Instrumentation of FTIR spectrometer MCQs With Answer

Instrumentation of FTIR spectrometer MCQs With Answer

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Instrumentation of FTIR Spectrometer MCQs With Answer

The Fourier Transform Infrared (FTIR) spectrometer is a core tool in Modern Pharmaceutical Analytical Techniques for identifying functional groups, verifying raw materials, and monitoring processes. This quiz focuses on the instrumentation of FTIR—covering sources, interferometer design, beam splitters, detectors, spectral resolution, apodization, ATR accessories, and advantages of FTIR over dispersive IR. Designed for M. Pharm students, the questions go beyond definitions to probe how each component affects data quality, sensitivity, and accuracy. Practicing these MCQs will strengthen your understanding of FTIR architecture, help you troubleshoot spectral issues, and guide you in selecting appropriate accessories and settings for pharmaceutical analysis.

Q1. What is the primary role of the Michelson interferometer in an FTIR spectrometer?

  • Generate an interferogram by modulating optical path difference between two beams
  • Disperse light into component wavelengths using a prism
  • Amplify the detector signal to increase sensitivity
  • Eliminate atmospheric CO₂ bands by destructive interference

Correct Answer: Generate an interferogram by modulating optical path difference between two beams

Q2. Which radiation source is most commonly used for mid-IR FTIR measurements?

  • Globar (silicon carbide) source
  • Tungsten–halogen lamp
  • Deuterium lamp
  • Excimer laser

Correct Answer: Globar (silicon carbide) source

Q3. The most common beamsplitter material used in mid-IR FTIR instruments is:

  • Potassium bromide (KBr), often with a germanium coating
  • Calcium fluoride (CaF₂)
  • Fused silica
  • Magnesium fluoride (MgF₂)

Correct Answer: Potassium bromide (KBr), often with a germanium coating

Q4. Which detector is widely used in mid-IR FTIR for room-temperature operation?

  • DTGS (deuterated triglycine sulfate) pyroelectric detector
  • MCT (mercury cadmium telluride) photoconductive detector
  • Photomultiplier tube
  • CCD array

Correct Answer: DTGS (deuterated triglycine sulfate) pyroelectric detector

Q5. The internal reference used to calibrate the wavenumber scale in an FTIR spectrometer is typically a:

  • Helium–neon laser at 632.8 nm
  • Nd:YAG laser at 1064 nm
  • Diode laser at 1550 nm
  • Argon ion laser at 488 nm

Correct Answer: Helium–neon laser at 632.8 nm

Q6. The improved signal-to-noise ratio from simultaneous measurement of all frequencies in FTIR is known as the:

  • Fellgett (multiplex) advantage
  • Nyquist advantage
  • Lambert–Beer advantage
  • Stark advantage

Correct Answer: Fellgett (multiplex) advantage

Q7. In FTIR, spectral resolution is primarily determined by the:

  • Maximum optical path difference (mirror travel) in the interferometer
  • Width of entrance and exit slits
  • Detector bandwidth
  • Source temperature

Correct Answer: Maximum optical path difference (mirror travel) in the interferometer

Q8. The typical wavenumber range for mid-IR FTIR analysis is:

  • 4000–400 cm⁻¹
  • 12,500–4000 cm⁻¹
  • 200–10 cm⁻¹
  • 50,000–12,500 cm⁻¹

Correct Answer: 4000–400 cm⁻¹

Q9. The primary purpose of apodization in FTIR data processing is to:

  • Reduce sidelobes (ringing) from sinc line shapes to improve peak appearance
  • Increase optical throughput of the interferometer
  • Change the sampling frequency of the He–Ne reference
  • Calibrate the baseline to zero absorbance

Correct Answer: Reduce sidelobes (ringing) from sinc line shapes to improve peak appearance

Q10. Why is the sample compartment of an FTIR commonly purged with dry air or nitrogen, or evacuated?

  • To remove atmospheric H₂O and CO₂ that cause interfering absorption bands
  • To increase the refractive index of the beam path
  • To prevent laser drift due to temperature changes
  • To enhance the atomic emission lines

Correct Answer: To remove atmospheric H₂O and CO₂ that cause interfering absorption bands

Q11. In ATR-FTIR, which crystal material offers broad chemical compatibility and high durability for routine pharma use?

  • KBr
  • NaCl
  • Diamond
  • Quartz

Correct Answer: Diamond

Q12. Which of the following is a commonly used apodization function in FTIR?

  • Happ–Genzel
  • Z-transform
  • Kalman filter
  • Four-point derivative

Correct Answer: Happ–Genzel

Q13. The term “Connes advantage” in FTIR refers to:

  • High wavenumber accuracy from laser-referenced interferometer scanning
  • Improved sensitivity due to cooled detectors
  • Higher throughput from wide slits
  • Better sampling of aqueous solutions using ATR

Correct Answer: High wavenumber accuracy from laser-referenced interferometer scanning

Q14. In an interferogram, the intense “centerburst” region corresponds to:

  • Zero optical path difference (ZOPD)
  • Maximum mirror displacement
  • Detector DC offset
  • High-frequency electronic noise

Correct Answer: Zero optical path difference (ZOPD)

Q15. Why is an MCT detector often cooled with liquid nitrogen in FTIR instruments?

  • To prevent water condensation on the beamsplitter
  • To reduce thermal noise and increase sensitivity and speed
  • To improve laser frequency stability
  • To enhance beamsplitter reflectivity

Correct Answer: To reduce thermal noise and increase sensitivity and speed

Q16. For near-IR FTIR configurations, an appropriate beamsplitter and source combination is:

  • CaF₂ beamsplitter with tungsten–halogen source
  • KBr beamsplitter with deuterium lamp
  • ZnSe beamsplitter with Globar source
  • Fused silica beamsplitter with Nernst glower

Correct Answer: CaF₂ beamsplitter with tungsten–halogen source

Q17. In FTIR data processing, zero-filling is used to:

  • Increase true spectral resolution
  • Increase digital point density to refine peak position display without changing true resolution
  • Reduce detector noise at the source
  • Calibrate the wavenumber axis using standards

Correct Answer: Increase digital point density to refine peak position display without changing true resolution

Q18. A DRIFTS accessory in FTIR is most suitable for analyzing:

  • Aqueous solutions in transmission cells
  • Solid pellets formed with KBr
  • Gases in long-path cells
  • Finely powdered solids and rough surfaces by diffuse reflectance

Correct Answer: Finely powdered solids and rough surfaces by diffuse reflectance

Q19. In the Michelson interferometer, which component both splits the incoming beam and recombines the returning beams?

  • Aperture
  • Beamsplitter
  • Chopper
  • Attenuator

Correct Answer: Beamsplitter

Q20. Which parameter must remain well controlled during an FTIR scan to maintain an accurate frequency (wavenumber) scale?

  • Constant moving mirror velocity monitored by the reference laser
  • Constant detector bias voltage
  • Fixed slit width in the sample compartment
  • Ambient humidity at 50%

Correct Answer: Constant moving mirror velocity monitored by the reference laser

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