C. Basic et Ra. Yost, Collision-induced dissociation breakdown surfaces for n-alkylbenzene molecular ions in a quadrupole ion trap mass spectrometer, INT J MASS, 194(2-3), 2000, pp. 121-132
Complete collision-induced dissociation (CID) breakdown surfaces showing th
e 91(+)/92(+) ratios arising from the molecular ions (M+) of n-butylbenzene
, n-pentylbenzene, n-hexylbenzene, and n-octylbenzene have been obtained on
a quadrupole ion trap mass spectrometer (QITMS). The 91(+)/92(+) ratios ar
e plotted as a function of both resonant excitation time and voltage at a q
(z)(M+) = 0.300 and at a constant He buffer gas pressure of 1.0 x 10(-4) To
rr. (uncorrected ion gauge reading). Because the 91(+)/92(+) ratios reflect
the average internal energy of the M+ ions, the surfaces provide a complet
e map of the change in ion energy over a wide range of resonant excitation
conditions. Comparisons of the 91(+)/92(+) ratios of the n-alkylbenzenes wi
th those obtained using charge-exchange mass spectrometry (CEMS) indicate t
hat the amount of internal energy deposited upon resonant excitation varies
from similar to 1.5 eV for the M+ ion of n-butylbenzene using 100 mV excit
ation, to similar to 7.5 eV for the M+ ion of n-octylbenzene using 500 mV e
xcitation. Moreover, calculations of the amount of internal energy deposite
d, as well as the percent energy transferred (%E), are found to increase as
the size of the n-alkyl goup of the M+ ion is increased, paralleling the v
end seen for the same MT ions following low-energy CID in a triple quadrupo
le mass spectrometer (TQMS) under single-collision conditions. This trend i
n the %E as a function of the size of the n-alkyl group parallels that foun
d for the low-energy CID studies performed on a triple quadrupole mass spec
trometer and thus indicates that the mechanism of CID in the QITMS is simil
ar to that thought to occur in rf-only quadrupole collision cells. (Int J M
ass Spectrom 194 (2000) 121-132) (C) 2000 Elsevier Science B.V.