Principles of Thermal Gravimetric Analysis (TGA) MCQs With Answer

Principles of Thermal Gravimetric Analysis (TGA) MCQs With Answer — Thermal Gravimetric Analysis (TGA) is a core thermal technique in pharmaceutical analysis that measures mass change of a sample as a function of temperature or time under controlled atmosphere. This introduction covers the principles of TGA—mass loss, decomposition, evaporation, and residual ash—instrument components (balance, furnace, crucible), data interpretation (thermogram, onset and peak temperatures, DTG), experimental variables (heating rate, atmosphere, sample mass), and common pharmaceutical applications such as stability testing, moisture and volatile content determination, excipient compatibility, and polymorph screening. These MCQs with answers focus on practical understanding, instrumentation artifacts, and kinetic interpretations relevant to B.Pharm students. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What does Thermal Gravimetric Analysis (TGA) primarily measure?

• The change in mass of a sample as a function of temperature or time
• The heat flow into or out of a sample
• The optical absorbance changes during heating
• The change in electrical conductivity with temperature

Correct Answer: The change in mass of a sample as a function of temperature or time

Q2. Which instrument component directly detects mass change in TGA?

• Furnace
• Thermocouple
• Microbalance or balance sensor
• Gas flow controller

Correct Answer: Microbalance or balance sensor

Q3. What does a thermogram in TGA plot?

• Mass change versus time or temperature
• Heat flow versus temperature
• Infrared spectra versus temperature
• Differential pressure versus time

Correct Answer: Mass change versus time or temperature

Q4. What is DTG in the context of TGA?

• Derivative of mass loss curve (rate of mass change)
• Digital temperature gauge
• Dual thermogravimetric analysis
• Decomposition threshold gradient

Correct Answer: Derivative of mass loss curve (rate of mass change)

Q5. Which atmosphere is commonly used to study oxidative degradation in TGA?

• Nitrogen
• Argon
• Oxygen or air
• Helium

Correct Answer: Oxygen or air

Q6. Why is sample mass kept small in TGA experiments?

• To reduce thermal gradients and ensure uniform heating
• To increase reaction rates of decomposition
• To enhance gas diffusion out of the instrument
• To raise the baseline noise deliberately

Correct Answer: To reduce thermal gradients and ensure uniform heating

Q7. Which experimental variable typically shifts the onset temperature of mass loss to higher values when decreased?

• Increasing sample mass
• Decreasing heating rate
• Switching from inert to oxidizing atmosphere
• Using a reactive crucible material

Correct Answer: Decreasing heating rate

Q8. In pharmaceutical TGA, an initial small mass loss below 150 °C often corresponds to:

• Polymer crosslinking
• Moisture or volatile solvent loss
• Complete thermal decomposition
• Ash formation

Correct Answer: Moisture or volatile solvent loss

Q9. Which crucible material is most suitable for routine TGA under inert conditions for many pharmaceuticals?

• Platinum
• Aluminum foil
• Open glass vial
• Nickel alloy that reacts with sample

Correct Answer: Platinum

Q10. What artifact can occur if sample reacts with the crucible during TGA?

• Baseline drift and erroneous mass loss/gain
• Improved resolution of decomposition steps
• Reduced need for calibration
• Automatic compensation by DTG

Correct Answer: Baseline drift and erroneous mass loss/gain

Q11. In a TGA curve, a plateau after mass loss indicates:

• Continuous evaporation
• Completion of that decomposition or mass-loss step
• Instrument failure
• Ongoing mass gain due to oxidation

Correct Answer: Completion of that decomposition or mass-loss step

Q12. Which coupling technique identifies evolved gases during TGA?

• TGA-DSC
• TGA-FTIR or TGA-MS
• HPLC coupling
• UV-Vis spectroscopy

Correct Answer: TGA-FTIR or TGA-MS

Q13. Which kinetic method is commonly used to estimate activation energy from TGA data without assuming reaction order?

• Coats-Redfern method
• Ozawa-Flynn-Wall (OFW) method
• Henderson-Hasselbalch approach
• Arrhenius plot with fixed conversion

Correct Answer: Ozawa-Flynn-Wall (OFW) method

Q14. What is the effect of increasing heating rate on TGA peaks?

• Peaks shift to lower temperatures and sharpen
• Peaks shift to higher temperatures and may broaden
• No change in peak position
• Baselines become perfectly flat

Correct Answer: Peaks shift to higher temperatures and may broaden

Q15. In TGA, the onset temperature is defined as:

• The temperature at which the instrument reaches maximum heating power
• The temperature where a significant and reproducible deviation from baseline mass begins
• The temperature of maximum DTG peak
• The final temperature of the experiment

Correct Answer: The temperature where a significant and reproducible deviation from baseline mass begins

Q16. How does an oxidative atmosphere affect decomposition compared to inert atmosphere?

