Mass analysers: FT-ICR MCQs With Answer

Mass analysers: FT-ICR MCQs With Answer

This quiz set focuses on Fourier Transform Ion Cyclotron Resonance (FT‑ICR) mass spectrometry — a cornerstone technique in high‑resolution MS for M.Pharm students. The questions cover fundamental physics (cyclotron motion, Penning trap), instrument components (magnet, ICR cell, excitation/detection), performance factors (resolving power, mass accuracy, transient length, space‑charge), data processing (Fourier transform, apodization, zero‑filling) and practical considerations (vacuum, calibration, fragmentation methods). Items are designed to deepen understanding beyond superficial facts and prepare you for exams and practical use of FT‑ICR in pharmaceutical analysis, proteomics, and structural characterization of complex molecules.

Q1. What physical quantity primarily determines the cyclotron frequency of an ion in an FT‑ICR cell?

• The ion’s kinetic energy
• The magnetic field strength and the ion’s mass-to-charge ratio
• The applied radiofrequency amplitude
• The cell dimensions

Correct Answer: (The magnetic field strength and the ion’s mass-to-charge ratio)

Q2. Which equation correctly relates the cyclotron frequency (f) to charge (q), magnetic field (B), and mass (m)?

• f = qB/(2πm)
• f = m/(qB)
• f = q/(mB^2)
• f = 2πqB/m^2

Correct Answer: (f = qB/(2πm))

Q3. In FT‑ICR, which detector principle is used to observe ion motion without destroying the ions?

• Electron multiplier detection
• Image current detection on trap electrodes
• Photomultiplier tube detection
• Faraday cup with ion collection

Correct Answer: (Image current detection on trap electrodes)

Q4. Which factor most directly increases the mass resolving power in an FT‑ICR experiment?

• Shorter transient acquisition time
• Higher magnetic field strength and longer transient time
• Increasing ion source temperature
• Using a smaller ICR cell volume only

Correct Answer: (Higher magnetic field strength and longer transient time)

Q5. What is the main role of excitation pulses in an FT‑ICR experiment?

• To neutralize unwanted background gas
• To increase ion internal energy for fragmentation
• To coherently increase ion cyclotron radii so ions induce larger image currents
• To cool ions to the trap center

Correct Answer: (To coherently increase ion cyclotron radii so ions induce larger image currents)

Q6. Space‑charge effects in FT‑ICR primarily cause which of the following problems?

• Improved vacuum conditions
• Peak broadening and frequency shifts leading to reduced mass accuracy
• Faster ion cyclotron motion
• Reduced detector sensitivity only

Correct Answer: (Peak broadening and frequency shifts leading to reduced mass accuracy)

Q7. Which ICR cell design is intended to reduce ion cloud dephasing and improve transient lifetimes?

• Linear quadrupole cell
• Infinity cell (or compensated open cell)
• Cylindrical cage without compensation
• Faraday cup cell

Correct Answer: (Infinity cell (or compensated open cell))

Q8. Why is ultra‑high vacuum required in FT‑ICR instruments?

• To cool the superconducting magnet
• To minimize ion–neutral collisions that damp cyclotron motion and shorten transients
• To increase the ionization efficiency of ESI
• To stabilize the ion source temperature

Correct Answer: (To minimize ion–neutral collisions that damp cyclotron motion and shorten transients)

Q9. What data processing step is commonly applied to the time‑domain transient before Fourier transformation to reduce spectral leakage?

• Baseline subtraction only
• Apodization (windowing) of the transient
• Increasing ion injection time
• Applying stronger excitation pulses

Correct Answer: (Apodization (windowing) of the transient)

Q10. Zero‑filling of the transient in FT processing primarily provides what benefit?

• It increases the actual instrumental resolving power
• It improves apparent digital resolution and peak interpolation in the frequency domain
• It reduces space‑charge effects
• It shortens acquisition time

Correct Answer: (It improves apparent digital resolution and peak interpolation in the frequency domain)

Q11. Which fragmentation method is commonly used in FT‑ICR for MS/MS experiments without collisional cell ejection?

