UV–Visible spectroscopy is a core analytical technique for B. Pharm students that probes electronic transitions in drug molecules to yield absorption spectra used in qualitative and quantitative pharmaceutical analysis. This introduction covers key keywords such as chromophores, auxochromes, Beer–Lambert law, molar absorptivity, wavelength selection, π→π* and n→π* transitions, solvent and pH effects, instrumental factors (monochromator, detectors, stray light), and spectral interpretation for assay development, stability testing and impurity profiling. Understanding band assignments, spectral shifts (bathochromic/hypsochromic, hyperchromic/hypochromic) and practical limits enhances method development and validation in pharmaceutical laboratories. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What physical phenomenon does UV–Visible spectroscopy primarily measure?
- Vibrational transitions within molecules
- Electronic transitions between molecular energy levels
- Nuclear spin transitions
- Mass-to-charge ratios of ions
Correct Answer: Electronic transitions between molecular energy levels
Q2. Which expression correctly represents the Beer–Lambert law?
- A = ε + l + c
- A = εlc
- A = l / (εc)
- A = ε / (l c)
Correct Answer: A = εlc
Q3. What are the usual units of the molar absorptivity (ε)?
- cm
- mol L
- M⁻¹ cm⁻¹
- W m⁻²
Correct Answer: M⁻¹ cm⁻¹
Q4. Which electronic transition generally occurs at a shorter wavelength (higher energy)?
- n→π*
- π→π*
- Triplet→Singlet
- Charge-transfer
Correct Answer: π→π*
Q5. A bathochromic shift refers to which change in the absorption spectrum?
- Shift to shorter wavelength (blue shift)
- Shift to longer wavelength (red shift)
- Decrease in peak intensity
- Disappearance of a peak
Correct Answer: Shift to longer wavelength (red shift)
Q6. A hypsochromic shift describes which spectral change?
- Increase in absorbance at λmax
- Shift to longer wavelength
- Shift to shorter wavelength
- Broadening of the absorption band
Correct Answer: Shift to shorter wavelength
Q7. What does a hyperchromic effect indicate in a UV spectrum?
- Decrease in molar absorptivity
- Increase in absorbance intensity
- Shift to shorter wavelengths
- Loss of peak structure
Correct Answer: Increase in absorbance intensity
Q8. How does increasing solvent polarity typically affect n→π* transitions?
- Causes a hypsochromic (blue) shift
- No effect on n→π* transitions
- Causes a bathochromic (red) shift
- Eliminates the absorption band
Correct Answer: Causes a bathochromic (red) shift
Q9. Which cuvette material is most appropriate for measurements below 300–350 nm?
- Borosilicate glass
- Quartz
- Polystyrene
- Polypropylene
Correct Answer: Quartz
Q10. According to the Beer–Lambert law, how does absorbance change if path length is doubled (same concentration)?
- It remains the same
- It doubles
- It halves
- It becomes zero
Correct Answer: It doubles
Q11. What is the primary effect of stray light in a UV–Vis spectrophotometer?
- It causes measured absorbance to be lower than true value at high absorbance
- It increases the molar absorptivity
- It shifts λmax to longer wavelengths
- It only affects fluorescence measurements
Correct Answer: It causes measured absorbance to be lower than true value at high absorbance
Q12. What is a main advantage of a double-beam spectrophotometer over single-beam?
- Cheaper cost
- Smaller size
- Better compensation for source fluctuations and baseline drift
- Higher sample throughput without standards
Correct Answer: Better compensation for source fluctuations and baseline drift
Q13. Which of the following is NOT typically a chromophore in organic drug molecules?
- Aromatic ring
- Conjugated diene
- Carbonyl group
- Saturated alkane chain with no unsaturation
Correct Answer: Saturated alkane chain with no unsaturation
Q14. Which type of electronic transition is spin-forbidden?
- Singlet → Singlet transition
- Singlet → Triplet transition
- π→π* transition within same multiplicity
- n→π* singlet transition
Correct Answer: Singlet → Triplet transition
Q15. What does a high molar absorptivity (ε) for a band indicate?
- Low probability of the electronic transition
- High probability (strong intensity) of the electronic transition
- Large sample volume required
- That the band is due to vibrational transitions only
Correct Answer: High probability (strong intensity) of the electronic transition
Q16. How are photon energy (E) and wavelength (λ) related?
