Spectroscopy in phytochemical analysis MCQs With Answer

Spectroscopy in phytochemical analysis MCQs With Answer

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Spectroscopy in phytochemical analysis MCQs With Answer

Spectroscopy is essential for phytochemical analysis in B.Pharm programs, combining techniques like UV-Vis, IR (FTIR), NMR, and mass spectrometry (MS) to identify and quantify plant-derived compounds. This introduction highlights structural elucidation, functional group identification, hyphenated techniques (LC-MS, GC-MS), sample preparation, derivatization, and quantitative concepts such as Beer–Lambert law, detection limits, and calibration. Emphasis on spectral interpretation for alkaloids, flavonoids, terpenes, and glycosides prepares students for practical analysis and research. Mastery of spectroscopy accelerates drug discovery, quality control, and herbal standardization in pharmaceutical practice. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which spectroscopic technique is most suitable for determining the molecular weight and fragmentation pattern of a phytochemical?

  • UV-Visible spectroscopy
  • Infrared (FTIR) spectroscopy
  • Mass spectrometry (MS)
  • Proton NMR (1H NMR)

Correct Answer: Mass spectrometry (MS)

Q2. According to Beer–Lambert law, which parameter is directly proportional to absorbance at a fixed wavelength?

  • Path length and concentration
  • Wavelength and solvent polarity
  • Instrument noise
  • Molar mass

Correct Answer: Path length and concentration

Q3. A strong, sharp IR absorption around 1700 cm−1 typically indicates which functional group in a phytochemical?

  • Alcohol O–H
  • Carbonyl C=O
  • Alkene C=C
  • Nitro NO2

Correct Answer: Carbonyl C=O

Q4. Which NMR technique is most useful to determine the number of chemically distinct carbon atoms in a compound?

  • 1H NMR
  • 13C NMR
  • UV-Vis spectroscopy
  • FTIR

Correct Answer: 13C NMR

Q5. In 1H NMR, a multiplet integrating to three protons near δ 0.9 ppm is most likely due to which group?

  • Aromatic protons
  • Methyl group (CH3) adjacent to aliphatic chain
  • Aldehyde proton
  • Hydroxyl proton

Correct Answer: Methyl group (CH3) adjacent to aliphatic chain

Q6. Which hyphenated technique is best for analyzing thermally unstable, nonvolatile plant glycosides?

  • GC-MS without derivatization
  • LC-MS (e.g., HPLC-ESI-MS)
  • IR spectroscopy
  • Flame photometry

Correct Answer: LC-MS (e.g., HPLC-ESI-MS)

Q7. Which ionization method is soft and commonly used in LC-MS for polar phytochemicals?

  • Electron ionization (EI)
  • Electrospray ionization (ESI)
  • Fast atom bombardment (FAB)
  • MALDI for volatile analytes

Correct Answer: Electrospray ionization (ESI)

Q8. In mass spectrometry, the peak with highest intensity is called the:

  • Parent ion
  • Base peak
  • Isotopic peak
  • Fragment ion

Correct Answer: Base peak

Q9. Which IR region is referred to as the “fingerprint region” and is useful for identifying phytochemical-specific patterns?

  • 4000–2500 cm−1
  • 2500–2000 cm−1
  • 2000–1500 cm−1
  • 1500–500 cm−1

Correct Answer: 1500–500 cm−1

Q10. A bathochromic shift in UV-Vis spectroscopy indicates which change?

  • Shift to shorter wavelength (hypsochromic)
  • Shift to longer wavelength (red shift)
  • No change in conjugation
  • Decrease in molar absorptivity

Correct Answer: Shift to longer wavelength (red shift)

Q11. Which spectral feature helps distinguish flavonoid aglycones from flavonoid glycosides in UV-Vis?

  • Presence of two major absorption bands (Band I and II) with shifts due to glycosylation
  • Strong C–H stretching at 3000 cm−1
  • Characteristic M+ peak at m/z 18
  • Distinct 13C NMR signal at δ 200 ppm

Correct Answer: Presence of two major absorption bands (Band I and II) with shifts due to glycosylation

Q12. Which derivatization is commonly performed prior to GC-MS analysis of plant sugars or steroids?

  • Acetylation or silylation (e.g., TMS derivatization)
  • Direct injection without treatment
  • Protonation for LC-MS
  • Reduction with sodium borohydride for LC-UV

Correct Answer: Acetylation or silylation (e.g., TMS derivatization)

Q13. In 13C NMR, which technique helps distinguish CH, CH2, and CH3 carbons?

  • DEPT (Distortionless Enhancement by Polarization Transfer)
  • IR fingerprinting
  • UV-Vis absorbance
  • Mass spectral fragmentation

Correct Answer: DEPT (Distortionless Enhancement by Polarization Transfer)

Q14. Which isotopic pattern in mass spectra suggests the presence of a bromine atom?

