Instrumentation and applications of TGA MCQs With Answer

Thermogravimetric analysis (TGA) is a key thermal technique that measures mass changes of pharmaceutical materials as a function of temperature or time. For B. Pharm students, understanding TGA instrumentation—furnace, microbalance, crucible, thermocouple, purge gas and software—and operational parameters like heating rate, atmosphere, sample mass and calibration is essential. TGA helps assess thermal stability, moisture/volatile loss, decomposition steps, ash/char yield, excipient–drug compatibility and degradation kinetics; coupling with FTIR or MS identifies evolved gases. Mastering TGA interpretation (weight-loss steps, onset and Tmax, DTG peaks, activation energy) supports formulation development, shelf-life prediction and quality control. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What primary signal does a TGA instrument measure?

• Heat flow versus temperature
• Mass change versus temperature or time
• Infrared absorbance of evolved gases
• Pressure change in the sample chamber

Correct Answer: Mass change versus temperature or time

Q2. Which component of a TGA holds the sample directly during analysis?

• Furnace
• Crucible (sample pan)
• Mass flow controller
• Thermocouple junction

Correct Answer: Crucible (sample pan)

Q3. Why is sample mass kept small in TGA experiments?

• To increase baseline noise
• To minimize temperature gradients and improve resolution
• To prevent instrument overheating
• To avoid the need for calibration

Correct Answer: To minimize temperature gradients and improve resolution

Q4. Which gas is commonly used as an inert purge in TGA to prevent oxidation?

• Oxygen
• Nitrogen
• Carbon dioxide
• Hydrogen

Correct Answer: Nitrogen

Q5. What does a DTG (derivative thermogravimetry) curve represent?

• Integral of mass versus time
• Rate of mass loss versus temperature
• Heat flow versus temperature
• Gas composition versus time

Correct Answer: Rate of mass loss versus temperature

Q6. Which parameter strongly affects the position and resolution of decomposition steps in TGA?

• Sample color
• Heating rate
• Instrument serial number
• Operator height

Correct Answer: Heating rate

Q7. What information can coupling TGA with FTIR provide?

• Mass calibration data
• Identification of evolved gas functional groups
• Improved temperature uniformity
• Higher heating rates

Correct Answer: Identification of evolved gas functional groups

Q8. In pharmaceutical analysis, TGA is frequently used to determine:

• Viscosity of liquid formulations
• Moisture/volatile content and thermal stability
• Optical rotation of chiral drugs
• pH of suspensions

Correct Answer: Moisture/volatile content and thermal stability

Q9. What is “onset temperature” in the context of a TGA curve?

• The temperature where the instrument is switched on
• The temperature at which significant mass loss begins
• The maximum furnace temperature
• The temperature where the sample melts

Correct Answer: The temperature at which significant mass loss begins

Q10. Which crucible material is preferred for high-temperature oxidative TGA experiments?

• Aluminum foil
• Platinum
• Glass slide
• Plastic vial

Correct Answer: Platinum

Q11. Which analysis mode keeps temperature constant to observe mass changes over time?

• Dynamic (ramped) mode
• Isothermal mode
• Oscillatory mode
• Derivative mode

Correct Answer: Isothermal mode

Q12. How does an increased heating rate typically influence the apparent decomposition temperature?

• Shifts decomposition to lower temperatures
• Shifts decomposition to higher temperatures
• No change in decomposition temperature
• Makes the curve flatter without shifting

Correct Answer: Shifts decomposition to higher temperatures

Q13. For kinetic analysis of decomposition using TGA, which method estimates activation energy from non-isothermal data?

• Kissinger and Ozawa methods
• HPLC calibration
• Spectrophotometry
• pKa determination

Correct Answer: Kissinger and Ozawa methods

Q14. What does “char yield” refer to in a TGA experiment?

• The mass of evolved gases
• The residual mass remaining after thermal decomposition
• The initial sample mass
• The temperature at which the sample ignites

Correct Answer: The residual mass remaining after thermal decomposition

Q15. Which sample property can cause overlapping mass-loss steps and complicate interpretation?

• High purity
• Complex mixtures of drug and excipients
• Small surface area
• Low molecular weight

Correct Answer: Complex mixtures of drug and excipients

Q16. When doing proximate analysis by TGA for a polymer, typical steps include:

• Moisture loss, volatile release, polymer backbone decomposition, ash formation
• pH adjustment, dilution, filtration, drying
• Optical microscopy, melting point, refractive index, viscosity
• Ion exchange, titration, centrifugation, lyophilization

Correct Answer: Moisture loss, volatile release, polymer backbone decomposition, ash formation

Q17. What role does a thermocouple play in TGA?

