Principles of Differential Scanning Calorimetry (DSC) MCQs With Answer

Principles of Differential Scanning Calorimetry (DSC) MCQs With Answer — Differential Scanning Calorimetry (DSC) is a core thermal analysis technique in pharmaceutical analysis, allowing measurement of heat flow associated with physical and chemical transitions in drugs and excipients. This introduction covers DSC principles, instrumentation, heat flux vs power-compensated systems, thermogram interpretation, glass transition, melting, crystallization, polymorphism, enthalpy determination and calibration. Emphasis on sample preparation, heating rate effects, baseline correction, modulated DSC and compatibility testing equips B. Pharm students for formulation development, stability studies and quality control. Keywords: DSC, thermal analysis, enthalpy, glass transition, melting point, thermogram, polymorphism. ‘Now let’s test your knowledge with 30 MCQs on this topic.’

Q1. Which quantity does DSC directly measure during a thermal event?

• Mass change of the sample
• Heat flow to or from the sample
• Optical absorbance change
• Electrical conductivity

Correct Answer: Heat flow to or from the sample

Q2. What is the typical sign of an endothermic peak in a DSC heat-flow versus temperature curve (thermogram)?

• Downward peak (negative heat flow)
• Upward peak (positive heat flow)
• No peak; only baseline shift
• Sharp oscillation without peak area

Correct Answer: Upward peak (positive heat flow)

Q3. Which transition is identified as a step change in baseline rather than a sharp peak in DSC?

• Melting point
• Glass transition (Tg)
• Crystallization peak
• Combustion

Correct Answer: Glass transition (Tg)

Q4. Which calibration standard is commonly used to calibrate DSC temperature and enthalpy?

• Silicon
• Indium
• Water
• Carbon

Correct Answer: Indium

Q5. In DSC, what does the onset temperature of a melting peak represent?

• The temperature at which the sample is fully molten
• The temperature where heat flow returns to baseline
• The initial temperature where melting begins
• The peak maximum temperature

Correct Answer: The initial temperature where melting begins

Q6. Which parameter is obtained by integrating the area under a DSC peak?

• Heat capacity (Cp)
• Mass loss
• Enthalpy change (ΔH)
• Thermal conductivity

Correct Answer: Enthalpy change (ΔH)

Q7. How does increasing the heating rate generally affect DSC peak temperatures?

• Shifts peaks to lower temperatures
• Shifts peaks to higher temperatures
• Has no effect on peak position
• Eliminates peaks entirely

Correct Answer: Shifts peaks to higher temperatures

Q8. Which DSC configuration uses two separate furnaces to maintain the sample and reference at equal temperatures?

• Heat flux DSC
• Power-compensated DSC
• Thermogravimetric DSC
• Modulated DSC

Correct Answer: Power-compensated DSC

Q9. What is modulated DSC (MDSC) primarily used to separate?

• Mass loss from heat flow
• Reversible heat capacity changes from irreversible transitions
• Oxidation from reduction reactions
• Sample and pan heat capacities

Correct Answer: Reversible heat capacity changes from irreversible transitions

Q10. Which sample pan material is most commonly used for routine DSC of pharmaceuticals?

• Gold
• Aluminum
• Graphite
• Glass

Correct Answer: Aluminum

Q11. In compatibility studies by DSC, what indicates possible interaction between drug and excipient?

• No change in thermogram compared to pure components
• Appearance of new peaks or disappearance/shift of characteristic peaks
• Lower baseline noise
• Higher sample mass after heating

Correct Answer: Appearance of new peaks or disappearance/shift of characteristic peaks

Q12. Which factor is critical to accurately determine Tg in DSC?

• Sample color
• Appropriate heating/cooling rate and baseline subtraction
• Using an oxidizing purge gas
• Maximum sample mass only

Correct Answer: Appropriate heating/cooling rate and baseline subtraction

Q13. Why are hermetic pans used in DSC measurements?

• To increase thermal conductivity
• To prevent loss of volatile components and control atmosphere
• To make pans reusable
• To alter baseline curvature

Correct Answer: To prevent loss of volatile components and control atmosphere

Q14. Which kinetic analysis method is commonly applied to DSC data for decomposition studies?

• Kissinger method
• HPLC calibration
• UV-Vis spectroscopy
• Karl Fischer titration

Correct Answer: Kissinger method

Q15. What does a negative peak typically indicate in a DSC trace when plotted as heat flow versus temperature (in some instrument conventions)?

