Instrumentation and applications of mass spectrometry MCQs With Answer

Introduction: Mass spectrometry is a core analytical tool in pharmaceutical sciences, combining ionization techniques, mass analyzers and detectors to identify and quantify drugs, metabolites and biomolecules. This introduction covers instrumentation and applications relevant to B. Pharm students: ion sources (EI, ESI, MALDI, APCI), mass analyzers (quadrupole, TOF, Orbitrap, ion trap, FT‑ICR), tandem MS for structural elucidation, and hyphenated techniques like LC‑MS and GC‑MS. Emphasis is on high‑resolution mass spectrometry, quantitative assays (SRM/MRM), pharmacokinetics, metabolite identification, proteomics, and matrix effects such as ion suppression. Understanding these principles is essential for drug analysis, method development and interpretation of spectra. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which components are essential parts of a typical mass spectrometer?

• Sample injector, chromatographic column, detector, and data logger
• Ion source, mass analyzer, detector, vacuum system and data system
• Ion source, flame ionization detector, pump, and spectrophotometer
• Chromatograph, furnace, photodiode array and mass filter

Correct Answer: Ion source, mass analyzer, detector, vacuum system and data system

Q2. What does the term m/z represent in mass spectrometry?

• Mass divided by atomic number
• Momentum per unit charge
• Mass-to-charge ratio of an ion
• Molar concentration of analyte

Correct Answer: Mass-to-charge ratio of an ion

Q3. Which ionization technique is most suitable for volatile, thermally stable small molecules and widely used in GC-MS?

• Electrospray Ionization (ESI)
• MALDI (Matrix-Assisted Laser Desorption/Ionization)
• Electron Ionization (EI)
• Atmospheric Pressure Chemical Ionization (APCI)

Correct Answer: Electron Ionization (EI)

Q4. Which ionization method is considered a “soft” technique that commonly produces multiply charged ions for large biomolecules?

• Electron Ionization (EI)
• Electrospray Ionization (ESI)
• Field Ionization (FI)
• Fast Atom Bombardment (FAB)

Correct Answer: Electrospray Ionization (ESI)

Q5. How does a quadrupole mass analyzer separate ions?

• By measuring flight time of ions across a field-free region
• By trapping ions in a magnetic field and measuring cyclotron frequency
• By using oscillating RF and DC electric fields to allow only a specific m/z to pass
• By detecting ions with a time-dependent image current

Correct Answer: By using oscillating RF and DC electric fields to allow only a specific m/z to pass

Q6. What is the operating principle of a time-of-flight (TOF) mass analyzer?

• Ions are separated by differential diffusion rates
• Ions are separated based on their travel time over a fixed distance after acceleration
• Ions are trapped and ejected sequentially by RF fields
• Ions are filtered via magnetic sector only

Correct Answer: Ions are separated based on their travel time over a fixed distance after acceleration

Q7. Which expression defines mass resolution in mass spectrometry?

• m × Δm
• m/Δm (where Δm is peak width at a specified height)
• Δm/m
• Absolute mass error in Daltons

Correct Answer: m/Δm (where Δm is peak width at a specified height)

Q8. High-resolution mass spectrometry (HRMS) is most useful for which task?

• Separating enantiomers
• Determining exact molecular formula from accurate mass
• Increasing chromatographic retention
• Measuring optical rotation of compounds

Correct Answer: Determining exact molecular formula from accurate mass

Q9. What is the main purpose of tandem mass spectrometry (MS/MS) in drug analysis?

• To increase chromatographic separation efficiency
• To generate fragment ions for structural elucidation and selective quantitation
• To cool ions prior to detection
• To convert ions to neutral molecules

Correct Answer: To generate fragment ions for structural elucidation and selective quantitation

Q10. Collision-induced dissociation (CID) fragments ions by which mechanism?

• Electron capture leading to radical ions
• Absorption of photons from a laser
• Collisions with an inert gas converting kinetic energy to internal energy and breaking bonds
• Magnetic resonance of ion cyclotron motion

Correct Answer: Collisions with an inert gas converting kinetic energy to internal energy and breaking bonds

Q11. Which MS/MS mode is commonly used for highly selective and sensitive quantitation in LC‑MS/MS assays?

• Full-scan TOF
• Selected ion monitoring (SIM)
• Selected reaction monitoring / Multiple reaction monitoring (SRM/MRM)
• Neutral loss scan

Correct Answer: Selected reaction monitoring / Multiple reaction monitoring (SRM/MRM)

Q12. Which isotopic pattern in a mass spectrum strongly indicates the presence of bromine in a molecule?

• A single dominant peak with no satellites
• Two peaks of approximately equal intensity separated by 2 Da
• Peaks separated by 1 Da with 3:1 ratio
• A cluster of peaks due to polyisotopic carbon only

Correct Answer: Two peaks of approximately equal intensity separated by 2 Da

Q13. What is the monoisotopic mass of a molecule?

• The average mass of the molecule considering natural isotope abundance
• The mass including adducts like Na+ or K+
• The exact mass calculated using the most abundant isotopes (e.g., 12C, 1H)
• The nominal integer mass rounded to the nearest Dalton

Correct Answer: The exact mass calculated using the most abundant isotopes (e.g., 12C, 1H)

Q14. In a mass spectrum, what is the “base peak”?

• The heaviest ion detected
• The most intense peak in the spectrum, set to 100% relative abundance
• The peak corresponding to the solvent
• The lowest m/z peak observed

Correct Answer: The most intense peak in the spectrum, set to 100% relative abundance

Q15. Mass accuracy in high‑resolution MS is commonly reported in which unit?