• Oxidative atmosphere generally suppresses decomposition
• Oxidative atmosphere can accelerate oxidation and change decomposition pathways
• There is no effect of atmosphere composition
• Inert atmosphere causes combustion

Correct Answer: Oxidative atmosphere can accelerate oxidation and change decomposition pathways

Q17. Which parameter from TGA is most useful to quantify non-volatile residue or ash content?

• Initial mass
• Residual mass at final temperature
• DTG peak height
• Onset temperature

Correct Answer: Residual mass at final temperature

Q18. Which sample property can cause apparent mass gain in TGA?

• Moisture loss
• Oxidation resulting in uptake of oxygen
• Volatilization of plasticizer
• Instrument baseline subtraction

Correct Answer: Oxidation resulting in uptake of oxygen

Q19. For accurate quantitative TGA, calibration of the balance is important because:

• It adjusts the furnace temperature profile
• It ensures measured mass changes are accurate and traceable
• It eliminates the need for reference materials
• It increases the sample decomposition rate

Correct Answer: It ensures measured mass changes are accurate and traceable

Q20. Which of the following is a common use of TGA in formulation development?

• Determining drug solubility in water
• Assessing moisture content and excipient thermal stability
• Measuring tablet hardness
• Determining pH of excipients

Correct Answer: Assessing moisture content and excipient thermal stability

Q21. What does a multi-step mass loss on a TGA curve typically indicate?

• Single-component pure compound only
• Multiple processes such as solvent loss, decomposition, and char formation
• Instrument failure and noise
• Only moisture loss in all steps

Correct Answer: Multiple processes such as solvent loss, decomposition, and char formation

Q22. Which factor can produce thermal lag and affect TGA accuracy at high heating rates?

• Large sample mass or poor thermal contact
• Use of platinum crucibles
• Using an inert purge gas
• Low baseline noise

Correct Answer: Large sample mass or poor thermal contact

Q23. How is isothermal TGA different from dynamic TGA?

• Isothermal TGA holds temperature constant while monitoring mass versus time
• Isothermal TGA ramps temperature continuously
• Isothermal TGA measures heat flow instead of mass
• There is no difference

Correct Answer: Isothermal TGA holds temperature constant while monitoring mass versus time

Q24. Which baseline correction step is important when interpreting small mass changes in TGA?

• Ignoring buoyancy effects
• Subtracting blank run or reference to correct buoyancy and instrument drift
• Running only very large samples
• Removing the furnace shield

Correct Answer: Subtracting blank run or reference to correct buoyancy and instrument drift

Q25. Which TGA result helps distinguish evaporation from chemical decomposition?

• Mass loss coinciding with an endotherm in DSC or loss of volatiles in TGA-FTIR
• Only observing DTG peak without other techniques
• High residual mass only
• Constant baseline throughout

Correct Answer: Mass loss coinciding with an endotherm in DSC or loss of volatiles in TGA-FTIR

Q26. What is the typical consequence of using too large a sample pan in TGA?

• Improved signal-to-noise ratio without effects
• Increased thermal gradients and broadened decomposition peaks
• Automatic baseline stabilization
• Reduced sensitivity to mass change

Correct Answer: Increased thermal gradients and broadened decomposition peaks

Q27. In kinetic analysis of TGA data, the Arrhenius equation links rate constant to:

• Sample color change
• Temperature and activation energy
• Heat capacity only
• Atmosphere flow rate only

Correct Answer: Temperature and activation energy

Q28. Which precaution helps avoid buoyancy artifacts in TGA measurements?

• Using very high heating rates only
• Using matching reference crucible and performing baseline runs with the same gas flow
• Placing sample directly on furnace element
• Not purging the system with gas

Correct Answer: Using matching reference crucible and performing baseline runs with the same gas flow

Q29. Which is an advantage of coupling TGA with MS (mass spectrometry)?

• It measures heat flow more accurately than DSC
• It identifies and quantifies evolved gaseous species by mass-to-charge ratio
• It increases sample decomposition temperature
• It eliminates need for temperature calibration

Correct Answer: It identifies and quantifies evolved gaseous species by mass-to-charge ratio

Q30. When interpreting TGA for polymorph screening, what is a key indicator of different solid forms?

• Identical TGA curves for all forms
• Differences in mass-loss temperatures, onset, and possibly residues indicating distinct thermal behavior
• Only color change on heating
• Mass gains only at low temperatures

Correct Answer: Differences in mass-loss temperatures, onset, and possibly residues indicating distinct thermal behavior

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