Tests for volatile oils MCQs With Answer

Tests for volatile oils MCQs With Answer is a focused review for B.Pharm students that covers essential topics in pharmacognosy and quality control of volatile (essential) oils. This resource highlights key tests—Clevenger hydrodistillation, steam distillation, specific gravity, refractive index, optical rotation, GC/GC–MS, TLC, and chemical spot tests—used for identification, purity assessment and detection of adulteration. Emphasis is placed on sample preparation, yield calculation, chromatographic fingerprints, and standardization parameters. It integrates assay strategies, adulteration detection and pharmacopoeial limits while building practical laboratory skills. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the primary principle of the Clevenger apparatus used for volatile oil estimation?

• Solvent extraction using polar solvents to solubilize oils
• Steam distillation followed by continuous condensation and separation of oil from aqueous phase
• Soxhlet extraction with non‑polar solvents at elevated temperature
• Supercritical CO2 extraction under high pressure

Correct Answer: Steam distillation followed by continuous condensation and separation of oil from aqueous phase

Q2. Which expression is most commonly used to report volatile oil yield from plant material?

• % w/w (g oil per 100 g plant)
• % v/w (mL oil per 100 g plant)
• % v/v (mL oil per 100 mL solvent)
• ppm (parts per million of oil in plant)

Correct Answer: % v/w (mL oil per 100 g plant)

Q3. Which physico‑chemical constant is most useful for detecting adulteration of an essential oil?

• Melting point
• Specific gravity (relative density)
• Viscosity at 100°C
• Bulk density of powdered drug

Correct Answer: Specific gravity (relative density)

Q4. Refractive index of a volatile oil primarily provides information about:

• Its boiling point only
• Optical purity alone
• Molecular composition and possible adulteration
• Water content in the oil

Correct Answer: Molecular composition and possible adulteration

Q5. Optical rotation measurement of a volatile oil is used to determine:

• Acidity of the oil
• Chiral composition (enantiomeric excess) and optical activity
• Total unsaturated bonds in the oil
• Presence of inorganic salts

Correct Answer: Chiral composition (enantiomeric excess) and optical activity

Q6. Which chromatographic technique is a standard for qualitative and quantitative analysis of volatile oil components?

• High performance liquid chromatography (HPLC) with C18 column
• Gas chromatography (GC) often coupled with mass spectrometry (GC‑MS)
• Paper chromatography using water as mobile phase
• Size exclusion chromatography

Correct Answer: Gas chromatography (GC) often coupled with mass spectrometry (GC‑MS)

Q7. For TLC screening of terpenoids in volatile oils, a widely used spray reagent is:

• Dragendorff’s reagent
• Vanillin‑sulfuric acid reagent
• Biuret reagent
• ninhydrin reagent

Correct Answer: Vanillin‑sulfuric acid reagent

Q8. Which simple chemical test is commonly used to detect aldehydic constituents in volatile oils?

• Schiff’s test (fuchsia color with Schiff reagent)
• Millon’s test for phenols
• Kjeldahl nitrogen test
• Emulsion test for fatty acids

Correct Answer: Schiff’s test (fuchsia color with Schiff reagent)

Q9. Ferric chloride test when applied to a volatile oil sample is primarily indicative of:

• Presence of phenolic constituents
• Presence of chloride ions
• High molecular weight hydrocarbons
• Protein contamination

Correct Answer: Presence of phenolic constituents

Q10. Which solvent is most suitable for preparing volatile oil samples for GC analysis?

• Distilled water
• n‑Hexane or diethyl ether (non‑polar solvent)
• Methanol with 10% water
• Glycerol

Correct Answer: n‑Hexane or diethyl ether (non‑polar solvent)

Q11. A common cause of reduced volatile oil yield during hydrodistillation is:

• Using very small particle size of plant material
• Excessive drying of plant material leading to loss of volatiles
• Adding inert salts (salting out) to the distillation water
• Distilling at atmospheric pressure

Correct Answer: Excessive drying of plant material leading to loss of volatiles

Q12. Which parameter is NOT typically used in pharmacopoeial standardization of essential oils?

• Specific gravity
• Refractive index
• Optical rotation
• Saponification value

Correct Answer: Saponification value

Q13. GC‑MS identification of volatile oil components relies on:

• Retention times only without spectral data
• Mass spectral fragmentation patterns and retention indices
• UV absorption spectra
• Flame ionization detector peak area alone for structure elucidation

Correct Answer: Mass spectral fragmentation patterns and retention indices

Q14. Which storage condition best preserves volatile oil quality?

• Clear glass bottle exposed to sunlight
• Dark glass bottle, tightly closed, stored in cool place under inert gas if possible
• Open container at room temperature
• Plastic bottle in direct heat

Correct Answer: Dark glass bottle, tightly closed, stored in cool place under inert gas if possible

Q15. When validating a GC method for volatile oil quantification, which parameter assesses repeatability?

