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Eur. J. Mass Spectrom. 6, 11 - 17 (2000)

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

Jürgen H. Gross*
Organisch-Chemisches Institut, Im Neuenheimer Feld 270, 69120 Heidelberg, . E-mail:
Steffen M. Weidner
Bundesanstalt für Materialforschung und -prüfung, Unter den Eichen 87, 12205 Berlin,

ABSTRACT:
The influence of electric field strength and emitter temperature on dehydrogenation and CC cleavage in field desorption (FD) mass spectrometry of polyethylene (PE) oligomers of average molecular weights ranging from 500 to 2000 is examined. Low mass oligomers yield molecular weight (MW) distributions that are basically in accordance with results from gel-permeation chromatography. For these materials, dehydrogenation can be greatly reduced by reduction of the emitter potential. Furthermore, the influence of emitter potential on MW distributions indicates the occurrence of field-induced CC cleavages. 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. Experiments reveal that the application of FD-MS to PE oligomers is limited not only 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.

Keywords: field desorption, field ionization, polyethylene, oligomer, electric field strength, emitter potential, emitter temperature, dehydrogenation, CC cleavage, metastable ion

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