• Endothermic event
• Exothermic event
• No thermal event
• Instrument malfunction

Correct Answer: Exothermic event

Q16. Which phenomenon can produce overlapping peaks in a DSC thermogram?

• Simultaneous glass transition and melting of different components
• Perfectly pure single component
• Very low sample mass only
• Using indium calibration

Correct Answer: Simultaneous glass transition and melting of different components

Q17. What is the effect of sample mass on DSC sensitivity and resolution?

• Very large mass always improves resolution
• Too small mass reduces signal; too large mass broadens peaks and reduces resolution
• Mass has no effect on DSC data quality
• Only pan material matters, not mass

Correct Answer: Too small mass reduces signal; too large mass broadens peaks and reduces resolution

Q18. Which purge gas is commonly used in DSC to provide an inert atmosphere?

• Air
• Nitrogen (N2)
• Chlorine
• Oxygen

Correct Answer: Nitrogen (N2)

Q19. How is the heat capacity (Cp) of a sample determined by DSC?

• From onset temperature of melting alone
• From the baseline shift and calibration using standard materials
• By weighing the pan only
• By integrating a crystallization peak

Correct Answer: From the baseline shift and calibration using standard materials

Q20. Which DSC observation suggests polymorphism in an active pharmaceutical ingredient?

• A single sharp melting peak identical to literature
• Multiple melting peaks or melting–recrystallization behavior
• Flat baseline with no transitions
• Only exothermic degradation peaks

Correct Answer: Multiple melting peaks or melting–recrystallization behavior

Q21. What is the primary advantage of heat-flux DSC over power-compensated DSC?

• Faster heating rates only
• Simple sensor design and easier sample comparison due to single furnace
• Requires no calibration
• Eliminates the need for reference pans

Correct Answer: Simple sensor design and easier sample comparison due to single furnace

Q22. Which DSC feature is most useful to detect residual solvents in a pharmaceutical sample?

• Sharp endothermic melting peak only
• Low-temperature endothermic events or mass loss correlated with TG
• Change in sample color during heating
• High baseline noise at all temperatures

Correct Answer: Low-temperature endothermic events or mass loss correlated with TG

Q23. What is the role of baseline subtraction in DSC data processing?

• To increase sample mass
• To remove instrument-related background and reveal true transition signals
• To change peak directions
• To calibrate the balance

Correct Answer: To remove instrument-related background and reveal true transition signals

Q24. Which term describes the temperature at which crystallization begins during cooling?

• Onset temperature of crystallization (Tc onset)
• Glass transition temperature (Tg)
• Boiling point
• Oxidation onset temperature

Correct Answer: Onset temperature of crystallization (Tc onset)

Q25. In formulation development, why is DSC important for selecting excipients?

• It measures color compatibility
• It reveals thermal compatibility, possible interactions and effects on stability
• It determines microbial contamination
• It replaces dissolution testing

Correct Answer: It reveals thermal compatibility, possible interactions and effects on stability

Q26. Which observation indicates oxidative degradation in DSC when testing pharmaceuticals in air?

• Endothermic melting peak only
• Appearance of an exothermic peak at elevated temperatures
• Lower baseline noise
• Immediate mass gain

Correct Answer: Appearance of an exothermic peak at elevated temperatures

Q27. What is the purpose of running an empty reference pan in DSC experiments?

• To add mass to the instrument
• To provide a baseline thermal signal for comparison with the sample pan
• To calibrate the balance only
• To generate additional heat flow

Correct Answer: To provide a baseline thermal signal for comparison with the sample pan

Q28. Which DSC-derived parameter can help estimate the purity of a crystalline drug?

• Peak area of crystallization only
• Melt onset depression and peak shape comparison (Van’t Hoff method)
• Baseline noise level
• Sample color change upon melting

Correct Answer: Melt onset depression and peak shape comparison (Van’t Hoff method)

Q29. How does modulated DSC improve detection of overlapping thermal events?

• By increasing sample mass dramatically
• By applying a sinusoidal temperature modulation to separate reversing and non-reversing signals
• By using a different purge gas
• By removing the reference pan

Correct Answer: By applying a sinusoidal temperature modulation to separate reversing and non-reversing signals

Q30. Which practice improves reproducibility of DSC measurements in a pharmaceutical laboratory?

• Varying heating rates between runs
• Consistent sample mass, pan type, heating rate, and instrument calibration
• Using uncalibrated instruments for speed
• Skipping baseline runs

Correct Answer: Consistent sample mass, pan type, heating rate, and instrument calibration

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