Quadrupole analyzer MCQs With Answer

Quadrupole analyzer MCQs With Answer

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Quadrupole Analyzer MCQs With Answer

Quadrupole mass analyzers are the backbone of many Modern Pharmaceutical Analytical Techniques, especially in LC–MS/MS for drug discovery, bioanalysis, metabolite profiling, and quality control. Their ability to deliver unit mass resolution, fast scanning, and robust quantitation makes them indispensable to M. Pharm students and researchers. This MCQ set focuses on the fundamentals and practical aspects of quadrupole analyzers: RF/DC operation, stability diagrams, rod geometry, mass filtering, MS/MS modes, tuning, pressure regimes, and performance trade-offs. Each question is crafted to reinforce conceptual clarity while helping you connect theory to real-world pharmaceutical analysis workflows. Use these MCQs to assess your understanding and sharpen exam readiness.

Q1. Which statement best describes the operating principle of a quadrupole mass filter?

  • Ions are separated by time-of-flight in a field-free drift region.
  • Ions with stable trajectories in a combined RF/DC electric field pass through; others are destabilized and ejected.
  • Ions are separated by cyclotron resonance in a magnetic field.
  • Ions are trapped and sequentially ejected by ramping RF-only voltage.

Correct Answer: Ions with stable trajectories in a combined RF/DC electric field pass through; others are destabilized and ejected.

Q2. How are voltages applied to the rods in a quadrupole mass filter?

  • Same RF phase to all rods; DC only to two rods.
  • Opposite DC potentials and radiofrequency voltages 180° out of phase applied to opposing rod pairs.
  • Only RF voltage applied; no DC.
  • A static magnetic field and DC applied simultaneously.

Correct Answer: Opposite DC potentials and radiofrequency voltages 180° out of phase applied to opposing rod pairs.

Q3. Which material is commonly used for quadrupole rods due to conductivity and mechanical stability?

  • Stainless steel
  • Aluminium oxide
  • Teflon
  • Glass

Correct Answer: Stainless steel

Q4. What is the typical RF frequency range used in quadrupole mass filters?

  • 1–3 MHz
  • 50–60 Hz
  • 100–500 MHz
  • 1–3 kHz

Correct Answer: 1–3 MHz

Q5. What is the role of the DC/RF ratio in a quadrupole mass filter?

  • Sets resolving power by selecting the slope through the stability diagram; higher ratio increases resolution but lowers transmission.
  • Only affects ion source ionization efficiency.
  • Determines the vacuum level required for operation.
  • Controls detector gain.

Correct Answer: Sets resolving power by selecting the slope through the stability diagram; higher ratio increases resolution but lowers transmission.

Q6. The dimensionless Mathieu parameters (a and q) that define ion stability in a quadrupole depend on:

  • Only the ion source temperature.
  • RF amplitude, DC voltage, RF frequency, rod radius, and m/z.
  • The detector voltage and electron multiplier gain.
  • Collision gas pressure only.

Correct Answer: RF amplitude, DC voltage, RF frequency, rod radius, and m/z.

Q7. To scan m/z upward in a quadrupole mass filter, one typically:

  • Increases RF and DC amplitudes proportionally at a constant ratio.
  • Decreases RF amplitude while increasing DC.
  • Keeps RF constant and steps DC only.
  • Changes the RF frequency only.

Correct Answer: Increases RF and DC amplitudes proportionally at a constant ratio.

Q8. In triple quadrupole MS/MS, the second quadrupole (Q2) typically operates:

  • As a magnetic sector.
  • In RF-only mode as a collision cell for CID.
  • With high DC to mass-filter product ions.
  • As an Orbitrap analyzer.

Correct Answer: In RF-only mode as a collision cell for CID.

Q9. Which MS/MS experiment is most commonly used for quantitative LC–MS/MS bioanalysis with triple quadrupoles?

  • Neutral loss scan.
  • Multiple reaction monitoring (MRM/SRM).
  • Precursor ion scan.
  • Full scan MS1.

