Fragmentation pattern and interpretation in mass spectrometry MCQs With Answer

Fragmentation pattern and interpretation in mass spectrometry MCQs With Answer

by

Fragmentation pattern and interpretation in mass spectrometry MCQs With Answer

Understanding fragmentation patterns and interpretation in mass spectrometry is vital for B.Pharm students involved in drug analysis, structural elucidation, and quality control. This topic covers mass spectra terminology (molecular ion, base peak, fragment ions), common fragmentation pathways (alpha-cleavage, McLafferty rearrangement, neutral losses like H2O/CO/NH3), isotopic patterns (Cl, Br), tandem MS (MS/MS), collision-induced dissociation, and use of accurate mass for elemental composition. Mastering these concepts helps identify metabolites, impurities, and degradation products in GC-MS and LC-MS data. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What does a fragmentation pattern in mass spectrometry represent?

  • A sequence of chromatographic peaks over time
  • A set of fragment ions and their relative abundances produced from an ionized molecule
  • The UV-Visible absorption spectrum of a compound
  • The X-ray diffraction pattern of a crystalline drug

Correct Answer: A set of fragment ions and their relative abundances produced from an ionized molecule

Q2. Which peak is defined as the base peak in a mass spectrum?

  • The peak corresponding to the molecular ion (M·+)
  • The tallest peak given relative intensity 100%
  • The peak at the lowest m/z value
  • The first peak observed in time-of-flight MS

Correct Answer: The tallest peak given relative intensity 100%

Q3. What is the molecular ion (M·+) in electron ionization (EI) mass spectra?

  • A protonated molecule [M+H]+ commonly seen in ESI
  • The radical cation formed by removal of an electron from the neutral molecule
  • A fragment produced by alpha-cleavage only
  • An adduct formed with sodium

Correct Answer: The radical cation formed by removal of an electron from the neutral molecule

Q4. Which fragmentation process involves transfer of a hydrogen followed by cleavage resulting in a neutral fragment loss of a small molecule like ethylene?

  • Alpha-cleavage
  • McLafferty rearrangement
  • Retro-Diels–Alder reaction
  • Electron capture dissociation

Correct Answer: McLafferty rearrangement

Q5. Which functional group commonly shows prominent loss of H2O in mass spectra?

  • Alkyl halides
  • Alcohols and carboxylic acids
  • Aromatic nitro compounds
  • Perfluorinated compounds

Correct Answer: Alcohols and carboxylic acids

Q6. What is alpha-cleavage in mass spectrometry?

  • Cleavage two bonds away from a substituent causing loss of CO2
  • Cleavage adjacent to a heteroatom resulting in stabilized cation or radical
  • Fragmentation via rearrangement of a ring system only
  • Formation of adducts with alkali metals

Correct Answer: Cleavage adjacent to a heteroatom resulting in stabilized cation or radical

Q7. Which isotopic pattern indicates the presence of a single chlorine atom in a molecule?

  • M and M+1 peaks only, no M+2
  • M and M+2 peaks with ~1:1 intensity ratio
  • M and M+2 peaks with ~3:1 intensity ratio
  • A unique M+3 peak only

Correct Answer: M and M+2 peaks with ~3:1 intensity ratio

Q8. A brominated compound typically shows which isotope peak pattern?

  • M and M+1 in 1:1 ratio
  • M and M+2 in roughly 1:1 ratio
  • Only a single molecular ion peak
  • Intense M+3 peak due to 81Br and 79Br

Correct Answer: M and M+2 in roughly 1:1 ratio

Q9. In tandem MS (MS/MS), what is a common purpose of performing collision-induced dissociation (CID)?

  • Ionization of neutral molecules
  • Reducing sample matrix effects in chromatography
  • Fragmenting selected precursor ions to get structural information
  • Measuring isotopic abundances only

Correct Answer: Fragmenting selected precursor ions to get structural information

Q10. Which statement describes the even-electron rule?

  • Even-electron ions generally fragment to give odd-electron species only
  • Even-electron ions tend to produce even-electron fragments (no radical cations) under soft ionization
  • Only odd-electron ions are observed in electrospray ionization
  • It predicts isotopic distributions for halogens

Correct Answer: Even-electron ions tend to produce even-electron fragments (no radical cations) under soft ionization

Q11. Which neutral loss of 17 Da is commonly observed and diagnostic in many spectra?

  • Loss of CO
  • Loss of NH3
  • Loss of H2O
  • Loss of CH4

Correct Answer: Loss of NH3

Q12. Accurate mass measurements help determine:

  • The retention time of a compound in LC
  • The exact elemental composition (sum formula) of an ion
  • Only fragmentation pathways qualitatively
  • The UV absorbance maxima

Correct Answer: The exact elemental composition (sum formula) of an ion

Q13. Which fragment is typical for an ester under EI showing McLafferty-like cleavage?

  • A vinyl cation only
  • Loss of an alkene giving an acylium ion (RCO+)
  • Only radical neutral losses without charged fragments
  • Formation of stable protonated molecules only

Correct Answer: Loss of an alkene giving an acylium ion (RCO+)

Q14. The m/z value in mass spectrometry corresponds to:

  • Mass divided by charge of an ion
  • Concentration of analyte in mg/mL
  • Molecular weight in g/mol exactly
  • Retention factor in chromatography

Correct Answer: Mass divided by charge of an ion

Q15. Which diagnostic fragment suggests presence of a benzyl group?