  • A single peak only
  • Two peaks of nearly equal intensity separated by 2 m/z units
  • Multiple peaks separated by 1 m/z repeatedly
  • High intensity at m/z 18

Correct Answer: Two peaks of nearly equal intensity separated by 2 m/z units

Q15. ATR-FTIR is especially useful for phytochemical analysis because it allows:

  • Complex sample vaporization
  • Direct analysis of solids, pastes, and films with minimal prep
  • Quantitative NMR measurements
  • High-resolution mass determination

Correct Answer: Direct analysis of solids, pastes, and films with minimal prep

Q16. Which parameter in LC-MS influences chromatographic retention and ionization efficiency of phytochemicals?

  • Column temperature only
  • Mobile phase composition (organic modifier and pH)
  • FTIR resolution
  • Molar mass of detector lamp

Correct Answer: Mobile phase composition (organic modifier and pH)

Q17. A characteristic 1H NMR signal at δ 9–10 ppm usually corresponds to which proton type in phytochemicals?

  • Aliphatic methyl protons
  • Aromatic protons
  • Aldehyde proton
  • Exchangeable hydroxyl proton only

Correct Answer: Aldehyde proton

Q18. High-resolution mass spectrometry (HRMS) is most valuable in phytochemical analysis for:

  • Measuring UV absorbance accurately
  • Determining exact mass to deduce molecular formula
  • Recording IR fingerprint patterns
  • Measuring coupling constants in NMR

Correct Answer: Determining exact mass to deduce molecular formula

Q19. Which fragmentation in EI mass spectrometry commonly corresponds to loss of a sugar moiety (162 Da) from a glycoside?

  • Loss of H2O (18 Da)
  • Loss of a hexose unit (~162 Da)
  • Loss of CO2 (44 Da)
  • Gain of proton

Correct Answer: Loss of a hexose unit (~162 Da)

Q20. Which NMR parameter gives information about the number of neighboring protons?

  • Chemical shift only
  • Multiplicity (splitting pattern) and coupling constants (J values)
  • Mass-to-charge ratio
  • IR transmittance

Correct Answer: Multiplicity (splitting pattern) and coupling constants (J values)

Q21. Which spectral technique best differentiates isomeric phytochemicals that have identical molecular weights?

  • Low-resolution MS only
  • NMR spectroscopy (1H and 13C) and MS/MS fragmentation
  • UV-Vis without chromatography
  • Simple TLC visualization under UV

Correct Answer: NMR spectroscopy (1H and 13C) and MS/MS fragmentation

Q22. In UV-Vis, molar absorptivity (ε) is used to:

  • Calculate sample viscosity
  • Determine intensity of IR bands
  • Relate absorbance to concentration for quantitation
  • Measure mass fragmentation

Correct Answer: Relate absorbance to concentration for quantitation

Q23. Which technique provides direct evidence of hydrogen bonding and OH groups by broad absorptions?

  • 13C NMR
  • FTIR spectroscopy showing broad O–H stretch around 3200–3600 cm−1
  • Mass spectrometry
  • UV-Vis Band II only

Correct Answer: FTIR spectroscopy showing broad O–H stretch around 3200–3600 cm−1

Q24. Which GC-MS ionization method is most commonly used for small volatile phytochemicals and produces extensive fragmentation?

  • Electrospray ionization (ESI)
  • Electron ionization (EI)
  • APCI in LC-MS
  • MALDI for small volatiles

Correct Answer: Electron ionization (EI)

Q25. Which spectroscopic change indicates conjugation extension in a phytochemical molecule?

  • Hypsochromic shift in UV-Vis
  • Bathochromic shift and increased molar absorptivity in UV-Vis
  • Loss of IR carbonyl band
  • Disappearance of mass spectral molecular ion

Correct Answer: Bathochromic shift and increased molar absorptivity in UV-Vis

Q26. For quantitation of a marker compound in herbal extract by HPLC-UV, which is essential?

  • Calibration curve using standards and appropriate wavelength
  • Only MS detection without standards
  • Visual comparison to a TLC spot
  • IR fingerprint comparison

Correct Answer: Calibration curve using standards and appropriate wavelength

Q27. Which NMR technique allows observation of through-bond correlations between 1H and 13C to assign connectivity?

  • IR spectroscopy
  • HSQC and HMBC 2D NMR experiments
  • GC-MS
  • UV-Vis

Correct Answer: HSQC and HMBC 2D NMR experiments

Q28. In phytochemical MS analysis, what does tandem MS/MS provide?

  • Only molecular weight without structural info
  • Fragmentation patterns of selected precursor ions for structural elucidation
  • IR fingerprints
  • UV absorption maxima

Correct Answer: Fragmentation patterns of selected precursor ions for structural elucidation

Q29. Which instrumental factor improves sensitivity for low-abundance phytochemicals in LC-MS?

  • Using a detector at random wavelength
  • Optimizing ion source parameters and using selected ion monitoring (SIM) or SRM
  • Decreasing column efficiency
  • Removing the mobile phase modifier

Correct Answer: Optimizing ion source parameters and using selected ion monitoring (SIM) or SRM

Q30. Which combination is most effective for comprehensive phytochemical profiling (qualitative + quantitative)?

  • TLC and melting point only
  • HPLC-UV for quantitation combined with LC-MS/MS and NMR for structural identification
  • FTIR only
  • Visual color tests alone

Correct Answer: HPLC-UV for quantitation combined with LC-MS/MS and NMR for structural identification

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