Introduction: UV–Visible spectroscopy (UV-Vis) is an essential tool in pharmaceutical analysis for qualitative and quantitative determination of drugs. This technique relies on the Beer-Lambert law, absorbance at characteristic λmax, and parameters like molar absorptivity and path length to perform accurate single-component assays and robust multicomponent analysis. In pharmaceuticals, methods such as the simultaneous equation method, derivative spectrophotometry, ratio spectra and multivariate calibration enable resolution of overlapping spectra in combined formulations. Understanding sample preparation, solvent effects, linearity, sensitivity (LOD/LOQ), and method validation is crucial for reliable UV-Vis assays. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What fundamental law relates absorbance to concentration in UV–Visible spectroscopy?
- Beer-Lambert law
- Fick’s law
- Henry’s law
- Hooke’s law
Correct Answer: Beer-Lambert law
Q2. In single-component analysis by UV-Vis, the wavelength of maximum absorbance is referred to as:
- Isoelectric point
- λmax
- Chromatographic peak
- Retention time
Correct Answer: λmax
Q3. Which parameter expresses how strongly a compound absorbs light at a given wavelength?
- pKa
- Molar absorptivity (ε)
- Retention factor (Rf)
- Viscosity
Correct Answer: Molar absorptivity (ε)
Q4. When two components in a mixture absorb at overlapping wavelengths, which UV-Vis method can resolve their concentrations?
- Simultaneous equation method
- Distillation
- Gravimetric analysis
- pH titration
Correct Answer: Simultaneous equation method
Q5. In the simultaneous equation method for two components A and B, what two measurements are required?
- Absorbances at two selected wavelengths
- Masses of A and B
- Retention times in HPLC
- pH and temperature
Correct Answer: Absorbances at two selected wavelengths
Q6. Which technique enhances resolution of overlapping spectra by computing first or higher derivatives of the absorption spectrum?
- Derivative spectrophotometry
- Fluorimetry
- Mass spectrometry
- NMR spectroscopy
Correct Answer: Derivative spectrophotometry
Q7. What is the significance of an isosbestic point in a binary mixture?
- Absorbance is independent of the relative concentrations of the two species
- It indicates pH instability
- It marks the chromatographic retention time
- It is used to measure viscosity
Correct Answer: Absorbance is independent of the relative concentrations of the two species
Q8. Which factor does NOT directly affect absorbance in UV-Vis measurements?
- Path length of the cuvette
- Concentration of analyte
- Molar absorptivity
- Magnetic field strength
Correct Answer: Magnetic field strength
Q9. The absorbance additivity principle states that:
- Total absorbance equals the sum of individual component absorbances at a given wavelength
- Absorbance multiplies for mixtures
- Only the most absorbing species contributes
- Absorbance is independent of concentration
Correct Answer: Total absorbance equals the sum of individual component absorbances at a given wavelength
Q10. Which solvent parameter can significantly shift λmax of a drug during UV-Vis analysis?
- Dielectric constant (solvent polarity)
- Magnetic susceptibility
- Boiling point of solvent
- Density of container glass
Correct Answer: Dielectric constant (solvent polarity)
Q11. For method validation in UV-Vis assays, which parameter assesses the smallest reliably detectable concentration?
- Limit of detection (LOD)
- Linearity range
- Precision
- Specificity
Correct Answer: Limit of detection (LOD)
Q12. Which approach uses a ratio of absorbances at two wavelengths to quantify a component in a mixture?
- Q-analysis (absorbance ratio method)
- Gravimetric titration
- Thermogravimetry
- Conductometry
Correct Answer: Q-analysis (absorbance ratio method)
Q13. In multicomponent UV-Vis analysis, multivariate calibration (e.g., PLS) is advantageous because it:
- Handles highly overlapping spectra and correlates many wavelengths simultaneously
- Requires no instrument calibration
- Eliminates the need for standards
- Operates only at single wavelength
Correct Answer: Handles highly overlapping spectra and correlates many wavelengths simultaneously
Q14. Which instrumental parameter determines spectral resolution and influences peak shape?
- Slit width
- Sample viscosity
- Laboratory humidity
- Manufacturer logo
Correct Answer: Slit width
Q15. When constructing a calibration curve for a single component, which plot is most common?