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

Q10. What is a typical operating pressure in the mass-filtering quadrupole region (Q1 or Q3)?

  • ~1 Torr
  • ~10−5 Torr
  • ~10−1 Torr
  • ~10−9 Torr

Correct Answer: ~10−5 Torr

Q11. The upper m/z range of a quadrupole mass filter is primarily limited by:

  • The length of the collision cell only.
  • Maximum RF voltage, RF frequency, and rod radius (r0).
  • Detector saturation.
  • Source temperature.

Correct Answer: Maximum RF voltage, RF frequency, and rod radius (r0).

Q12. A single quadrupole mass analyzer typically achieves:

  • High-resolution (R > 50,000) accurate mass measurements.
  • Unit mass resolution across a wide m/z range.
  • Only elemental analysis of inorganic ions.
  • No capability to operate in SIM mode.

Correct Answer: Unit mass resolution across a wide m/z range.

Q13. The main trade-off when increasing resolution in a quadrupole mass filter is:

  • Increased mass accuracy without signal loss.
  • Higher transmission and better sensitivity.
  • Reduced ion transmission and sensitivity.
  • Increased mass range at constant voltages.

Correct Answer: Reduced ion transmission and sensitivity.

Q14. The commonly used calibrant/tuning compound for quadrupole MS is:

  • Perfluorotributylamine (PFTBA).
  • Sodium formate clusters.
  • Caesium iodide.
  • Anthracene.

Correct Answer: Perfluorotributylamine (PFTBA).

Q15. Compared with a 3D ion trap, a linear quadrupole mass filter:

  • Stores ions and ejects them by resonance excitation.
  • Transmits only ions within a stability window while others are destabilized.
  • Has built-in capability for multiple harmonic resonance ejection.
  • Requires helium buffer gas at mTorr to function.

Correct Answer: Transmits only ions within a stability window while others are destabilized.

Q16. In a triple quadrupole product-ion scan, the roles of the quadrupoles are:

  • Q1 is set to RF-only; Q3 scans precursors.
  • Q1 selects the precursor; Q2 fragments it; Q3 scans the product ions.
  • Q1 scans product ions while Q3 isolates the precursor.
  • All three quadrupoles operate in RF-only mode.

Correct Answer: Q1 selects the precursor; Q2 fragments it; Q3 scans the product ions.

Q17. Why are pre- and post-filters (or fringe-field lenses) used around a quadrupole?

  • To cool ions by laser cooling.
  • To minimize fringe-field effects, improve transmission, and reduce peak tailing.
  • To generate higher harmonic RF for better selectivity.
  • To increase collision energy for CID.

Correct Answer: To minimize fringe-field effects, improve transmission, and reduce peak tailing.

Q18. Which statement about rod geometry and field quality is true?

  • Perfect hyperbolic rods give ideal quadrupole fields, but machined circular rods with appropriate radius ratio closely approximate them.
  • Square rods increase resolution without affecting transmission.
  • Thin wire rods maximize field linearity.
  • Rod geometry has no effect on mass accuracy.

Correct Answer: Perfect hyperbolic rods give ideal quadrupole fields, but machined circular rods with appropriate radius ratio closely approximate them.

Q19. Which stability region of the a–q diagram is typically used for quadrupole mass filtering?

  • The second stability region provides highest transmission and is routinely used.
  • The first stability region near the tip is chosen to balance resolution and transmission.
  • No defined stability regions are used; all ions are always stable.
  • The third stability region yields unit mass resolution and is standard.

Correct Answer: The first stability region near the tip is chosen to balance resolution and transmission.

Q20. In LC–MS/MS using MRM on a triple quadrupole, monitoring many transitions per cycle most likely leads to:

  • Longer dwell times per transition and improved signal-to-noise.
  • Shorter dwell times and potential loss of sensitivity and peak definition.
  • Increased mass resolution without changing sensitivity.
  • No effect on data quality or quantitation.

Correct Answer: Shorter dwell times and potential loss of sensitivity and peak definition.

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