• Measures sample mass
• Measures temperature of the furnace or sample
• Pumps purge gas
• Records infrared spectra

Correct Answer: Measures temperature of the furnace or sample

Q18. Which artifact can arise from too large a sample in TGA?

• Improved baseline stability
• Temperature gradient causing broadened peaks and shifted events
• Faster desorption of volatiles
• Automatic correction of mass calibration

Correct Answer: Temperature gradient causing broadened peaks and shifted events

Q19. What is a common reason to run TGA under oxidative atmosphere (air or O2)?

• To prevent any mass loss
• To study combustion and oxidative degradation mechanisms
• To increase instrument sensitivity to moisture
• To clean the balance between runs

Correct Answer: To study combustion and oxidative degradation mechanisms

Q20. Which of the following is a typical application of TGA in drug-excipient compatibility studies?

• Measuring drug dissolution rate in vitro
• Detecting changes in decomposition profile when drug and excipient are mixed
• Determining microbial load of formulations
• Evaluating optical purity of a chiral drug

Correct Answer: Detecting changes in decomposition profile when drug and excipient are mixed

Q21. How does coupling TGA with mass spectrometry (TGA-MS) enhance analysis?

• By increasing furnace temperature range
• By identifying molecular masses of evolved gases
• By directly measuring sample pH
• By reducing sample mass requirement to zero

Correct Answer: By identifying molecular masses of evolved gases

Q22. Baseline drift in TGA can be caused by:

• Perfect instrument calibration
• Changes in buoyancy due to gas flow or temperature and balance instability
• Using too small a crucible
• Running at extremely low heating rates only

Correct Answer: Changes in buoyancy due to gas flow or temperature and balance instability

Q23. Which parameter is MOST important to report when publishing TGA data for reproducibility?

• Sample color
• Heating rate, atmosphere, sample mass and crucible type
• Operator name
• Room humidity only

Correct Answer: Heating rate, atmosphere, sample mass and crucible type

Q24. In TGA, a two-step mass loss for a pharmaceutical solid may indicate:

• Instrument malfunction
• Sequential loss of adsorbed water followed by decomposition of the active compound
• Complete sample stability with no events
• Only melting followed by vaporization

Correct Answer: Sequential loss of adsorbed water followed by decomposition of the active compound

Q25. Why is calibration with reference materials necessary in TGA?

• To increase sample mass
• To verify temperature accuracy and balance performance
• To change chemical composition of the sample
• To alter the heating rate automatically

Correct Answer: To verify temperature accuracy and balance performance

Q26. Which outcome indicates hygroscopic behavior detected by TGA?

• Immediate combustion at room temperature
• Initial mass loss at low temperatures corresponding to water loss
• No mass change up to 800 °C
• Sharp exothermic peak in DTG without mass change

Correct Answer: Initial mass loss at low temperatures corresponding to water loss

Q27. For studying slow decomposition kinetics, which TGA approach is most appropriate?

• High heating rate dynamic scan only
• Isothermal TGA at relevant temperatures for extended time
• Single-point mass measurement at ambient
• DSC without mass analysis

Correct Answer: Isothermal TGA at relevant temperatures for extended time

Q28. Which of the following best describes a limitation of TGA?

• It provides direct chemical identification of evolved gases without coupling
• It cannot differentiate overlapping mass-loss events without additional analysis
• It measures pH changes directly
• It replaces all chromatographic techniques

Correct Answer: It cannot differentiate overlapping mass-loss events without additional analysis

Q29. When comparing two formulations, a shift to lower onset decomposition temperature in one formulation suggests:

• Improved thermal stability
• Reduced thermal stability, possible incompatibility or catalysis of degradation
• No significance to stability
• Higher moisture content always

Correct Answer: Reduced thermal stability, possible incompatibility or catalysis of degradation

Q30. Which practice improves quality of TGA data for pharmaceutical samples?

• Using inconsistent sample masses between replicates
• Running replicate analyses, controlled atmosphere, appropriate crucible and blank correction
• Ignoring instrument maintenance
• Running at the maximum heating rate available without validation

Correct Answer: Running replicate analyses, controlled atmosphere, appropriate crucible and blank correction

Download