3. Molecular Mass Spectrometry
a. What resolution would be necessary in order to resolve peaks
from univalent ions having molar masses of 1,058.0 g/mol and
1,058.5 g/mol?
b. A certain MS uses a magnetic sector mass analyzer having a
fixed accelerating voltage of 2.95 kV and a radius of 0.233 m.
What magnetic field (in T) must be used to focus a carbon dioxide
ion [CO2+] on the detector?
c. Determine the time of flight for an 800 m/z ion accelerated
across 6.5 kV and allowed to drift through a length of 2 m.
d. Naphthalene, a polyaromatic hydrocarbon
(C10H8), was analyzed by MS using chemical
ionization and a quadrupole mass analyzer. The base peak occurred
at m/z = 129, and the largest ion mass in the spectrum was seen at
m/z = 156. Explain these observations.
e. Consider the molecules X below (molecule X = A-B-B-C) as
analyzed by MS. The molecule can be described as a system with
three possible fragments: fragment A has a molecular mass of 10
amu, fragment B has a mass of 15 amu, and fragment C has a mass of
20 amu. Assume that (1) the charges generated on the fragments are
either +1 and only one bond is cleaved for each
fragmentation. List all possible ions that could be
generated, and determine if each could be distinguished explicitly
and if any ion would have m/z similar to other ions.
f. What would be the velocity of a single methyl ion
(CH3+) if it were accelerated across a
voltage of 5.0 x 10^2 volts.
g. What voltage would be needed to accelerate a
tert-butyl dication
(C4H9^2+) to a velocity of 1.0 x
10^6 m/s?
h. Calculate the resolution to resolve peaks for
CH2N (M = 28.0187) and N2+ (M =
28.0061)
i. Calculate the ratio of (M+2) to M+ peak height for
C10H6Br2.