Calibration of IR spectrophotometer MCQs With Answer

Calibration of IR spectrophotometer MCQs With Answer

Calibration of IR spectrophotometer is essential for reliable qualitative and quantitative analysis in pharmaceutical practice. This introduction covers key concepts such as wavelength accuracy, photometric accuracy, resolution, stray light, baseline stability, use of reference standards (e.g., polystyrene film), instrument qualification (IQ/OQ/PQ), validation, and routine performance verification. B.Pharm students should understand FTIR vs dispersive instruments, detector types, sample preparation (KBr, ATR), and frequency of calibration to ensure precision, linearity, sensitivity, and regulatory compliance. Mastery of these calibration principles supports accurate drug identification, assay development, and quality control. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which standard is most commonly used for verifying wavelength accuracy of an FTIR spectrophotometer?

• Polystyrene film standard
• Sodium chloride crystal
• Potassium bromide pellet
• Polytetrafluoroethylene (PTFE) powder

Correct Answer: Polystyrene film standard

Q2. Photometric accuracy in an IR spectrophotometer refers to:

• The accuracy of recorded wavelength positions
• The accuracy of absorbance or transmittance measurements
• The mechanical alignment of the interferometer
• The resolution setting of the instrument

Correct Answer: The accuracy of absorbance or transmittance measurements

Q3. Which test primarily detects stray light in an IR spectrophotometer?

• Baseline stability test
• Noise measurement
• Stray light test using narrow-band filters
• Resolution test with polystyrene

Correct Answer: Stray light test using narrow-band filters

Q4. For routine qualification, IQ/OQ/PQ stands for:

• Installation, Operational, Performance Qualification
• Instrument, Operational, Performance Quality
• Installation, Output, Product Qualification
• Instrumentation, Operation, Protocol Qualification

Correct Answer: Installation, Operational, Performance Qualification

Q5. Which detector is known for higher sensitivity and requires cooling in FTIR instruments?

• DTGS (deuterated triglycine sulfate)
• MCT (mercury cadmium telluride)
• InGaAs
• Photomultiplier tube

Correct Answer: MCT (mercury cadmium telluride)

Q6. What is the main advantage of ATR sampling in IR spectroscopy for pharmaceutical solids?

• Requires thin KBr pellets
• Non-destructive analysis with minimal sample preparation
• Provides better wavelength calibration than transmission
• Eliminates the need for baseline correction

Correct Answer: Non-destructive analysis with minimal sample preparation

Q7. Which parameter is most affected by misalignment of the interferometer mirrors?

• Photometric linearity
• Wavelength accuracy and resolution
• Detector noise
• Sample thickness

Correct Answer: Wavelength accuracy and resolution

Q8. In calibration, a resolution test commonly uses which spectral feature of polystyrene?

• Broad O–H stretching band
• Sharp CH bending bands around 695 cm⁻¹
• CO₂ interference peaks
• Mid-IR baseline slope

Correct Answer: Sharp CH bending bands around 695 cm⁻¹

Q9. Baseline stability assessment over time primarily evaluates:

• Wavelength position repeatability
• Long-term drift in instrument response
• Sensitivity to sample matrix effects
• Resolution at high wavenumbers

Correct Answer: Long-term drift in instrument response

Q10. Which factor least affects IR spectral quality during routine calibration?

• Ambient humidity and CO₂
• Detector temperature fluctuations
• Sample color under visible light
• Beam splitter condition

Correct Answer: Sample color under visible light

Q11. What is the purpose of background collection before sample measurement?

• To calibrate photometric accuracy only
• To remove instrument and atmospheric contributions from sample spectrum
• To align the interferometer mirrors
• To validate detector cooling

Correct Answer: To remove instrument and atmospheric contributions from sample spectrum

Q12. Which practice helps minimize water vapor interference in IR spectra?

• Using wet KBr pellets
• Purging the spectrometer with dry air or nitrogen
• Increasing resolution to maximum
• Shortening the background scan time

Correct Answer: Purging the spectrometer with dry air or nitrogen

Q13. Photometric linearity checks ensure:

• Detector responds linearly to different radiant intensities
• Wavelength assignments are accurate
• Sample pellet density is constant
• Resolution remains stable across scans

Correct Answer: Detector responds linearly to different radiant intensities

Q14. In single-beam vs double-beam IR spectrophotometers, the double-beam design primarily provides:

• Higher spectral resolution than single-beam
• Real-time compensation for source fluctuations
• Lower detector sensitivity
• Elimination of need for background scans

Correct Answer: Real-time compensation for source fluctuations

Q15. During instrument validation, limit of detection (LOD) in IR is most related to:

• Wavenumber calibration only
• Signal-to-noise ratio of small peaks
• The size of the KBr pellet
• Color of the sample

Correct Answer: Signal-to-noise ratio of small peaks

Q16. Resolution in FTIR is expressed in:

• Nanometers (nm)
• Wavenumbers (cm⁻¹)
• Hertz (Hz)
• Percentage transmission (%)

Correct Answer: Wavenumbers (cm⁻¹)

Q17. Which maintenance item directly affects spectral throughput and sensitivity?