  • Sharp peak at m/z 91 (tropylium ion)
  • Strong signal at m/z 44 only
  • Peak cluster centered at m/z 200 due to bromine
  • No fragments below m/z 100

Correct Answer: Sharp peak at m/z 91 (tropylium ion)

Q16. In ESI mass spectrometry, which species is commonly observed rather than a radical cation?

  • Neutral molecular ion (M·0)
  • Deprotonated [M–H]– or protonated [M+H]+ ions
  • Only fragment radical cations from EI
  • Adduct-free molecular radicals exclusively

Correct Answer: Deprotonated [M–H]– or protonated [M+H]+ ions

Q17. A peak at m/z corresponding to [M+Na]+ indicates what in an ESI spectrum?

  • Loss of sodium from the molecule
  • An alkali metal adduct due to sodium present in solvent or glassware
  • Exclusive fragmentation of the sample
  • Contamination by chlorine

Correct Answer: An alkali metal adduct due to sodium present in solvent or glassware

Q18. Which fragmentation mechanism often produces an acylium ion (R–C≡O+)?

  • Fragmentation of nitroalkanes exclusively
  • Cleavage of amides and esters adjacent to the carbonyl
  • Alpha-cleavage next to an aromatic ring only
  • Isotopic exchange processes

Correct Answer: Cleavage of amides and esters adjacent to the carbonyl

Q19. What does high-resolution mass spectrometry (HRMS) allow that low-resolution MS does not?

  • Measurement of retention times with higher precision
  • Distinguishing ions with the same nominal mass by exact mass differences
  • Ionization of nonpolar gases only
  • Direct visualization of 3D molecular structure

Correct Answer: Distinguishing ions with the same nominal mass by exact mass differences

Q20. The presence of a strong peak at m/z 43 in an EI spectrum commonly indicates:

  • Formation of a benzyl cation
  • A propyl or acylium fragment like C3H7+ or CH3CO+
  • Loss of molecular oxygen
  • Isotopic interference from chlorine

Correct Answer: A propyl or acylium fragment like C3H7+ or CH3CO+

Q21. Which approach helps assign structures to fragment ions during interpretation?

  • Ignoring accurate mass and relying only on intensity
  • Comparing observed m/z and neutral losses with known fragmentation rules and formula calculation
  • Assuming every peak is an impurity
  • Only using UV spectra for confirmation

Correct Answer: Comparing observed m/z and neutral losses with known fragmentation rules and formula calculation

Q22. What neutral loss of 28 Da is often seen and may indicate loss of CO?

  • Loss of CH4
  • Loss of H2O
  • Loss of CO or C2H4 depending on context
  • Loss of NH3 exclusively

Correct Answer: Loss of CO or C2H4 depending on context

Q23. In-source fragmentation refers to:

  • Fragmentation occurring in the ion source before mass analysis
  • Fragmentation occurring only in the collision cell of MS/MS
  • Breaking of bonds during sample preparation only
  • Complete ion suppression leading to no signal

Correct Answer: Fragmentation occurring in the ion source before mass analysis

Q24. Retro-Diels–Alder fragmentation is most relevant to which class of compounds?

  • Simple alkanes without rings
  • Cyclic dienes or adducts derived from Diels–Alder reactions
  • Inorganic salts
  • Monosaccharides only

Correct Answer: Cyclic dienes or adducts derived from Diels–Alder reactions

Q25. What key evidence helps distinguish between isomeric compounds in MS?

  • Only exact mass without fragmentation patterns
  • Differences in fragmentation patterns, diagnostic ions, and MS/MS spectra
  • Number of carbon atoms from NMR only
  • Absence of isotope peaks

Correct Answer: Differences in fragmentation patterns, diagnostic ions, and MS/MS spectra

Q26. Which fragment is characteristic of loss of a methyl radical (•CH3) from a radical cation?

  • Decrease of 15 Da relative to the molecular ion
  • Increase of 15 Da relative to the molecular ion
  • Loss of 18 Da only
  • No mass change but change in intensity

Correct Answer: Decrease of 15 Da relative to the molecular ion

Q27. Which of the following increases the likelihood of observing a stable molecular ion in EI?

  • Very high volatility and low electron affinity
  • Presence of easily ionizable heteroatoms always prevents molecular ion formation
  • Conjugation and aromaticity that stabilize the radical cation
  • Only having tertiary alkyl groups

Correct Answer: Conjugation and aromaticity that stabilize the radical cation

Q28. Which tool or method is commonly used to predict fragmentation patterns for unknowns?

  • MS databases and in-silico fragmentation software along with chemical reasoning
  • Only NMR prediction tools
  • Visual inspection of color changes in solution
  • Thin layer chromatography visualization

Correct Answer: MS databases and in-silico fragmentation software along with chemical reasoning

Q29. A fragment at m/z 29 could commonly represent which ion in EI spectra?

  • NO2+ radical cation
  • Ethyl cation (C2H5+) or CHO+ (formyl) depending on context
  • Tropylium ion
  • Chlorine-containing cation

Correct Answer: Ethyl cation (C2H5+) or CHO+ (formyl) depending on context

Q30. When interpreting drug metabolites by MS, which strategy is most effective?

  • Assuming metabolites have identical mass to parent drug
  • Looking for expected neutral losses (e.g., +16 Da for oxidation), shifts in accurate mass, and diagnostic fragments
  • Relying only on retention time without MS data
  • Only measuring UV absorption changes

Correct Answer: Looking for expected neutral losses (e.g., +16 Da for oxidation), shifts in accurate mass, and diagnostic fragments

Leave a Comment