Introduction to UV–Visible spectroscopy MCQs With Answer

Introduction to UV–Visible Spectroscopy MCQs With Answers

UV–Visible spectroscopy is a foundational tool in Modern Pharmaceutical Analytical Techniques, enabling rapid, non-destructive quantification and characterization of drug molecules. For M. Pharm students, a strong grasp of Beer–Lambert law, instrumentation, solvent effects, spectral shifts, and method validation is essential for designing robust assays and interpreting spectra in qualitative and quantitative analyses. This MCQ set deepens understanding of core principles, including chromophores and auxochromes, detector choices, isosbestic points, stray light, slit width, path length, and matrix effects. Each question is crafted to reflect real-world analytical considerations encountered in pharma R&D and QC, helping you connect theory with practice and build confidence for examinations and laboratory applications.

Q1. Which equation correctly represents the Beer–Lambert law for absorbance in UV–Visible spectroscopy?

• A = ε b c
• A = log10(T)
• A = ε / (b c)
• T = ε b c

Correct Answer: A = ε b c

Q2. What is the typical working wavelength range of a UV–Visible spectrophotometer used in pharmaceutical analysis?

• 190–800 nm
• 100–400 nm
• 400–1100 nm
• 10–100 nm

Correct Answer: 190–800 nm

Q3. Which light source combination is most appropriate in a double-beam UV–Visible spectrophotometer?

• Deuterium lamp for UV and tungsten–halogen lamp for visible–NIR
• Mercury vapor lamp for UV and xenon flash for visible
• Sodium lamp for visible and Nernst glower for UV
• LED array for UV and carbon arc for visible

Correct Answer: Deuterium lamp for UV and tungsten–halogen lamp for visible–NIR

Q4. For measurements at 220 nm, which cuvette material is most suitable?

• Quartz cuvette
• Glass cuvette
• Plastic (polystyrene) cuvette
• Any cuvette is suitable at 220 nm

Correct Answer: Quartz cuvette

Q5. What are the correct units of molar absorptivity (ε) in Beer–Lambert law?

• L mol⁻¹ cm⁻¹
• mol L⁻¹ cm
• cm² mol⁻¹
• L⁻¹ mol cm⁻¹

Correct Answer: L mol⁻¹ cm⁻¹

Q6. Increasing the monochromator slit width (spectral bandpass) generally has what effect on a UV spectrum?

• Increases signal intensity but decreases spectral resolution
• Decreases signal but improves spectral resolution
• Increases both signal and spectral resolution
• No effect on spectral shape or sensitivity

Correct Answer: Increases signal intensity but decreases spectral resolution

Q7. What is the principal effect of stray light on quantitative UV–Visible measurements?

• Causes apparent absorbance to be lower, giving negative deviation at high absorbance
• Increases apparent absorbance, giving positive deviation at high absorbance
• Sharpens spectral features and improves resolution
• Eliminates the need for a blank measurement

Correct Answer: Causes apparent absorbance to be lower, giving negative deviation at high absorbance

Q8. The presence of an isosbestic point in UV spectra typically indicates:

• Two interconverting species with constant total concentration during a reaction
• Instrument detector saturation at a particular wavelength
• Significant light scattering due to particulates
• Approaching the solvent cutoff in the UV region

Correct Answer: Two interconverting species with constant total concentration during a reaction

Q9. Why is a blank (baseline correction) essential in UV–Visible spectroscopy?

• To compensate for absorbance of solvent and cuvette and to set a proper zero baseline
• To reduce the path length without changing cuvettes
• To increase the molar absorptivity of analytes
• To correct for photobleaching of the analyte

Correct Answer: To compensate for absorbance of solvent and cuvette and to set a proper zero baseline

Q10. For recording a UV spectrum at 200 nm of a poorly water‑soluble drug, which solvent is most appropriate due to a low UV cutoff?

• Acetonitrile
• Ethanol
• Chloroform
• Dimethyl sulfoxide (DMSO)

Correct Answer: Acetonitrile

Q11. Which modification typically produces a bathochromic (red) shift in UV spectra?

• Conjugation increases or an auxochrome like –OH is introduced
• Solvent polarity decreases for π→π* transitions
• Slit width is reduced substantially
• Sample is diluted tenfold

Correct Answer: Conjugation increases or an auxochrome like –OH is introduced

Q12. What is a key advantage of a photodiode array (PDA) detector in UV–Visible spectroscopy?

• Simultaneous acquisition of full spectrum in milliseconds for rapid scans and peak purity
• Highest dark current but best sensitivity among detectors
• Complete immunity to stray light
• Requires monochromator scanning to collect spectra

Correct Answer: Simultaneous acquisition of full spectrum in milliseconds for rapid scans and peak purity

Q13. Compared to single-beam instruments, double-beam spectrophotometers primarily:

• Compensate for source/intensity drift and allow continuous reference correction
• Require smaller sample volumes
• Provide higher spectral resolution
• Eliminate the need for calibration standards

Correct Answer: Compensate for source/intensity drift and allow continuous reference correction

Q14. If the transmittance (T) is 20%, what is the absorbance (A)?

• 0.699
• 0.301
• 0.200
• 1.000

Correct Answer: 0.699

Q15. For routine quantitative UV assays, which absorbance range typically offers optimal precision and linearity?

• 0.2–0.8
• 1.5–2.0
• 0.01–0.05
• 2.5–3.0

Correct Answer: 0.2–0.8

Q16. Which strategy most effectively resolves overlapping UV bands and corrects for baseline drift?

• First- or second-derivative UV spectroscopy to enhance band separation
• Increasing cuvette path length
• Switching to glass cuvettes
• Using a higher concentration to accentuate peaks

Correct Answer: First- or second-derivative UV spectroscopy to enhance band separation

Q17. If concentration and molar absorptivity remain constant, what happens to absorbance when path length doubles from 1 cm to 2 cm?

• Double
• Halve
• Remain unchanged
• Increase logarithmically but less than double

Correct Answer: Double

Q18. Why are buffer solutions commonly used when recording UV spectra of ionizable drugs?

• To fix pH and control ionization, producing reproducible λmax and absorbance
• To increase the solvent cutoff to shorter wavelengths
• To avoid the need for a blank
• To decrease molar absorptivity and prevent saturation

Correct Answer: To fix pH and control ionization, producing reproducible λmax and absorbance

Q19. How does turbidity or particulate matter affect UV–Visible measurements?

• Light scattering elevates baseline and distorts absorbance; samples should be filtered/centrifuged
• No effect on UV–Visible measurements
• Increases resolution of vibronic fine structure
• Only affects measurements above 600 nm

Correct Answer: Light scattering elevates baseline and distorts absorbance; samples should be filtered/centrifuged

Q20. According to ICH guidelines, how are LOD and LOQ estimated from a UV calibration curve?

• LOD = 3.3 σ/S and LOQ = 10 σ/S, where σ is SD of blank or y-intercepts and S is slope
• LOD = 10 σ/S and LOQ = 3.3 σ/S
• LOD = σ × S and LOQ = 3σ × S
• LOD/LOQ cannot be estimated from UV data

Correct Answer: LOD = 3.3 σ/S and LOQ = 10 σ/S, where σ is SD of blank or y-intercepts and S is slope

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