Mass Spectrometry Quiz
Questions: 16 · 10 minutes
1. What species is typically formed when electron ionization removes one electron from a neutral molecule?
An even-electron protonated molecule, [M+H]+
A negatively charged molecular ion, M−•
A positively charged radical molecular ion, M+•
A neutral excited molecule with no charge
2. What sequence best describes a typical tandem mass spectrometry experiment?
Separate neutral molecules, weigh the sample, then record absorbance
Select a precursor ion, induce fragmentation, then analyze product ions
Fragment all ions first, then select one unfragmented molecule
Detect every ion, neutralize them, then repeat the original scan
3. A compound containing one chlorine atom commonly shows molecular-ion peaks M and M+2 in approximately what intensity ratio?
About 3:1
About 1:1
About 1:2
About 9:1
4. A molecular-ion region contains two peaks separated by 2 Da with nearly equal intensity. Which element is most strongly suggested?
Bromine
Carbon
Chlorine
Sulfur
5. What does the vertical axis of a conventional mass spectrum usually show?
Exact neutral mass in daltons
Ion abundance, commonly expressed relative to the base peak
Time elapsed since sample preparation
The resolving power at each scan
6. A volatile compound gives extensive fragmentation and an extremely weak molecular ion under electron ionization. Which change would most directly help produce a more informative quasi-molecular ion while retaining a gas-phase source?
Raise the electron energy well above the usual EI setting
Lower the detector gain while keeping EI conditions unchanged
Increase the source temperature until fragmentation stops
Use a softer method such as chemical ionization
7. Which electron energy is conventionally used for standard, library-comparable electron ionization spectra?
7 eV
700 eV
70 eV
7,000 eV
8. A laboratory must distinguish two candidate molecular formulas that share a nominal mass but have different exact masses. Which measurement is most useful?
Low-resolution relative abundance alone
High-resolution accurate mass
Gas-chromatography retention time alone
The source temperature without a spectrum
9. A confirmed molecular ion appears at m/z 86, and a major fragment appears at m/z 43. What neutral mass was lost in forming that fragment, assuming both ions are singly charged?
86 Da
29 Da
43 Da
129 Da
10. What is the main function of a quadrupole mass analyzer?
To separate compounds by boiling point before ionization
To ionize molecules with a pulsed laser
To measure ion mass by magnetic deflection alone
To transmit selected m/z values using oscillating electric fields
11. In a mass spectrum, what does the horizontal axis usually represent?
Mass-to-charge ratio (m/z)
Ion intensity measured in detector counts
Chromatographic retention time
Ionization energy in electronvolts
12. In a time-of-flight analyzer, two singly charged ions receive the same kinetic energy. Which ion reaches the detector first?
The ion with the greater mass
They arrive together because their charges match
Arrival order depends only on relative abundance
The ion with the lower m/z value
13. Two ions have the same nominal mass but slightly different exact masses. Which instrument characteristic determines whether their peaks can be separated?
Scan duration
Resolving power
Detector gain
Sample injection volume
14. Which sample is generally the best candidate for direct analysis by conventional GC–EI–MS?
A volatile, thermally stable organic compound
An intact high-mass protein in aqueous buffer
A nonvolatile ionic polymer that decomposes when heated
A living cell that must remain viable after analysis
15. What is the base peak in a mass spectrum?
The peak with the lowest m/z value
The molecular-ion peak
The peak produced by background gas
The most intense peak, assigned 100% relative abundance
16. An EI molecular ion from a typical organic compound containing only carbon, hydrogen, nitrogen, and oxygen has an odd nominal mass. What does the nitrogen rule suggest?
The ion must carry two positive charges
The molecule contains no nitrogen atoms
The molecule contains an odd number of nitrogen atoms
The molecule must contain an odd number of oxygen atoms