Laser desorption (followed by electron ionization) Fourier-transform i
on cyclotron resonance (LD/EI-FTICR) mass spectra have been obtained f
or thin and thick deposits of purified C60 as well as benzene extracts
of fullerene-laden arc-welded graphite soot under identical mass spec
tral conditions. Thick (but not thin) deposits exhibit 'giant fulleren
e'-like carbon cluster-ion distributions, in either positive- or negat
ive-ion mode; giant fullerene ions observed by mass spectrometry there
fore do not necessarily prove that neutral giant fullerenes were prese
nt in the original sample, which is consistent with recent laser vapor
ization and plasma desorption mass spectrometry results. FTICR-MS of t
he residual soot remaining after benzene extraction yielded much more
abundant 'giant fullerene' ions extending above C500+, which are proba
bly derived both directly from the corresponding giant neutral carbon
clusters in the sample and by the nucleation process seen for thick de
posits of the extracts. The results shown here firmly establish the im
portance of sample thickness in the mass spectrometric examination of
fullerene soot.