GC–MS, LC–MS and hyphenated techniques applications MCQs With Answer

Introduction

This quiz collection on GC–MS, LC–MS and other hyphenated techniques is tailored for M.Pharm students studying advanced spectral analysis. It emphasizes practical applications, instrumentation principles, ionization and fragmentation behavior, quantitative strategies and troubleshooting common analytical problems. Questions cover GC–MS and LC–MS coupling, interfaces, ion sources (EI, CI, ESI, APCI, MALDI), mass analyzers (quadrupole, TOF, ion trap, Orbitrap), hyphenated method development, metabolite/impurity identification, and regulatory considerations for bioanalysis and residue testing. Designed to test both conceptual understanding and applied skills, the MCQs will help consolidate learning for exams and real-world pharmaceutical analysis tasks.

Q1. Which component in a GC–MS system is primarily responsible for transferring the separated analytes from the gas chromatograph into the mass spectrometer without condensation or decomposition?

• Split/splitless injector
• Temperature-controlled transfer line
• Quadrupole mass filter
• Electron ionization filament

Correct Answer: Temperature-controlled transfer line

Q2. Which ionization technique is most appropriate for coupling with liquid chromatography when analyzing polar, thermally labile drug metabolites for sensitive MS/MS quantitation?

• Electron ionization (EI)
• Electrospray ionization (ESI)
• Chemical ionization (CI)
• MALDI

Correct Answer: Electrospray ionization (ESI)

Q3. In GC–MS analysis using electron ionization (EI), what is the main reason derivatization is often required for many pharmaceutical analytes?

• To increase molecular weight for better fragmentation
• To improve volatility and thermal stability
• To create stronger chromophores for UV detection
• To allow formation of metal adducts

Correct Answer: To improve volatility and thermal stability

Q4. Which mass analyzer provides the highest mass resolving power and is thus most useful for exact mass measurements and elemental composition determination in LC–HRMS workflows?

• Quadrupole
• Ion trap
• Time-of-flight (TOF) / Orbitrap
• Magnetic sector

Correct Answer: Time-of-flight (TOF) / Orbitrap

Q5. In LC–MS/MS quantitative bioanalysis, what is the major benefit of using multiple reaction monitoring (MRM) on a triple quadrupole instrument?

• It permits full-scan accurate mass acquisition
• It increases selectivity and sensitivity by monitoring specific precursor→product transitions
• It reduces the need for chromatographic separation entirely
• It directly measures molecular formula via isotope fine structure

Correct Answer: It increases selectivity and sensitivity by monitoring specific precursor→product transitions

Q6. Which of the following is a common cause of ion suppression in LC–ESI–MS and how can it be minimized?

• High column temperature; minimize by lowering temperature
• Co-eluting matrix components; minimize by sample cleanup and chromatography optimization
• Poor vacuum in MS; minimize by baking out the instrument
• In-source fragmentation; minimize by increasing collision energy

Correct Answer: Co-eluting matrix components; minimize by sample cleanup and chromatography optimization

Q7. When using chemical ionization (CI) in GC–MS, which statement best describes the typical appearance of the molecular ion compared to EI?

• CI typically produces a stronger, more intact [M]+• radical ion than EI
• CI typically yields protonated [M+H]+ or adduct ions, often with less fragmentation than EI
• CI causes complete fragmentation with no molecular ion observed
• CI and EI produce identical spectra for all compounds

Correct Answer: CI typically yields protonated [M+H]+ or adduct ions, often with less fragmentation than EI

Q8. For identification of unknown impurities using LC–MS, which complementary technique is most valuable to confirm functional groups when MS fragmentation is ambiguous?

• NMR spectroscopy
• UV–Vis spectrophotometry
• Gas chromatography with FID
• Flash chromatography

Correct Answer: NMR spectroscopy

Q9. Which interface is best suited to couple liquid chromatography to atmospheric pressure chemical ionization (APCI) for analysis of moderately nonpolar pharmaceuticals?