• Changing the computer monitor
• Cleaning or replacing the source and detector optics
• Updating spectral libraries only
• Rearranging the laboratory furniture

Correct Answer: Cleaning or replacing the source and detector optics

Q18. Calibration transfer between two FTIR instruments requires matching:

• Sample color and smell
• Instrument configuration, resolution, and spectral processing
• Only the detector brand
• Different background files

Correct Answer: Instrument configuration, resolution, and spectral processing

Q19. Which guideline or regulation most directly influences IR instrument validation in pharmaceuticals?

• Good Manufacturing Practice (GMP) and ICH guidelines
• Occupational Safety and Health Administration (OSHA)
• Environmental Protection Agency (EPA)
• Food safety HACCP only

Correct Answer: Good Manufacturing Practice (GMP) and ICH guidelines

Q20. When preparing a KBr pellet for IR, which precaution is critical for good spectra?

• Use moist KBr to improve binding
• Ensure KBr is dry and free of water
• Only use colored KBr
• Press pellets without vacuum

Correct Answer: Ensure KBr is dry and free of water

Q21. Which spectral processing step is commonly applied after acquisition for quantitative IR analysis?

• Baseline correction and normalization
• Changing the interferometer arm length
• Replacing the detector electronically
• Altering the sample chemical structure

Correct Answer: Baseline correction and normalization

Q22. A sudden increase in noise level during scans most likely indicates:

• Improved instrument calibration
• Detector malfunction, electronic noise, or source instability
• Correct baseline alignment
• High-quality polystyrene standard

Correct Answer: Detector malfunction, electronic noise, or source instability

Q23. Which parameter is checked during Performance Qualification (PQ) of an IR spectrophotometer?

• Only instrument installation details
• Consistent analytical performance with real samples
• Manufacturer shipping paperwork
• Laboratory room color

Correct Answer: Consistent analytical performance with real samples

Q24. Linearity testing in IR quantitative methods assesses:

• Relationship between concentration and absorbance/transmittance
• Wavelength calibration accuracy only
• Sample pellet hardness
• Temperature stability of the lab

Correct Answer: Relationship between concentration and absorbance/transmittance

Q25. Which error would most directly shift peak positions in an IR spectrum?

• Improper baseline correction
• Wavelength calibration error or interferometer misalignment
• Low detector gain only
• Using an ATR crystal

Correct Answer: Wavelength calibration error or interferometer misalignment

Q26. Software spectral libraries assist calibration by:

• Replacing the need for instrument qualification
• Providing reference spectra for identification and matching
• Increasing detector cooling speed
• Changing KBr pellet composition

Correct Answer: Providing reference spectra for identification and matching

Q27. Which is a recommended frequency for routine performance verification in a busy QC lab?

• Never verify after initial qualification
• Daily or weekly checks depending on workload and criticality
• Only once a year
• Only when the instrument fails

Correct Answer: Daily or weekly checks depending on workload and criticality

Q28. What is the effect of using an incorrect resolution setting when comparing spectra?

• No effect on peak shapes or positions
• Differences in peak sharpness and potential mismatches with reference spectra
• Automatically improves signal-to-noise
• Makes the instrument immune to stray light

Correct Answer: Differences in peak sharpness and potential mismatches with reference spectra

Q29. Which calibration activity documents are essential for regulatory audits?

• Only verbal assurances from staff
• Calibration certificates, SOPs, IQ/OQ/PQ records, and maintenance logs
• Personal notes with no dates
• Samples of unrelated instruments

Correct Answer: Calibration certificates, SOPs, IQ/OQ/PQ records, and maintenance logs

Q30. In quantitative IR method validation, specificity is demonstrated by:

• Showing linear response only
• Proving the method can distinguish analyte peaks from excipients and interferences
• Using only distilled water as a standard
• Measuring instrument noise alone

Correct Answer: Proving the method can distinguish analyte peaks from excipients and interferences

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