Types of impurities MCQs With Answer

Introduction: Types of Impurities MCQs With Answer for B. Pharm

Types of impurities in pharmaceuticals include organic impurities (process-related impurities, intermediates, degradation products), inorganic impurities (reagents, catalysts, residual salts, elemental impurities), and residual solvents. B. Pharm students must know ICH guidelines (Q3A/Q3B for impurities in drug substances/products, Q3C for residual solvents, Q3D for elemental impurities), pharmacopeial standards (USP, IP, BP), and quality control tools like impurity profiling, limit tests, HPLC/GC/TLC, LC–MS, ICP–MS, and Karl Fischer. Understanding sources (raw materials, synthesis, packaging leachables, microbiological contamination), stability/forced degradation, specifications, thresholds, and risk assessment is vital for GMP-compliant manufacturing and safe medicines. This Student-friendly set provides exam-focused practice on classification, identification, control, and analysis. Now let’s test your knowledge with 50 MCQs on this topic.

Q1. Which statement best defines an impurity in a pharmaceutical substance?

• Any component present in the drug substance that is not the desired active molecule
• Any excipient intentionally added to the formulation
• Only toxic substances introduced during manufacturing
• Only degradation products formed during storage

Correct Answer: Any component present in the drug substance that is not the desired active molecule

Q2. The three primary categories of impurities as per pharmacopeial/ICH classification are:

• Organic impurities, inorganic impurities, residual solvents
• Physical, chemical, biological
• Known, unknown, suspected
• Toxic, non-toxic, inert

Correct Answer: Organic impurities, inorganic impurities, residual solvents

Q3. Process-related impurities are best described as:

• By-products, unreacted starting materials, reagents, and catalysts from synthesis
• Products formed due to long-term storage at high humidity
• Contaminants entering from packaging during distribution
• Microbial endotoxins arising in sterile manufacturing

Correct Answer: By-products, unreacted starting materials, reagents, and catalysts from synthesis

Q4. Degradation products are primarily generated due to:

• Chemical change of the API under stress or storage conditions
• Accidental mixing of raw materials
• Residual solvents not removed during drying
• Inadequate filtration of particulates

Correct Answer: Chemical change of the API under stress or storage conditions

Q5. Which ICH guideline addresses impurities in new drug substances (organic impurities)?

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

Correct Answer: ICH Q3A

Q6. Residual solvents are controlled according to which guideline?

• ICH Q3C
• ICH Q1A
• ICH Q2
• ICH Q10

Correct Answer: ICH Q3C

Q7. Elemental impurities (such as Pd, Pb, Cd) are addressed by:

• ICH Q3D
• ICH Q6A
• ICH Q1B
• ICH E6

Correct Answer: ICH Q3D

Q8. Class 1 residual solvents (ICH Q3C) are characterized as:

• Solvents to be avoided due to unacceptable toxicity
• Solvents with low toxic potential
• Solvents with limited toxic potential
• Solvents used only in parenteral formulations

Correct Answer: Solvents to be avoided due to unacceptable toxicity

Q9. Which is a Class 1 residual solvent?

• Benzene
• Ethanol
• Acetone
• Ethyl acetate

Correct Answer: Benzene

Q10. The most appropriate technique to quantify residual solvents in APIs is:

• Gas chromatography (often with headspace)
• UV–Visible spectrophotometry
• Thin-layer chromatography
• Potentiometric titration

Correct Answer: Gas chromatography (often with headspace)

Q11. The USP general chapter for Residual Solvents testing is:

• USP <467>
• USP <85>
• USP <61>
• USP <701>

Correct Answer: USP <467>

Q12. The outdated “Heavy Metals” colorimetric test (USP <231>) has been replaced by risk-based limits in:

• USP <232> and <233>
• USP <905> and <711>
• USP <85> and <151>
• USP <1231> and <1225>

Correct Answer: USP <232> and <233>

Q13. The preferred instrumental technique to quantify elemental impurities at trace levels is:

• ICP–MS
• HPLC–UV
• Flame photometry
• FT-IR

Correct Answer: ICP–MS

Q14. A simple and accurate method for water content in many drug substances is:

• Karl Fischer titration
• Loss on drying at 105°C
• Gas chromatography
• UV absorbance at 254 nm

Correct Answer: Karl Fischer titration

Q15. “Sulphated ash” primarily estimates:

• Inorganic residue remaining after incineration with sulfuric acid
• Organic volatile impurities
• Moisture content in the sample
• Loss of solvents from the matrix

Correct Answer: Inorganic residue remaining after incineration with sulfuric acid

Q16. Which statement best describes a stability-indicating method?

