Impurity Profiling: Method development, forced degradation and degradant characterization MCQs With Answer

Introduction:

Impurity profiling is a critical component of drug development and regulatory submission. This set of MCQs focuses on method development, forced degradation studies, and degradant characterization—key topics in the MPA 102T Advanced Pharmaceutical Analysis syllabus. The questions encourage understanding of stability‑indicating method design, appropriate stress conditions, analytical techniques used for detection and structural elucidation (LC‑MS, HRMS, NMR, PDA), and interpretation of mass balance and peak purity. These practice items are aimed at strengthening conceptual clarity and practical decision‑making for M.Pharm students preparing for exams and real‑world impurity investigations.

Q1. Which of the following best describes the primary purpose of a forced degradation study during method development?

• To accelerate the shelf life of the commercial product
• To generate potential degradation products and demonstrate a stability‑indicating method
• To determine the exact shelf life under normal storage conditions
• To replace chronic toxicity testing for degradants

Correct Answer: To generate potential degradation products and demonstrate a stability‑indicating method

Q2. When designing a stability‑indicating chromatographic method, which attribute is most critical to ensure degradants are detected separately from the API?

• Short total run time
• High column temperature
• Resolution between API and degradant peaks
• Using a single wavelength detection

Correct Answer: Resolution between API and degradant peaks

Q3. Which stress condition is LEAST likely to induce oxidation-related degradants?

• Exposure to hydrogen peroxide solution
• Storage in presence of light (photolysis)
• Inclusion of trace transition metal catalysts
• Heating in sealed inert atmosphere (nitrogen)

Correct Answer: Heating in sealed inert atmosphere (nitrogen)

Q4. Which analytical technique provides the most definitive structural information for an unknown degradant once purified?

• Ultra violet-visible spectrophotometry (UV‑Vis)
• High resolution mass spectrometry (HRMS) combined with nuclear magnetic resonance (NMR)
• Infrared spectroscopy (IR) alone
• Thin layer chromatography (TLC)

Correct Answer: High resolution mass spectrometry (HRMS) combined with nuclear magnetic resonance (NMR)

Q5. In forced degradation studies, what is the usual target amount of API degradation to generate degradants without extensive secondary reactions?

• 0–1% degradation
• 5–20% degradation
• 50–80% degradation
• 100% degradation

Correct Answer: 5–20% degradation

Q6. Which approach is most appropriate to assess peak purity of an API peak in stress samples?

• Single‑wavelength HPLC detection only
• Peak area comparison with a reference standard without spectral data
• Photodiode array (PDA) spectral comparison and orthogonal method confirmation
• Rely solely on retention time match with standard

Correct Answer: Photodiode array (PDA) spectral comparison and orthogonal method confirmation

Q7. During method validation for an impurity assay, which parameter demonstrates the method can specifically quantify the API in presence of degradants?

• Linearity
• Accuracy
• Specificity
• Precision

Correct Answer: Specificity

Q8. Which sample preparation strategy is commonly used to isolate degradants for structural characterization after forced degradation?

• Direct injection of crude stressed sample into NMR without cleanup
• Preparative LC fraction collection followed by solvent removal and concentration
• Dilution with water and immediate MS analysis
• Filtration through 0.45 µm membrane only

Correct Answer: Preparative LC fraction collection followed by solvent removal and concentration

Q9. What is the primary advantage of high‑resolution MS (HRMS) over nominal mass MS in degradant identification?

• Lower instrument cost
• Faster run times for all samples
• Accurate mass measurement enabling elemental composition determination
• No need for chromatographic separation

Correct Answer: Accurate mass measurement enabling elemental composition determination

Q10. In a forced degradation experiment, which control improves confidence that observed degradants arise from chemical stress rather than sample handling?

• Running only one stress condition and no replicates
• Using time‑zero (untreated) and vehicle controls processed identically
• Heating the sample without a blank
• Mixing stressed samples from different conditions together

Correct Answer: Using time‑zero (untreated) and vehicle controls processed identically

Q11. Which factor is most important when choosing a chromatographic column for impurity profiling of a moderately polar drug?

• Column brand name only
• Stationary phase chemistry and selectivity for separating structurally related impurities
• Color of the column hardware
• Pore size irrelevant for small molecules

Correct Answer: Stationary phase chemistry and selectivity for separating structurally related impurities

Q12. What does a mass balance significantly lower than 100% typically indicate in forced degradation studies?

• Perfect method performance
• Loss of volatile degradants, sample adsorption, or undetected degradation products
• That the API concentration was too high
• That the instrument calibration is unnecessary

Correct Answer: Loss of volatile degradants, sample adsorption, or undetected degradation products

Q13. Which of the following best describes the term “stability‑indicating method”?

• An assay that quantifies only the placebo matrix
• An analytical procedure that accurately measures the active ingredient without interference from degradants, impurities, or excipients
• A method used solely for dissolution testing
• An unstable chromatographic method intentionally

Correct Answer: An analytical procedure that accurately measures the active ingredient without interference from degradants, impurities, or excipients

Q14. During LC‑MS analysis of degradants, which ionization technique is generally preferred for polar, thermally labile pharmaceutical degradants?

• Electron impact (EI) ionization
• Electrospray ionization (ESI)
• Field ionization (FI)
• Thermal desorption

Correct Answer: Electrospray ionization (ESI)

Q15. What is the first analytical step when a new unknown peak appears in long‑term stability samples?

• Immediately publish safety data
• Confirm peak is not a system artifact and check peak purity and retention behavior
• Discard the batch
• Ignore it if below a certain numeric threshold without investigation

Correct Answer: Confirm peak is not a system artifact and check peak purity and retention behavior

Q16. Which of the following is a recommended practice when reporting degradants in regulatory submissions?

• Report only degradants above 10% and ignore lower ones
• Provide identity, formation pathway, levels over time, and qualification/toxicology data if required
• Only include chromatograms without any structural data
• Use non‑validated methods for quantitation in submission

Correct Answer: Provide identity, formation pathway, levels over time, and qualification/toxicology data if required

Q17. Which fragmentation data is most useful for proposing a tentative structure of a degradant in LC‑MS/MS?

• Retention time only
• Product ion spectrum showing characteristic fragment ions and neutral losses
• UV absorbance at 210 nm alone
• Sample color

Correct Answer: Product ion spectrum showing characteristic fragment ions and neutral losses

Q18. Why are orthogonal analytical methods recommended during degradant characterization?

• To increase analysis time unnecessarily
• To confirm results using different physical/chemical principles, reducing false identifications
• To hide contradictory data
• Because regulations mandate using at least five methods

Correct Answer: To confirm results using different physical/chemical principles, reducing false identifications

Q19. Which of the following indicates a chromatographic method may not be stability‑indicating?

• Well separated API and impurities in stressed samples
• Co‑elution of API with a degradant peak confirmed by PDA or MS
• Consistent retention times and linearity for standards
• Good precision and accuracy for impurity spiking experiments

Correct Answer: Co‑elution of API with a degradant peak confirmed by PDA or MS

Q20. When a degradant is observed only under photolytic stress, what is the most likely conclusion?

• The degradant is formed primarily by hydrolysis
• The degradant is photolabile and light exposure control is needed in formulation and packaging
• The degradant is inert and requires no further action
• Thermal stability studies are unnecessary

Correct Answer: The degradant is photolabile and light exposure control is needed in formulation and packaging

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