Pb. Oconnor et al., ISOTOPIC ASSIGNMENT IN LARGE-MOLECULE MASS-SPECTRA BY FRAGMENTATION OF A SELECTED ISOTOPIC PEAK, Analytical chemistry, 68(3), 1996, pp. 542-545
For large (>5 kDa) ionic species, Fourier transform ion cyclotron reso
nance instruments yield by far the highest mass accuracy. However, thi
s can be compromised by misassignment of the isotopic content based on
predicted natural abundances of the isotopic peaks. As an alternative
method independent of natural abundance variations, high-resolution i
solation and dissociation of a single isotopic peak yields a distribut
ion of isotopic peak abundances characteristic of the isotopic content
of the precursor peak. Accuracy is enhanced if the precursor peak is
abundant and of minimum heavy isotope content, and if the product spec
ies is abundant and of intermediate mass. In addition, such spectra of
the highest mass products are useful for identifying complementary pr
oduct pairs, a key step in sequencing proteins and nucleotides.