Gas chromatography (GC) applications in herbal analysis MCQs With Answer

Gas chromatography (GC) applications in herbal analysis are essential for B. Pharm students studying phytochemical profiling, quality control, and standardization of botanicals. GC and GC‑MS enable sensitive qualitative and quantitative analysis of volatile and semi‑volatile compounds, providing retention time‑based fingerprinting, compound identification, and purity assessment. Key topics include sample preparation, extraction methods, derivatization, column selection, detector choices, and method validation for regulatory compliance. Understanding GC data interpretation, matrix effects, and troubleshooting improves herbal authentication, adulteration detection, and batch‑to‑batch consistency. This concise, practical overview links theory to lab practice, equipping students for research and industry roles. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the primary separation principle in gas chromatography (GC)?

• Separation based on solubility in a mobile liquid phase
• Separation by ionic charge differences
• Separation based on volatility and partitioning between carrier gas and stationary phase
• Separation by magnetic susceptibility

Correct Answer: Separation based on volatility and partitioning between carrier gas and stationary phase

Q2. Which detector is most commonly used as a universal detector for organic compounds in GC herbal analysis?

• Electron Capture Detector (ECD)
• Flame Ionization Detector (FID)
• Nitrogen‑Phosphorus Detector (NPD)
• Thermal Conductivity Detector (TCD)

Correct Answer: Flame Ionization Detector (FID)

Q3. What does retention time (tR) represent in GC chromatograms?

• Time taken for carrier gas to travel through the instrument
• Time between injection and detector signal maximum for a peak
• Time required for column conditioning
• Time taken to cool the oven after run

Correct Answer: Time between injection and detector signal maximum for a peak

Q4. What is a major advantage of fused‑silica capillary columns over packed columns in GC?

• Greater sample loading capacity
• Higher resolution and sensitivity with lower sample requirements
• Lower operating temperature range
• Compatibility only with ECD detectors

Correct Answer: Higher resolution and sensitivity with lower sample requirements

Q5. Which sample preparation method is commonly used to collect essential oils from plant material for GC analysis?

• Solid‑phase extraction (SPE)
• Hydrodistillation (steam distillation)
• Soxhlet extraction with hexane
• Protein precipitation

Correct Answer: Hydrodistillation (steam distillation)

Q6. Why is derivatization often performed before GC analysis of certain herbal constituents?

• To decrease analyte volatility and increase boiling point
• To convert analytes into more volatile, thermally stable, and detectable forms
• To remove impurities by precipitation
• To increase sample viscosity for injection

Correct Answer: To convert analytes into more volatile, thermally stable, and detectable forms

Q7. What is the main purpose of using an internal standard in quantitative GC analysis?

• To identify unknown peaks by retention time matching
• To correct for injection and sample preparation variability and improve quantitation
• To increase oven temperature uniformly
• To act as a solvent for sample dissolution

Correct Answer: To correct for injection and sample preparation variability and improve quantitation

Q8. When is splitless injection preferred in GC for herbal samples?

• When analytes are present at high concentration and overload is a concern
• When trace-level analytes require maximum sensitivity
• When inlet temperature must be minimized
• For routine analysis of gases only

Correct Answer: When trace-level analytes require maximum sensitivity

Q9. Which carrier gas is most commonly used in GC and is considered inert for many analyses?

• Nitrogen
• Hydrogen
• Helium
• Oxygen

Correct Answer: Helium

Q10. What additional capability does GC‑MS provide compared with GC‑FID in herbal analysis?

• Higher universal response for all organics
• Direct structural information and molecular weight via mass spectra for compound identification
• Better quantitation for inorganic salts
• Ability to analyze nonvolatile macromolecules without derivatization

Correct Answer: Direct structural information and molecular weight via mass spectra for compound identification

Q11. Which detector is selective for nitrogen‑ and phosphorus‑containing compounds often used in pesticide residue analysis of herbs?

• Flame Ionization Detector (FID)
• Nitrogen‑Phosphorus Detector (NPD)
• Electron Capture Detector (ECD)
• Thermal Conductivity Detector (TCD)

Correct Answer: Nitrogen‑Phosphorus Detector (NPD)

Q12. How should the polarity of the GC stationary phase be chosen for separating herbal analytes?

• Always use nonpolar phases regardless of analyte chemistry
• Match stationary phase polarity to analyte polarity to improve selectivity and resolution
• Use polar phases only for volatile oils
• Polarity choice is irrelevant if the oven program is fast

Correct Answer: Match stationary phase polarity to analyte polarity to improve selectivity and resolution

Q13. In method validation, which parameter defines the lowest concentration that can be reliably quantified with acceptable accuracy and precision?

• Limit of Detection (LOD)
• Limit of Quantification (LOQ)
• Linearity range
• System suitability

Correct Answer: Limit of Quantification (LOQ)

Q14. How does increasing the split ratio in split injection affect the chromatographic analysis?

• Increases the amount of sample entering the column, improving sensitivity
• Decreases the fraction of sample entering the column, reducing sensitivity and preventing overload
• Has no effect on sensitivity
• Always increases chromatographic resolution

Correct Answer: Decreases the fraction of sample entering the column, reducing sensitivity and preventing overload

Q15. What is the purpose of the Kovats retention index in GC herb analysis?