- E is directly proportional to λ
- E is inversely proportional to λ (E = hc/λ)
- E is independent of λ
- E equals λ squared
Correct Answer: E is inversely proportional to λ (E = hc/λ)
Q17. Which factor commonly causes deviation from linearity in Beer–Lambert behavior at high concentration?
- Instrument detector type
- Cuvette color
- Molecular interactions (association, dissociation, refractive index change) at high concentration
- Using monochromatic light
Correct Answer: Molecular interactions (association, dissociation, refractive index change) at high concentration
Q18. Which spectral technique can improve resolution of overlapping UV bands for quantitative analysis?
- First or higher-order derivative spectroscopy
- Thin-layer chromatography
- Mass spectrometry
- Polarimetry
Correct Answer: First or higher-order derivative spectroscopy
Q19. Which characteristic best describes a charge-transfer absorption band?
- Narrow and weak
- Very sharp vibrational fine structure
- Broad and intense, often at longer wavelengths
- Only observed in gaseous samples
Correct Answer: Broad and intense, often at longer wavelengths
Q20. Which component of a UV–Vis spectrometer disperses polychromatic light into its spectral components?
- Light source
- Monochromator (prism or diffraction grating)
- Sample holder
- Detector
Correct Answer: Monochromator (prism or diffraction grating)
Q21. Which modern detector provides simultaneous acquisition of many wavelengths in UV–Vis spectrometry?
- Photomultiplier tube (PMT)
- Photodiode array (PDA)
- Thermocouple detector
- Ionization chamber
Correct Answer: Photodiode array (PDA)
Q22. The Franck–Condon principle explains which aspect of electronic transitions?
- Electronic transitions occur with change in spin multiplicity only
- Electronic transitions are slow compared to nuclear motion
- Electronic transitions are essentially vertical; nuclear positions do not change instantaneously
- Only rotational levels are involved
Correct Answer: Electronic transitions are essentially vertical; nuclear positions do not change instantaneously
Q23. Under which condition is vibrational fine structure in an electronic band most likely to be resolved?
- High temperature and broad solvent bands
- Low temperature and rigid environment (reduced broadening)
- Very concentrated solution with scattering
- Using visible light only
Correct Answer: Low temperature and rigid environment (reduced broadening)
Q24. How does ionization of a drug molecule (pH change) commonly affect its UV spectrum?
- No effect on λmax or absorptivity
- Only shifts peaks to the UV-C region
- Can change λmax and molar absorptivity due to altered electronic structure
- Makes the molecule fluorescent
Correct Answer: Can change λmax and molar absorptivity due to altered electronic structure
Q25. Why is derivatization used in UV–Vis analysis of some pharmaceuticals?
- To remove chromophores
- To increase volatility for GC analysis
- To introduce or enhance a chromophore for better sensitivity/selectivity
- To decrease molecular weight
Correct Answer: To introduce or enhance a chromophore for better sensitivity/selectivity
Q26. What does the additivity of absorbance mean for a mixture of non-interacting species?
- Total absorbance equals the product of individual absorbances
- Total absorbance equals the sum of individual absorbances at a given wavelength
- Each component’s absorbance is independent of concentration
- Absorbance cannot be used for mixtures
Correct Answer: Total absorbance equals the sum of individual absorbances at a given wavelength
Q27. Which statement is NOT true regarding the Beer–Lambert law?
- It requires monochromatic light or narrow bandpass
- It is valid only for non-scattering, homogeneous solutions
- Absorbance is independent of path length
- High concentrations can cause deviations from linearity
Correct Answer: Absorbance is independent of path length
Q28. Which factor commonly contributes to instrumental peak broadening in UV–Vis spectra?
- Very narrow monochromator slit width
- Large instrumental bandpass (wide slit width)
- Perfectly monochromatic radiation
- Use of a vacuum cuvette
Correct Answer: Large instrumental bandpass (wide slit width)
Q29. When selecting an analytical wavelength for a drug assay, which is generally the best choice?
- Wavelength at which absorbance is zero
- Wavelength of maximum absorbance (λmax) provided no interference
- Shortest possible wavelength in the instrument range
- Wavelength where solvent absorbs strongly
Correct Answer: Wavelength of maximum absorbance (λmax) provided no interference
Q30. Which change will generally lower the limit of detection (LOD) in UV–Vis quantitation?
- Increasing baseline noise
- Decreasing molar absorptivity of the analyte
- Increasing slope (sensitivity) and decreasing baseline noise
- Using a shorter path length
Correct Answer: Increasing slope (sensitivity) and decreasing baseline noise
I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.
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