Sources of impurities in medicinal agents MCQs With Answer

Introduction: Sources of impurities in medicinal agents MCQs With Answer is a focused review for B.Pharm students on pharmaceutical impurities, their origins, detection and control. Understanding sources of impurities—such as synthetic by‑products, degradation products, residual solvents, heavy metals, catalysts, microbial contamination, and packaging leachables—is essential for drug quality, safety and regulatory compliance. This topic links pharmaceutical analysis, quality control, stability studies, and ICH guidelines (Q3A/Q3B/Q3D) to practical testing methods like HPLC, GC, ICP‑MS and microbiological assays. Clear knowledge of impurity sources helps prevent adverse effects and ensures formulation robustness. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the most common source of degradation impurities in stored pharmaceutical tablets?

• Contamination during manufacturing
• Hydrolysis due to moisture
• Incorrect labelling
• Excessive stirring during synthesis

Correct Answer: Hydrolysis due to moisture

Q2. Which analytical technique is preferred for quantifying low‑level volatile residual solvents?

• High‑performance liquid chromatography (HPLC)
• Gas chromatography (GC)
• Inductively coupled plasma mass spectrometry (ICP‑MS)
• Ultraviolet spectrophotometry (UV)

Correct Answer: Gas chromatography (GC)

Q3. Elemental impurities such as lead and cadmium in drug substances are typically assessed by which method?

• Karl Fischer titration
• GC‑MS
• ICP‑MS
• TLC

Correct Answer: ICP‑MS

Q4. A synthetic by‑product formed from incomplete reaction is classified as which type of impurity?

• Process‑related impurity
• Degradation product
• Microbial contaminant
• Packaging leachable

Correct Answer: Process‑related impurity

Q5. Which regulatory guideline provides limits and assessment for residual solvents?

• ICH Q3A
• ICH Q3B
• ICH Q3C
• ICH Q3D

Correct Answer: ICH Q3C

Q6. Photodegradation impurities are most likely produced by exposure to which factor?

• High humidity
• Light (UV/visible)
• Metal catalysts
• Microbial enzymes

Correct Answer: Light (UV/visible)

Q7. Which impurity source is directly related to improper cleaning of equipment and cross‑contamination?

• Residual solvents
• Cross‑contamination with other products
• Oxidation products
• Polymorphic impurity

Correct Answer: Cross‑contamination with other products

Q8. Endotoxins in parenteral products arise from which source?

• Organic solvent residues
• Gram‑negative bacterial contamination
• Heavy metal impurities
• Photolytic degradation

Correct Answer: Gram‑negative bacterial contamination

Q9. Which impurity category is of special concern due to potential genotoxicity even at very low levels?

• Elemental impurities
• Genotoxic impurities (mutagenic)
• Microbial impurities
• Polymorphic forms

Correct Answer: Genotoxic impurities (mutagenic)

Q10. Which test is routinely used to detect residual water content that can cause hydrolytic impurities?

• Karl Fischer titration
• DSC (differential scanning calorimetry)
• ICP‑MS
• TLC

Correct Answer: Karl Fischer titration

Q11. Which of the following is NOT a typical source of impurities in medicinal agents?

• Degradation during storage
• Intentional labeling information
• Residual catalysts from synthesis
• Leachables from packaging

Correct Answer: Intentional labeling information

Q12. Leachables and extractables are impurities originating from which source?

• Active pharmaceutical ingredient (API) synthesis
• Packaging materials and container closure systems
• Analytical reagents
• Environmental air

Correct Answer: Packaging materials and container closure systems

Q13. Which impurity control strategy reduces formation of oxidative impurities?

• Exposing product to sunlight
• Adding appropriate antioxidants and oxygen exclusion
• Increasing storage humidity
• Using acidic catalysts

Correct Answer: Adding appropriate antioxidants and oxygen exclusion

Q14. Which analytical method is most suitable for detecting non‑volatile organic impurities and degradants in a drug substance?

• Gas chromatography (GC)
• High‑performance liquid chromatography (HPLC)
• Flame photometry
• Microbial limit test

Correct Answer: High‑performance liquid chromatography (HPLC)

Q15. Residual metallic catalysts used in synthesis commonly contribute which type of impurity?