• Heated electrospray needle
• Corona discharge needle in vaporized LC effluent (APCI source)
• Electron impact ionization source
• Direct insertion probe

Correct Answer: Corona discharge needle in vaporized LC effluent (APCI source)

Q10. In GC–MS, the Kovats retention index is used primarily to:

• Correct mass spectra for detector response
• Standardize retention times relative to n-alkane standards for compound identification
• Measure column bleed at high temperature
• Quantify analytes without internal standards

Correct Answer: Standardize retention times relative to n-alkane standards for compound identification

Q11. Which strategy improves quantitative accuracy in LC–MS bioanalysis when matrix effects vary between samples?

• Use external calibration prepared in pure solvent only
• Use stable isotope-labeled internal standards that co-elute with analytes
• Rely solely on peak area without normalization
• Increase collision energy to remove matrix ions

Correct Answer: Use stable isotope-labeled internal standards that co-elute with analytes

Q12. High-resolution mass spectrometry (HRMS) aids metabolite identification mainly because it allows:

• Measurement of ion intensity without mass accuracy
• Exact mass measurement enabling elemental composition and formula determination
• Faster chromatographic separations
• Visualization of fragment ions in 3D plots

Correct Answer: Exact mass measurement enabling elemental composition and formula determination

Q13. Which hyphenated technique is most appropriate for direct analysis of large bio-macromolecules like intact proteins and complexes?

• GC–MS with EI
• LC–MS with electrospray or native MS conditions
• HPLC–UV only
• Paper chromatography–TLC

Correct Answer: LC–MS with electrospray or native MS conditions

Q14. In method development for LC–MS of a basic drug, adjusting mobile phase pH below the pKa of the analyte primarily affects:

• Ionization efficiency in ESI and retention on reversed-phase columns due to protonation
• The mass analyzer resolution
• The EI fragmentation pattern
• The column temperature stability

Correct Answer: Ionization efficiency in ESI and retention on reversed-phase columns due to protonation

Q15. Which MS/MS scanning mode is most useful in forensic toxicology for screening multiple known target drugs with high specificity?

• Full-scan single-stage MS
• Multiple reaction monitoring (MRM) on triple quadrupole
• Selected ion monitoring (SIM) on a single quadrupole without product ions
• Neutral loss scan on an ion trap

Correct Answer: Multiple reaction monitoring (MRM) on triple quadrupole

Q16. When coupling GC to MS, which vacuum stage is essential to maintain ion transmission and reduce collisional damping for high sensitivity?

• Atmospheric pressure region only
• Multi-stage vacuum system with progressively lower pressures (turbomolecular pumps)
• High-pressure liquid chamber
• Open-air ambient ionization without pumps

Correct Answer: Multi-stage vacuum system with progressively lower pressures (turbomolecular pumps)

Q17. Which fragmentation pathway is commonly observed in EI mass spectra of aromatic esters and can assist structure elucidation?

• McLafferty rearrangement leading to neutral loss and characteristic fragments
• Formation of stable protonated molecular ions only
• Complete absence of fragment ions due to stabilization
• Only water loss from the molecular ion

Correct Answer: McLafferty rearrangement leading to neutral loss and characteristic fragments

Q18. In LC–MS method validation for a bioanalytical assay, which parameter directly assesses matrix-related variability between different lots of biological matrix?

• Limit of detection (LOD)
• Matrix effect evaluation (matrix factor and normalized matrix factor)
• Chromatographic peak width
• Column static retention factor

Correct Answer: Matrix effect evaluation (matrix factor and normalized matrix factor)

Q19. Which approach helps identify positional isomers that share identical exact mass and similar MS/MS fragments in LC–HRMS workflows?

• Rely only on exact mass and ignore chromatographic retention
• Use chromatographic separation, retention time comparison with standards and orthogonal fragmentation techniques (e.g., MSn or ion mobility)
• Decrease resolving power to collapse isotopic patterns
• Use only single-stage MS with electron impact

Correct Answer: Use chromatographic separation, retention time comparison with standards and orthogonal fragmentation techniques (e.g., MSn or ion mobility)

Q20. Which practice is recommended when building a GC–MS library search for reliable compound identification in impurity profiling?

• Use spectra acquired under the same ionization conditions, column type and temperature program and include retention index data
• Combine spectra from different ion sources without annotation
• Exclude retention information and rely only on mass spectra
• Store only raw chromatograms without spectral metadata

Correct Answer: Use spectra acquired under the same ionization conditions, column type and temperature program and include retention index data

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