• Limit of detection (LOD)
• Precision (intra‑day repeatability)
• Robustness
• Specificity

Correct Answer: Precision (intra‑day repeatability)

Q16. Which of the following best describes the term ‘co‑distillation’ in volatile oil extraction?

• Extraction by organic solvent without heating
• Volatile constituents being carried over with steam and distilled together
• Adsorption onto activated charcoal
• Separation by liquid‑liquid partition only

Correct Answer: Volatile constituents being carried over with steam and distilled together

Q17. In GC quantification by area normalization, the percent of a component is obtained by:

• Dividing component peak area by total area of all detected peaks and multiplying by 100
• Using internal standard concentration only
• Counting number of peaks
• Measuring peak height directly without reference

Correct Answer: Dividing component peak area by total area of all detected peaks and multiplying by 100

Q18. Which laboratory practice reduces loss of volatile components during sample preparation?

• Grinding sample to a very fine powder and heating
• Performing extraction at low temperature and minimizing open handling time
• Exposing sample to direct sunlight
• Using hot concentrated acids during preparation

Correct Answer: Performing extraction at low temperature and minimizing open handling time

Q19. A sudden off‑odour and increase in spot count on TLC of an essential oil likely indicates:

• Improved purity
• Oxidative degradation or contamination
• Bacterial growth only
• Decrease in boiling point

Correct Answer: Oxidative degradation or contamination

Q20. Which test can help detect dilution of an essential oil with lower‑grade fixed oil?

• Refractive index and specific gravity comparison with pharmacopeial values
• Testing for protein content
• Measuring electrical conductivity
• Determining ash value

Correct Answer: Refractive index and specific gravity comparison with pharmacopeial values

Q21. What is the role of an internal standard in GC analysis of volatile oils?

• To change the volatility of analytes
• To correct for injection and instrument variability for accurate quantitation
• To react chemically with sample components
• To serve as mobile phase in GC

Correct Answer: To correct for injection and instrument variability for accurate quantitation

Q22. Which class of compounds in volatile oils typically elutes earliest on a non‑polar GC column?

• High molecular weight sesquiterpenes
• Small, highly volatile monoterpenes
• Polymeric resin components
• Non‑volatile sugars

Correct Answer: Small, highly volatile monoterpenes

Q23. Which test would you use to detect phenylpropanoid ethers (e.g., eugenol) in an essential oil?

• Ninhydrin test
• Ferric chloride and specific TLC visualization / GC profiling
• Biuret test for peptides
• Kjeldahl nitrogen estimation

Correct Answer: Ferric chloride and specific TLC visualization / GC profiling

Q24. The term ‘optical rotation [α]D’ reported for an essential oil refers to:

• The density measured at D temperature
• The angle by which plane‑polarized light is rotated by the sample at the sodium D line
• The refractive index at high temperature
• The boiling point at standard pressure

Correct Answer: The angle by which plane‑polarized light is rotated by the sample at the sodium D line

Q25. Which factor most influences the chemical profile and yield of volatile oils in a plant?

• Ambient room color
• Plant species, part used, harvest time and geographical conditions
• Type of laboratory gloves used
• Shape of the storage bottle cap

Correct Answer: Plant species, part used, harvest time and geographical conditions

Q26. During hydrodistillation, adding salt (NaCl) to the distillation water primarily results in:

• Complete hydrolysis of esters
• “Salting out” effect that can increase oil recovery by decreasing oil solubility in water
• Formation of toxic chlorinated by‑products
• Increase in water boiling point beyond practical limits

Correct Answer: “Salting out” effect that can increase oil recovery by decreasing oil solubility in water

Q27. Which is the best approach to confirm identity of a major GC peak in an essential oil?

• Matching retention time only with no reference
• Comparing retention index and matching mass spectrum with reference library or standard
• Measuring refractive index of the peak
• Estimating peak width visually

Correct Answer: Comparing retention index and matching mass spectrum with reference library or standard

Q28. Which safety consideration is most relevant when working with volatile oils in the lab?

• They are always non‑flammable and safe to heat openly
• Many are flammable and can be irritant; use in fume hood with proper PPE
• They react violently with glassware
• They neutralize all acids and bases

Correct Answer: Many are flammable and can be irritant; use in fume hood with proper PPE

Q29. A validated TLC method for essential oil analysis should demonstrate:

• Only colorful spots regardless of reproducibility
• Specificity, reproducibility, and suitable resolution of components
• That solvent always evaporates instantaneously
• That plate background is never developed

Correct Answer: Specificity, reproducibility, and suitable resolution of components

Q30. Which analytical combination gives both quantitative composition and structural information of volatile oil components?

• TLC followed by refractometry
• GC combined with mass spectrometry (GC‑MS)
• Simple odor comparison by sniffing
• pH measurement of the oil

Correct Answer: GC combined with mass spectrometry (GC‑MS)

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