• Elemental impurities
• Degradation products
• Microbial endotoxins
• Solvent residues

Correct Answer: Elemental impurities

Q16. Which practice during formulation helps minimize microbial contamination of non‑sterile dosage forms?

• Using non‑validated water sources
• Implementing good manufacturing practices (GMP) and validated sanitization
• Skipping preservative efficacy testing
• Allowing open product exposure

Correct Answer: Implementing good manufacturing practices (GMP) and validated sanitization

Q17. The presence of unexpected peaks in an HPLC impurity profile most likely indicates what?

• Instrument is off
• Unknown impurity or degradant present
• Correct sample purity
• Complete absence of impurities

Correct Answer: Unknown impurity or degradant present

Q18. Which guideline covers assessment of elemental impurities in pharmaceuticals?

• ICH Q3A
• ICH Q3C
• ICH Q3D
• ICH Q2

Correct Answer: ICH Q3D

Q19. Which solvent class contains solvents to be limited or avoided due to toxicity (ICH class 2)?

• Class 1 (to be avoided)
• Class 2 (to be limited)
• Class 3 (low toxic potential)
• Class 4 (not defined)

Correct Answer: Class 2 (to be limited)

Q20. Microbial contamination that produces pyrogens is most likely detected by which assay for parenteral products?

• Microbial limit test
• LAL test (Limulus amebocyte lysate)
• Thin layer chromatography
• Karl Fischer titration

Correct Answer: LAL test (Limulus amebocyte lysate)

Q21. Which processing parameter most directly influences formation of polymorphic impurity?

• Reaction stoichiometry
• Crystallization conditions (temperature, solvent, rate)
• Type of packaging label
• GC column selection

Correct Answer: Crystallization conditions (temperature, solvent, rate)

Q22. Which impurity type can arise from interaction between drug formulation and container closure under accelerated conditions?

• Process‑related impurity
• Leachable impurity
• Residual solvent
• Analytical blank

Correct Answer: Leachable impurity

Q23. What is the best preventive measure against light‑induced impurities in photosensitive APIs?

• Storage in clear glass under fluorescent light
• Packaging in light‑protective (amber/opaque) containers
• Adding water to formulations
• Using metal catalysts

Correct Answer: Packaging in light‑protective (amber/opaque) containers

Q24. Which term describes impurities formed from chemical breakdown of the API during storage?

• Impurity by design
• Degradation products
• Elemental impurities
• Analytical standards

Correct Answer: Degradation products

Q25. Which analytical approach helps identify unknown impurities by providing mass information?

• HPLC with UV detection only
• GC with flame ionization detector
• Mass spectrometry (MS) or LC‑MS
• Visual inspection

Correct Answer: Mass spectrometry (MS) or LC‑MS

Q26. Which of the following is a common source of volatile organic impurities in APIs?

• Residual solvents from recrystallization
• Polymorphic conversion
• Heavy metal catalysts
• Endotoxin contamination

Correct Answer: Residual solvents from recrystallization

Q27. Why are control limits for impurities important in drug development?

• They increase manufacturing cost without benefit
• They ensure safety, efficacy and regulatory compliance
• They are optional suggestions only
• They prevent analytical testing

Correct Answer: They ensure safety, efficacy and regulatory compliance

Q28. Which impurity monitoring is critical during forced degradation studies?

• Establishing degradation pathways and potential toxic degradants
• Only monitor appearance
• Avoid any analytical characterization
• Ignore degradation as irrelevant

Correct Answer: Establishing degradation pathways and potential toxic degradants

Q29. Which of the following is a common metal impurity introduced from stainless steel reactors?

• Sodium chloride
• Iron and nickel
• Organic peroxides
• Residual solvents

Correct Answer: Iron and nickel

Q30. Which control measure helps minimize solvent residues in the final drug substance?

• Insufficient drying time
• Optimized drying, purification and validated solvent removal processes
• Using excessive catalyst amounts
• Deliberately adding solvent at final stage

Correct Answer: Optimized drying, purification and validated solvent removal processes

G S Sachin

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.

Mail- Sachin@pharmacyfreak.com