• Daltons (Da)
• Minutes
• Parts per million (ppm)
• Electron volts (eV)

Correct Answer: Parts per million (ppm)

Q16. Which type of internal standard is preferred for quantitative LC‑MS assays to correct for extraction and ionization variability?

• Structurally unrelated compound with similar retention time
• Stable‑isotope labeled analogue of the analyte
• External calibration curve only
• UV-active dye

Correct Answer: Stable‑isotope labeled analogue of the analyte

Q17. What causes ion suppression in electrospray ionization LC‑MS analyses?

• Insufficient vacuum in the mass analyzer
• Matrix co-eluting compounds competing for charge and reducing analyte ionization efficiency
• Too high resolving power
• Use of a stable‑isotope internal standard

Correct Answer: Matrix co-eluting compounds competing for charge and reducing analyte ionization efficiency

Q18. MALDI is particularly advantageous for which application?

• Quantitative small molecule analysis in plasma
• Analyzing large proteins and peptides with minimal fragmentation and for imaging mass spectrometry
• Direct gas-phase ionization of volatile solvents
• Measuring isotopic ratios in inorganic salts

Correct Answer: Analyzing large proteins and peptides with minimal fragmentation and for imaging mass spectrometry

Q19. Which statement best describes the Orbitrap mass analyzer?

• Ions are separated by magnetic sector fields only
• Ions oscillate around a central spindle and frequency of oscillation is used to determine m/z with high resolution
• Ions are detected by time-of-flight after a pulsed extraction
• Ions are destroyed upon collision in this analyzer

Correct Answer: Ions oscillate around a central spindle and frequency of oscillation is used to determine m/z with high resolution

Q20. What gives FT‑ICR MS its exceptionally high resolving power?

• Use of RF-only quadrupoles
• Trapping ions in a strong magnetic field and measuring ion cyclotron resonance frequencies
• Very short flight paths in a TOF analyzer
• Use of multiple electron multipliers in series

Correct Answer: Trapping ions in a strong magnetic field and measuring ion cyclotron resonance frequencies

Q21. Which detector is commonly used to amplify ion signals in many mass spectrometers?

• Thermocouple detector
• Electron multiplier / microchannel plate
• Flame ionization detector
• NMR coil

Correct Answer: Electron multiplier / microchannel plate

Q22. Which adducts are commonly observed in positive‑mode ESI spectra of small molecules?

• Cl− and Br− adducts
• Na+, K+ and NH4+ adducts
• Protonless radical cations only
• Sulfate and phosphate adducts exclusively

Correct Answer: Na+, K+ and NH4+ adducts

Q23. What is selected ion monitoring (SIM) used for in mass spectrometry?

• Recording full mass spectra for unknown screening
• Monitoring specific m/z values to enhance sensitivity for target analytes
• Measuring ion mobility in gas phase
• Calibrating the vacuum system

Correct Answer: Monitoring specific m/z values to enhance sensitivity for target analytes

Q24. Mass spectrometry imaging (MSI) enables which capability important in pharmaceutical research?

• Determination of enantiomeric excess in tablets
• Mapping spatial distribution of drugs and metabolites in tissue sections
• Replacing LC separation in all quantitative assays
• Direct measurement of oral bioavailability without sampling

Correct Answer: Mapping spatial distribution of drugs and metabolites in tissue sections

Q25. In GC‑MS with EI ionization, why are fragment ions often abundant?

• EI is a soft ionization that preserves only molecular ions
• EI imparts high internal energy causing extensive fragmentation useful for structural identification
• GC carriers quench fragmentation entirely
• Samples are ionized by proton transfer only

Correct Answer: EI imparts high internal energy causing extensive fragmentation useful for structural identification

Q26. How does increasing collision energy in MS/MS typically affect fragmentation?

• Produces fewer and larger fragment ions
• Generates more extensive fragmentation, often yielding smaller fragment ions
• Has no effect on fragmentation pattern
• Prevents any fragmentation from occurring

Correct Answer: Generates more extensive fragmentation, often yielding smaller fragment ions

Q27. What does dynamic range of a mass spectrometer describe?

• The physical size range of ions that can be admitted
• The ratio between the largest and smallest ion signals that can be measured accurately
• The number of mass analyzers in the instrument
• The range of temperatures tolerated by the ion source

Correct Answer: The ratio between the largest and smallest ion signals that can be measured accurately

Q28. Why are multiply charged ions advantageous when analyzing large proteins by ESI?

• They increase the molecular weight measured in m/z space
• They reduce the observed m/z values so large masses fall within the instrument’s m/z range
• They eliminate the need for fragmentation
• They always produce single, simple peaks

Correct Answer: They reduce the observed m/z values so large masses fall within the instrument’s m/z range

Q29. Which calibration strategy generally yields the best mass accuracy during an LC‑MS run?

• External calibration performed once per week
• No calibration; rely on nominal mass only
• Internal calibration using known reference masses added to each sample or infused
• Using theoretical masses without standards

Correct Answer: Internal calibration using known reference masses added to each sample or infused

Q30. Which of the following is a key application of mass spectrometry in pharmacokinetics?

• Measuring dissolution profiles using UV alone
• Quantifying drug and metabolite concentrations in biological matrices to determine ADME parameters
• Determining tablet hardness
• Measuring pH of gastric fluids without sample prep

Correct Answer: Quantifying drug and metabolite concentrations in biological matrices to determine ADME parameters

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