• An analytical method that separates and quantifies API and all degradation products
• A method validated only for precision
• A method used exclusively for dissolution testing
• A method that measures only API potency

Correct Answer: An analytical method that separates and quantifies API and all degradation products

Q17. Forced degradation studies are performed to:

• Elucidate degradation pathways and develop stability-indicating methods
• Increase API shelf-life artificially
• Reduce the number of impurities formed
• Meet packaging qualification requirements only

Correct Answer: Elucidate degradation pathways and develop stability-indicating methods

Q18. Which is commonly used for oxidative stress in forced degradation?

• Hydrogen peroxide
• Sodium chloride
• Carbon dioxide
• Ethanol

Correct Answer: Hydrogen peroxide

Q19. Which photostability guideline describes light stress testing?

• ICH Q1B
• ICH Q3B
• ICH Q8
• ICH Q9

Correct Answer: ICH Q1B

Q20. In HPLC method validation (ICH Q2), “specificity” refers to the ability to:

• Measure accurately the analyte in presence of impurities and excipients
• Reproduce results across analysts
• Produce linear response with concentration
• Detect small changes in analyte concentration

Correct Answer: Measure accurately the analyte in presence of impurities and excipients

Q21. For initial impurity screening in API synthesis, a rapid and economical technique is:

• Thin-layer chromatography
• Nuclear magnetic resonance
• Differential scanning calorimetry
• Polarimetry

Correct Answer: Thin-layer chromatography

Q22. For structural elucidation of unknown impurities separated by HPLC, the best detector/technique is:

• LC–MS
• Refractive index detector
• Conductivity detector
• Flame ionization detector

Correct Answer: LC–MS

Q23. Headspace sampling in GC is particularly useful for detecting:

• Volatile residual solvents
• Non-volatile inorganic salts
• High-molecular-weight polymers
• Protein impurities

Correct Answer: Volatile residual solvents

Q24. Leachables in pharmaceuticals originate from:

• Packaging materials during storage
• Residual water in the API
• Excipients intentionally added
• Analyst handling during testing

Correct Answer: Packaging materials during storage

Q25. Extractables are defined as:

• Compounds that can be pulled from packaging under aggressive conditions
• Compounds that always migrate into the drug product during storage
• Compounds added as antioxidants to the formulation
• Microbial metabolites produced in culture

Correct Answer: Compounds that can be pulled from packaging under aggressive conditions

Q26. Which is a common source of inorganic impurities?

• Residual catalysts like palladium from hydrogenation
• Photolysis of the API
• Microbial contamination
• Evaporation of ethanol

Correct Answer: Residual catalysts like palladium from hydrogenation

Q27. A typical example of a process solvent that may remain as a residual impurity is:

• Dimethylformamide (DMF)
• Sodium chloride
• Magnesium stearate
• Microcrystalline cellulose

Correct Answer: Dimethylformamide (DMF)

Q28. Microbiological impurities in non-sterile products are controlled by:

• Total aerobic microbial count (TAMC) and total yeast and mold count (TYMC)
• Optical rotation
• Friability test
• Viscosity measurement

Correct Answer: Total aerobic microbial count (TAMC) and total yeast and mold count (TYMC)

Q29. Bacterial endotoxins in parenterals are measured using:

• LAL assay
• HPLC–UV
• GC–FID
• DSC

Correct Answer: LAL assay

Q30. Nitrosamine impurities are of concern primarily because they are:

• Genotoxic and potentially carcinogenic
• Highly volatile but nontoxic
• Inorganic salts that affect taste
• Inert excipients

Correct Answer: Genotoxic and potentially carcinogenic

Q31. A commonly applied concept for acceptable daily intake of most genotoxic impurities is the TTC, approximately:

• 1.5 µg/day
• 15 µg/day
• 0.15 µg/day
• 150 µg/day

Correct Answer: 1.5 µg/day

Q32. In a product specification, impurity limits are expressed as:

• Acceptance criteria for individual and total impurities
• Batch manufacturing records
• Cleaning validation limits
• Supplier qualification requirements

Correct Answer: Acceptance criteria for individual and total impurities

Q33. The “reporting threshold” for impurities means the level at which:

• An impurity must be reported in the documentation
• An impurity must be removed completely
• A toxicology study becomes mandatory
• Regulatory approval is automatically withdrawn

