Spray Drying – Principles & Equipment MCQs With Answer

Introduction: Spray drying is a core unit operation in pharmaceutical production, converting liquid feeds into free-flowing powders through atomization and rapid drying with hot gas. This blog offers focused MCQs on Spray Drying – Principles & Equipment tailored for M.Pharm students studying MIP 203T. Questions delve into atomizer types, drying kinetics, thermal and mechanical stresses on biopharmaceuticals, particle formation, process control parameters (inlet/outlet temperatures, feed properties, residence time), cyclone separation, scale-up challenges and analytical methods for moisture and stability. Each MCQ is designed to test conceptual understanding and practical decision-making required for formulation development, process optimization and quality assurance in spray drying operations.

Q1. What is the basic principle of spray drying in pharmaceutical manufacturing?

• Atomization of the feed into a heated gas stream to evaporate solvent and form dry particles
• Freeze-concentrating a solution and sublimating ice under vacuum
• Compressing powders under high pressure to form dense granules
• Spraying molten material into a cold chamber to solidify droplets

Correct Answer: Atomization of the feed into a heated gas stream to evaporate solvent and form dry particles

Q2. Which atomizer type is most commonly used in pharmaceutical spray dryers for versatile control of droplet size and flow rates?

• Rotary (centrifugal) atomizer
• Two-fluid (pneumatic) nozzle
• Pressure (single-fluid) nozzle
• Ultrasonic atomizer

Correct Answer: Two-fluid (pneumatic) nozzle

Q3. For heat-sensitive biologics, which spray drying gas-flow configuration is generally preferred to minimize thermal exposure?

• Counter-current (feed enters opposite to hot gas)
• Co-current (feed and hot gas enter same direction)
• Mixed flow with recirculated gas
• Static bed drying after atomization

Correct Answer: Co-current (feed and hot gas enter same direction)

Q4. Which factor has the greatest direct impact on primary particle size in spray-dried powders?

• Atomizer type and operating parameters (droplet size distribution)
• Final storage humidity
• Container closure system
• Analytical method used for particle sizing

Correct Answer: Atomizer type and operating parameters (droplet size distribution)

Q5. Why is the glass transition temperature (Tg) critical during spray drying of amorphous pharmaceutical formulations?

• Tg determines the volatility of the solvent
• Tg marks the temperature above which particles become sticky and prone to wall deposition
• Tg controls the color development during drying
• Tg only affects crystalline materials, not amorphous ones

Correct Answer: Tg marks the temperature above which particles become sticky and prone to wall deposition

Q6. What primarily determines gas residence time inside a spray dryer?

• Atomizer nozzle material
• Dryer geometry and gas flow rate
• Choice of solvent in feed
• Particle density of the product

Correct Answer: Dryer geometry and gas flow rate

Q7. In spray drying process monitoring, what does the outlet air temperature most directly indicate?

• Inlet air humidity
• Residual moisture level and end-point of drying in the powder
• Particle size distribution
• Solvent boiling point

Correct Answer: Residual moisture level and end-point of drying in the powder

Q8. Which drying-rate behavior is typically observed during spray drying of droplets into particles?

• Only a constant-rate period until complete drying
• Only a falling-rate period without a constant-rate period
• A constant-rate period followed by one or more falling-rate periods
• No identifiable drying-rate periods due to turbulent flow

Correct Answer: A constant-rate period followed by one or more falling-rate periods

Q9. Which solvent is most commonly used in pharmaceutical spray drying and therefore most critical for process safety and solubility considerations?

• Methanol
• Acetone
• Water
• Ethyl acetate

Correct Answer: Water

Q10. What is the main function of a cyclone separator connected to a spray dryer?

• Condense solvent vapors into liquid form
• Collect and separate dried particles from the exhaust gas by centrifugal force
• Reduce inlet air temperature before atomization
• Provide sterile filtration of incoming air

Correct Answer: Collect and separate dried particles from the exhaust gas by centrifugal force

Q11. Which scale-up parameters are most critical to maintain similar particle properties when moving from lab to production spray dryers?

• Mean droplet diameter (mass median diameter) and spray specific surface area
• Color and odor of the product
• Type of feed container used in lab runs
• Brand of compressor supplying atomization air

Correct Answer: Mean droplet diameter (mass median diameter) and spray specific surface area

Q12. Which analytical technique is most appropriate for accurate quantification of low residual water content in spray-dried pharmaceuticals?

• Loss on drying (gravimetric) alone
• Karl Fischer titration
• UV–Vis spectroscopy
• pH measurement

Correct Answer: Karl Fischer titration

Q13. Increasing inlet air temperature while keeping other parameters constant commonly results in which of the following effects?

• Slower drying rate and increased residual moisture
• Faster drying rate with increased risk of thermal degradation and potential yield loss
• No change to drying kinetics or product quality
• Immediate crystallization of amorphous solutes in all cases

Correct Answer: Faster drying rate with increased risk of thermal degradation and potential yield loss

Q14. In a centrifugal (rotary) atomizer, how does increasing the disk rotational speed affect particle size?

• Increases mean droplet and particle size
• Decreases mean droplet and particle size
• Has no effect on droplet size, only on shape
• Only affects density, not size

Correct Answer: Decreases mean droplet and particle size

Q15. When spray drying therapeutic proteins, which formulation strategy most helps preserve activity during drying?

• Using high inlet temperatures without stabilizers to ensure rapid water removal
• Incorporating stabilizing excipients (e.g., trehalose) and optimizing low thermal exposure
• Minimizing solids content to below 0.1% w/v
• Using only organic solvents to reduce water interactions

Correct Answer: Incorporating stabilizing excipients (e.g., trehalose) and optimizing low thermal exposure

Q16. How do hygroscopic excipients affect the storage behavior of spray-dried powders?

• They reduce moisture uptake and improve flowability
• They increase moisture uptake leading to caking, reduced flow and possible recrystallization
• They make powders completely inert to environmental humidity
• They convert amorphous solids into stable crystalline forms instantly

Correct Answer: They increase moisture uptake leading to caking, reduced flow and possible recrystallization

Q17. Which combination of feed and process variables most strongly influences final particle morphology in spray drying?

• Feed pH and syringe pump brand
• Feed solids concentration and drying kinetics (evaporation rate)
• Ambient lighting and operator skill
• Container color and atomizer nozzle color

Correct Answer: Feed solids concentration and drying kinetics (evaporation rate)

Q18. What is the predominant cause of particle wall deposition (stickiness) inside the drying chamber?

• Particles being too dense and bouncing off walls
• Particle surface temperature remaining above glass transition leading to tackiness
• Excessive centrifugal force from the cyclone
• Use of ultrasonic atomizers only

Correct Answer: Particle surface temperature remaining above glass transition leading to tackiness

Q19. Compared to freeze-drying, spray drying is generally characterized by which of the following?

• Slower processing and higher capital cost
• Continuous operation, faster throughput and lower cost but higher thermal exposure risk
• Better for extremely heat-sensitive materials in all cases
• Always produces more stable amorphous solids than freeze-drying

Correct Answer: Continuous operation, faster throughput and lower cost but higher thermal exposure risk

Q20. For cleaning validation of a spray dryer used for multiple products, which practice is essential to prevent cross-contamination?

• Only visual inspection between product runs
• Use of validated CIP/SIP procedures and analytical verification for product residues in atomizer, cyclone and collection vessels
• Changing the inlet air filter but no internal cleaning
• Relying solely on downstream filtration to remove residues

Correct Answer: Use of validated CIP/SIP procedures and analytical verification for product residues in atomizer, cyclone and collection vessels

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