• Surface‑induced dissociation (SID) only
• Sustained Off‑Resonance Irradiation (SORI) CID and IRMPD
• Electron multiplier dissociation
• Gas‑phase thermal dissociation

Correct Answer: (Sustained Off‑Resonance Irradiation (SORI) CID and IRMPD)

Q12. Which of these statements about mass accuracy in FT‑ICR is true?

• Mass accuracy is independent of magnetic field stability
• High mass accuracy requires careful calibration and magnetic field stability
• Mass accuracy can be improved only by increasing ion current
• Mass accuracy is solely determined by instrument vacuum

Correct Answer: (High mass accuracy requires careful calibration and magnetic field stability)

Q13. Internal calibration in FT‑ICR uses:

• Calibration ions measured in a separate run
• Known reference ions introduced and measured in the same transient as analyte ions
• Only mathematical post‑processing without standards
• Calibration at a different magnetic field strength

Correct Answer: (Known reference ions introduced and measured in the same transient as analyte ions)

Q14. Which phenomenon produces harmonics and sidebands in an FT‑ICR mass spectrum?

• Perfectly homogeneous magnetic field
• Nonlinear ion motion, imperfect excitation/detection and field inhomogeneities
• Ultra‑high vacuum conditions
• Use of image current detection exclusively

Correct Answer: (Nonlinear ion motion, imperfect excitation/detection and field inhomogeneities)

Q15. The relationship between resolving power (R), transient duration (T), and cyclotron frequency (f) in FT‑ICR qualitatively indicates that:

• R decreases with longer T
• R is roughly proportional to f×T (longer transient and higher frequency give higher R)
• R depends only on ion charge state, not T
• R increases only with larger cell volume

Correct Answer: (R is roughly proportional to f×T (longer transient and higher frequency give higher R))

Q16. Which of the following is a limitation specific to FT‑ICR compared with other high‑resolution analyzers?

• Lower achievable resolving power
• Large, expensive superconducting magnets and requirement for highly homogeneous fields
• Inability to analyze large biomolecules
• Incompatibility with electrospray ionization

Correct Answer: (Large, expensive superconducting magnets and requirement for highly homogeneous fields)

Q17. What is the effect of slight magnetic field drift during an FT‑ICR transient?

• No observable effect on mass accuracy
• It causes frequency shifts and reduces mass accuracy unless corrected
• It shortens the m/z range detectable only
• It increases signal‑to‑noise ratio

Correct Answer: (It causes frequency shifts and reduces mass accuracy unless corrected)

Q18. Which calibration approach can correct non‑linear frequency‑to‑mass conversion across a wide m/z range in FT‑ICR?

• Single‑point external calibration
• Multi‑point internal calibration using several reference masses
• Ignoring calibration and using theoretical values
• Only adjusting vacuum pressure

Correct Answer: (Multi‑point internal calibration using several reference masses)

Q19. In the context of signal processing for FT‑ICR, what is phase correction intended to achieve?

• Remove ions with low abundance
• Convert complex Fourier output to a true absorptive mode spectrum for improved peak shapes
• Increase magnetic field homogeneity
• Speed up ion injection

Correct Answer: (Convert complex Fourier output to a true absorptive mode spectrum for improved peak shapes)

Q20. How does increasing the ion charge state (z) of a peptide influence its cyclotron frequency and detectability in FT‑ICR?

• Higher charge lowers cyclotron frequency and reduces detectability
• Higher charge increases cyclotron frequency for a given m, often improving detection sensitivity and resolving power at a given m/z
• Charge state has no effect on frequency or detectability
• Higher charge always causes immediate fragmentation preventing detection

Correct Answer: (Higher charge increases cyclotron frequency for a given m, often improving detection sensitivity and resolving power at a given m/z)

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