the application of FD-MS to PE oligomers is limited not onl y by field-induced but also by thermally-induced fragmentations. Even then, FD mass spectra contain valuable information on mass range and homogeneity of PE samples up to about m/z 3600.