Harris QCA 8e Chapter 21
1 The resolving power (R) of a mass spectrometer is computed by dividing the mass of
the 1st peak of two adjacent peaks by the mass difference between the two peaks. If a
mass spectrometer were to resolve N2+ (mass = 28.0061 Dalton) and CO+ (mass =
27.9949 Dalton), the resolving power would be
(a) 2,500.
(b) 4.00 x 10-4.
(c) 0.9996.
2 The mass spectra of a compound containing nitrogen had an M+· nominal mass of 93.
This means that
(a) the compound contains an even number of nitrogens.
(b) the compound contains an odd number of nitrogens.
(c) the compound contains an even number of nitrogens and an odd number of chlorines.
3 In the mass spectra of a compound containing only carbon and hydrogen, the most
intense peak was found at m/z = 78. This peak is designated at the M+·peak. The M + 1
peak was determined to be 13% of the M+ peak. Using the information below, how many
carbon atoms should be contained in the compound?
Element X + 1
H 0.012n
C 1.08n
N 0.369n
(a) 6 carbons atoms
(b) 12 carbons atoms
(c) 18 carbon atoms
4 If the composition of a molecular ion is known, and you wish to propose a structure for
the molecular ion, the number of rings + double bonds may be calculated. A compound
with a composition C8H8NBrCl contains how many double bonds and rings? (revise
organic)
(a) 4.5
(b) 4
(c) 5
5 With electron ionization of the sample in a mass spectrometer, the sample will fragment
into pieces which are recorded by the detector. Some fragments are more probable than
others. Which of the following fragments is least likely to be found in a mass spectra?
(a) ·CH2
(b) ·CH3
(c) ·C3H9
6 The nominal mass of a molecule or ion is
(a) the weighted average of the masses of the isotopes of an element.
(b) the sum of atomic masses listed in the periodic table.
(c) the integer mass of the species with the most abundant isotope of each of the
constituent atoms.
7 Which of the following best describes a magnetic sector mass spectrometer?
(a) The instrument uses a magnetic field, the strength of which may be changed to allow
ions of a selected m/z ratio to pass from the source to the detector.
(b) The instrument uses four parallel metal rods to which are applied varied voltages and
a radio frequency, to separate ions ofm/z units.
(c) The instrument accelerates ions into a drift region.
8 The difference between chemical ionization and electron ionization is
(a) chemical ionization produces more fragmentation of the molecules and thus makes the
spectra easier to interpret.
(b) Chemical ionization yields less fragmentation than electron ionization.
(c) Chemical ionization involves accelerating electrons to interact with incoming
molecules while electron ionization uses an ionized reagent gas to produce m/z units.
9 The mass spectra shown below was generated by analyzing a peak emerging from a gas
chromatograph at 13.54 minutes. The top set of points was the actual data recorded, the
bottom set of data was taken from the spectrum library as a match for this compound.
Which of the following choices is the best choice for the identification of this compound?
(a) C16H34
(b) C18H38
(c) C20H42
10 The mass spectra shown below was generated by analyzing a peak emerging from a
gas chromatograph at 13.84 minutes. The top set of points was the actual recorded data.
The bottom set of data was taken from the spectrum library as a match for this
compound. Look carefully at the mass to charge peaks present. A common small
molecule fragment produced by the electron ionization of the compound is
(a) C2H4.
(b) C2H6.
(c) C3H8.
11 The time-of-flight instrument is
(a) not capable of high acquisition rates and has a nearly unlimited upper-mass range.
(b) capable of high acquisition rates with a limited upper-mass range.
c) capable of high acquisition rates and has a nearly unlimited upper-mass range.
12 Mass spectrometry has long been used to
(a) measure isotopes and decipher organic structures.
(b) measure isotopes and decipher inorganic structures.
(c) measure gases and decipher inorganic structures.
13 The most intense peak in a mass spectrum is called
(a) the mass spectrum.
(b) the mass-to-charge ratio.
(c) the base peak.
14 Which is a detector of choice for gas chromatography?
(a) transmission quadruple mass spectrometer
(b) magnetic sector mass spectrometer
(c) double-focusing mass spectrometer
15 The main limitation on resolving power of a time-of-flight mass spectrometer is
(a) that all ions emerge from the source with the same kinetic energy.
(b) that all ions do not emerge from the source with different kinetic energy.
(c) that all ions do not emerge from the source with the same kinetic energy.