Correct Answer: An impurity must be reported in the documentation

Q34. The “identification threshold” indicates the level at which:

• The structure of the impurity should be identified where feasible
• The impurity may be ignored
• No analytical method is required
• Only visual inspection is needed

Correct Answer: The structure of the impurity should be identified where feasible

Q35. The “qualification threshold” refers to the level at which:

• Safety data may be required to establish acceptability
• Analytical method validation is unnecessary
• Batch must be rejected automatically
• Only organoleptic testing is performed

Correct Answer: Safety data may be required to establish acceptability

Q36. Peak purity assessment in HPLC helps to:

• Ensure a chromatographic peak is not composed of co-eluting impurities
• Measure the melting point of the analyte
• Determine the partition coefficient
• Quantify elemental impurities

Correct Answer: Ensure a chromatographic peak is not composed of co-eluting impurities

Q37. To resolve co-elution of an impurity with API in HPLC, the first strategy is to:

• Modify mobile phase composition or column selectivity
• Increase injection volume
• Raise column temperature indefinitely
• Switch to UV–Vis spectroscopy

Correct Answer: Modify mobile phase composition or column selectivity

Q38. Chiral impurities (undesired enantiomer) are best analyzed using:

• Chiral HPLC columns
• Flame photometry
• Potentiometric titration
• Thin-layer chromatography with silica gel GF

Correct Answer: Chiral HPLC columns

Q39. Which of the following is a Class 3 residual solvent (low toxic potential)?

• Ethanol
• Benzene
• 1,2-Dichloroethane
• Carbon tetrachloride

Correct Answer: Ethanol

Q40. Which factor most increases hydrolytic degradation impurities?

• High moisture content and unsuitable pH
• Low temperature storage
• Amber light-protective packaging
• Use of dry nitrogen headspace

Correct Answer: High moisture content and unsuitable pH

Q41. Limit tests for anions like chloride and sulfate in IP/USP are generally based on:

• Precipitation and turbidity comparison
• Fluorescence intensity
• Potentiometric titration only
• Conductivity exclusively

Correct Answer: Precipitation and turbidity comparison

Q42. The classical limit test for iron in pharmacopeias uses formation of:

• A colored complex compared against a standard
• A volatile ester
• A crystalline polymorph
• An electrochemical deposit

Correct Answer: A colored complex compared against a standard

Q43. The historical Gutzeit method is associated with testing of:

• Arsenic
• Chloride
• Peroxide
• Lead

Correct Answer: Arsenic

Q44. A formulation risk to impurity formation from packaging is best mitigated by:

• Extractables and leachables studies with suitable packaging selection
• Increasing fill volume in the same container
• Adding more colorants
• Using higher compression force in tablets

Correct Answer: Extractables and leachables studies with suitable packaging selection

Q45. ICH Q6A primarily addresses:

• Specifications: test procedures and acceptance criteria
• Photostability testing
• Residual solvents limits
• Validation of analytical procedures

Correct Answer: Specifications: test procedures and acceptance criteria

Q46. A robust control strategy for impurities includes all EXCEPT:

• Ignoring unknown impurities below any level
• Setting specification limits
• Using stability-indicating methods
• Supplier and raw material controls

Correct Answer: Ignoring unknown impurities below any level

Q47. In HPLC impurity profiling, a gradient elution is often preferred because it:

• Improves separation of components with wide polarity range
• Always shortens run time regardless of method
• Eliminates need for column conditioning
• Removes the requirement for system suitability

Correct Answer: Improves separation of components with wide polarity range

Q48. Which change most likely reduces oxidative impurities in a formulation?

• Use of antioxidants and oxygen-impermeable packaging
• Increasing tablet hardness only
• Adding flavors and colors
• Raising storage temperature

Correct Answer: Use of antioxidants and oxygen-impermeable packaging

Q49. The peroxide value test in oils indicates:

• Extent of oxidative rancidity (peroxide impurities)
• Amount of saturated fatty acids
• Level of residual solvents
• Presence of heavy metals

Correct Answer: Extent of oxidative rancidity (peroxide impurities)

Q50. Good Manufacturing Practices (GMP) help control impurities primarily by:

• Preventing contamination and ensuring consistent, validated processes
• Eliminating the need for quality control testing
• Allowing flexible undocumented process changes
• Focusing only on finished product testing

Correct Answer: Preventing contamination and ensuring consistent, validated processes