• To calibrate detector response factors
• To provide a reproducible retention index for comparing compound retention across different columns and conditions
• To measure column bleed quantitatively
• To set inlet temperature automatically

Correct Answer: To provide a reproducible retention index for comparing compound retention across different columns and conditions

Q16. What common artifact can appear when analyzing thermally labile herbal constituents by GC without proper precautions?

• Formation of solvent clusters only
• Thermal degradation or pyrolysis products creating additional peaks
• Loss of baseline entirely
• Complete invisibility of all peaks

Correct Answer: Thermal degradation or pyrolysis products creating additional peaks

Q17. For analysis of fatty acids from herbal lipids by GC, what derivatization is commonly used prior to injection?

• Formation of fatty acid methyl esters (FAMEs)
• Conversion to amino derivatives
• Oxidation to ketones
• Precipitation with ammonium sulfate

Correct Answer: Formation of fatty acid methyl esters (FAMEs)

Q18. What is headspace GC particularly useful for in herbal analysis?

• Analyzing nonvolatile alkaloids without derivatization
• Analyzing volatile aroma and fragrance compounds in herbs without solvent extraction
• Quantifying heavy metals in plant material
• Measuring intact proteins

Correct Answer: Analyzing volatile aroma and fragrance compounds in herbs without solvent extraction

Q19. Which chromatographic parameter is commonly used to describe column efficiency?

• Retention time (tR)
• Number of theoretical plates (N)
• Injector temperature
• Carrier gas pressure

Correct Answer: Number of theoretical plates (N)

Q20. Which modification to the temperature program is most likely to improve resolution between two closely eluting herbal peaks?

• Increase initial oven temperature substantially
• Use a faster temperature ramp to shorten runtime
• Slow the temperature ramp (decrease ramp rate) in the region of elution
• Turn off temperature programming and keep at a very high isothermal temperature

Correct Answer: Slow the temperature ramp (decrease ramp rate) in the region of elution

Q21. Why is GC fingerprinting useful for herbal quality control?

• It identifies the exact molecular structure of every compound without MS
• It provides reproducible chromatographic profiles for authentication, batch comparison, and detection of adulteration
• It eliminates the need for sample preparation entirely
• It only measures inorganic contaminants

Correct Answer: It provides reproducible chromatographic profiles for authentication, batch comparison, and detection of adulteration

Q22. Which detector provides spectral patterns (m/z values) for fragment ions in GC analysis?

• Flame Ionization Detector (FID)
• Thermal Conductivity Detector (TCD)
• Mass Spectrometer (MS)
• Electron Capture Detector (ECD)

Correct Answer: Mass Spectrometer (MS)

Q23. Which sample introduction technique is solvent‑free and especially useful for trace volatile analysis of herbs?

• Liquid injection of concentrated extract
• Solid‑phase microextraction (SPME)
• Soxhlet extraction
• Direct infusion

Correct Answer: Solid‑phase microextraction (SPME)

Q24. Why is retention time reproducibility important in GC herbal analysis?

• Because it directly controls detector sensitivity
• Because reproducible retention times assist in reliable compound identification and fingerprint comparison
• Because it sets the sample injection volume
• Because it replaces the need for calibration curves

Correct Answer: Because reproducible retention times assist in reliable compound identification and fingerprint comparison

Q25. What is a common cause of peak tailing in GC chromatograms of herbal extracts?

• Overly inert column surface
• Active sites in the column or inlet causing adsorption of analytes
• Too low injection temperature only
• Using helium as carrier gas

Correct Answer: Active sites in the column or inlet causing adsorption of analytes

Q26. What is the role of relative response factors (RRF) in GC quantitation of herbal constituents?

• They standardize oven temperature across instruments
• They correct for differing detector responses between analytes and an internal standard
• They determine the carrier gas flow rate
• They measure column bleed

Correct Answer: They correct for differing detector responses between analytes and an internal standard

Q27. Which calibration approach is best to compensate for matrix effects in complex herbal extracts?

• External calibration with solvent standards only
• Standard addition method
• Using a single-point calibration at a high concentration
• No calibration is required for GC

Correct Answer: Standard addition method

Q28. Why are mass spectral libraries important when using GC‑MS for herbal analysis?

• They provide definitive proof of compound purity without retention data
• They allow tentative identification of compounds by matching measured spectra to reference spectra
• They improve detector linearity
• They are only used for quantitation, not identification

Correct Answer: They allow tentative identification of compounds by matching measured spectra to reference spectra

Q29. Which practice will most effectively improve the limit of detection (LOD) for trace volatiles in GC analysis?

• Use split injection with a high split ratio
• Use splitless injection, concentrate the sample, and employ a selective/sensitive detector
• Decrease detector voltage to reduce noise
• Use a shorter column to speed analysis

Correct Answer: Use splitless injection, concentrate the sample, and employ a selective/sensitive detector

Q30. Which chromatographic parameter quantitatively describes the separation between two adjacent peaks?

• Theoretical plate height (H)
• Retention index (RI)
• Resolution (Rs)
• Carrier gas purity

Correct Answer: Resolution (Rs)

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com