- Absorbance versus concentration
- Time versus temperature
- Mass versus volume
- pH versus conductivity
Correct Answer: Absorbance versus concentration
Q16. Which of the following is a common interference in UV-Vis pharmaceutical assays?
- Excipients that absorb at similar wavelengths
- Ambient sound
- Colour of the laboratory bench
- Time of day
Correct Answer: Excipients that absorb at similar wavelengths
Q17. Ratio spectra derivative spectrophotometry is used primarily to:
- Resolve overlapping signals in binary and ternary mixtures
- Measure boiling points
- Separate enantiomers
- Sterilize samples
Correct Answer: Resolve overlapping signals in binary and ternary mixtures
Q18. For a fixed path length, doubling the concentration of an absorbing species will:
- Double the absorbance (within linear range)
- Halve the absorbance
- Increase absorbance by four times
- Have no effect on absorbance
Correct Answer: Double the absorbance (within linear range)
Q19. What is the main purpose of using a blank in UV-Vis measurements?
- To correct for solvent and cuvette absorbance
- To increase instrument throughput
- To sterilize the spectrophotometer
- To calibrate temperature
Correct Answer: To correct for solvent and cuvette absorbance
Q20. Which quality parameter evaluates closeness of measured values to the true value in UV-Vis assays?
- Accuracy
- Repeatability
- Robustness
- Sensitivity
Correct Answer: Accuracy
Q21. When selecting wavelengths for simultaneous equation method, you should choose wavelengths where:
- Each analyte has significant and differing absorbance contributions
- Both analytes have zero absorbance
- Only one analyte absorbs at both wavelengths
- The solvent absorbs maximally
Correct Answer: Each analyte has significant and differing absorbance contributions
Q22. What is the effect of stray light on UV-Vis measurements?
- It causes deviation from linearity at high absorbance values
- It increases sample concentration
- It reduces solvent polarity
- It stabilizes λmax
Correct Answer: It causes deviation from linearity at high absorbance values
Q23. Which sample handling practice improves accuracy of UV-Vis assays?
- Using matched cuvettes and consistent path length
- Changing cuvettes between each measurement without rinsing
- Using colored cuvettes to mask impurities
- Measuring without blanks
Correct Answer: Using matched cuvettes and consistent path length
Q24. In a ternary mixture, which UV-Vis approach can help quantify three overlapping components?
- Multivariate calibration or multi-wavelength methods
- Single-point titration
- Paper chromatography
- Simple dilution without measurement
Correct Answer: Multivariate calibration or multi-wavelength methods
Q25. Which pharmacopoeial requirement is commonly assessed for UV-Vis analytical methods?
- System suitability, linearity, accuracy, precision, specificity
- Boiling point range only
- Colour of reagent bottles
- Manufacturer’s logo compliance
Correct Answer: System suitability, linearity, accuracy, precision, specificity
Q26. The term “specificity” in UV-Vis method validation means:
- The method can measure the analyte in presence of other components
- The method is cheap
- The method uses the latest instrument
- The method is complicated
Correct Answer: The method can measure the analyte in presence of other components
Q27. When would you apply baseline correction during spectral acquisition?
- To remove background drift and instrument noise
- To increase sample concentration
- To change the chemical structure
- To adjust sample pH
Correct Answer: To remove background drift and instrument noise
Q28. What does a high molar absorptivity (ε) indicate about an analyte?
- It has strong absorbance per molar concentration and is highly sensitive in UV-Vis
- It has low solubility
- It is nonpolar
- It is volatile
Correct Answer: It has strong absorbance per molar concentration and is highly sensitive in UV-Vis
Q29. Which practice helps minimize matrix effects in multicomponent UV-Vis assays of formulations?
- Appropriate sample dilution, extraction, and use of matched placebos
- Measuring undiluted suspensions without filtration
- Using tap water as solvent
- Avoiding use of standards
Correct Answer: Appropriate sample dilution, extraction, and use of matched placebos
Q30. Which statement best describes the use of UV-Vis spectroscopy in pharmaceutical quality control?
- It provides rapid, cost-effective assays for drug identity, assay, and dissolution when properly validated
- It always replaces HPLC in all assays
- It cannot be used for multicomponent formulations
- It is unsuitable for routine analysis
Correct Answer: It provides rapid, cost-effective assays for drug identity, assay, and dissolution when properly validated
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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