Isolation of crude drugs by spectroscopy and chromatography MCQs With Answer

Isolation of crude drugs by spectroscopy and chromatography MCQs With Answer

Isolation of crude drugs using spectroscopy and chromatography is a core topic for B.Pharm students, focusing on separation, purification and structural identification of phytochemicals. This concise overview highlights extraction techniques (maceration, Soxhlet, liquid–liquid partitioning), chromatographic methods (TLC, column chromatography, HPLC, GC) and spectroscopic tools (UV-Vis, IR, NMR, MS, LC-MS) for qualitative and quantitative analysis. Emphasis on stationary/mobile phase selection, retention behavior, derivatization, detector choice, sample preparation, validation and troubleshooting prepares students for lab work and research. Keywords: crude drugs, isolation, chromatography, spectroscopy, phytochemicals, HPLC, TLC, NMR, mass spectrometry, analytical separation. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the primary objective when isolating crude drugs from plant material?

• To change the chemical structure of active compounds
• To separate and purify active constituents for identification and study
• To increase the toxicity of the extract
• To remove all pigments regardless of activity

Correct Answer: To separate and purify active constituents for identification and study

Q2. Which feature best describes Soxhlet extraction?

• Cold maceration without solvent recycling
• Continuous hot extraction with solvent recycling
• Gas-phase extraction at room temperature
• Direct chromatographic separation

Correct Answer: Continuous hot extraction with solvent recycling

Q3. Maceration as an extraction technique is characterized by:

• Use of supercritical CO2 only
• Heating under reflux for prolonged hours
• Soaking plant material in solvent at ambient temperature
• Sublimation of volatile constituents

Correct Answer: Soaking plant material in solvent at ambient temperature

Q4. The partition coefficient (P) in liquid–liquid extraction represents:

• Ratio of solvent densities
• Ratio of solute concentration between two immiscible solvents
• Difference in pH between two phases
• Time required for extraction

Correct Answer: Ratio of solute concentration between two immiscible solvents

Q5. In thin-layer chromatography (TLC) Rf value is defined as:

• Ratio of solvent front to plate length
• Ratio of distance moved by compound to distance moved by solvent front
• Distance from origin to solvent front
• Area under the spot

Correct Answer: Ratio of distance moved by compound to distance moved by solvent front

Q6. Which is the most common stationary phase used in TLC for polar compounds?

• Polystyrene resin
• Silica gel
• Cellulose acetate only
• Aluminized polyethylene

Correct Answer: Silica gel

Q7. The key difference between normal-phase and reverse-phase chromatography is:

• Normal-phase uses nonpolar stationary and polar mobile phase
• Reverse-phase uses polar stationary phase and nonpolar mobile phase
• Normal-phase uses polar stationary phase; reverse-phase uses nonpolar (hydrophobic) stationary phase
• They are identical except for detector type

Correct Answer: Normal-phase uses polar stationary phase; reverse-phase uses nonpolar (hydrophobic) stationary phase

Q8. Which detector is most commonly used in HPLC for routine analysis of plant constituents?

• Flame ionization detector (FID)
• UV-Vis photodiode array (PDA) detector
• Thermal conductivity detector (TCD)
• Electrochemical detector without reference

Correct Answer: UV-Vis photodiode array (PDA) detector

Q9. Gas chromatography (GC) is suitable only for analytes that are:

• Thermally unstable and nonvolatile
• Volatile and thermally stable
• High molecular weight nonvolatile polymers
• Only ionic salts in aqueous solution

Correct Answer: Volatile and thermally stable

Q10. Mass spectrometry primarily provides which information about a compound?

• Exact melting point only
• Ultraviolet absorption maxima
• Molecular weight and fragmentation pattern for structural clues
• Specific rotation in solution

Correct Answer: Molecular weight and fragmentation pattern for structural clues

Q11. Typical 1H NMR chemical shift range for aromatic protons is approximately:

• 0.0–1.5 ppm
• 2.0–3.0 ppm
• 6.0–8.5 ppm
• 10.0–12.0 ppm

Correct Answer: 6.0–8.5 ppm

Q12. In IR spectroscopy the strong carbonyl (C=O) stretching absorption typically appears near:

• 3300 cm-1
• 2100 cm-1
• 1700 cm-1
• 800 cm-1

Correct Answer: 1700 cm-1

Q13. In UV-Vis spectroscopy, a bathochromic shift (red shift) usually indicates:

• Decreased conjugation
• Increased conjugation or electron-donating substitution
• Loss of chromophore
• Only solvent evaporation

Correct Answer: Increased conjugation or electron-donating substitution

Q14. Preparative chromatography differs from analytical chromatography mainly by:

• Purpose: isolation of large quantities versus analytical measurement of small amounts
• Using only paper as stationary phase
• Always using GC instead of HPLC
• Not requiring any solvents

Correct Answer: Purpose: isolation of large quantities versus analytical measurement of small amounts

Q15. In normal-phase chromatography, increasing the polarity of the mobile phase generally:

• Increases retention of analytes on the column
• Has no effect on retention
• Decreases retention, causing faster elution
• Causes irreversible adsorption

Correct Answer: Decreases retention, causing faster elution

Q16. A gradient elution in HPLC is most useful when:

• All analytes have identical polarity
• Analytes span a wide range of polarities and retention times
• The system has no detector
• Only inorganic salts are being analyzed

Correct Answer: Analytes span a wide range of polarities and retention times

Q17. Which factor most directly affects Rf values in TLC?

• Detector sensitivity
• Plate thickness only
• Solvent polarity and stationary phase interactions
• pH of the laboratory air

Correct Answer: Solvent polarity and stationary phase interactions

Q18. To reduce tailing of a basic compound on silica gel, one common approach is to:

• Use a stronger oxidizing mobile phase
• Add a basic modifier (e.g., triethylamine) to the mobile phase or plate
• Lower the column temperature to below 0 °C
• Switch to carbon paste stationary phase

Correct Answer: Add a basic modifier (e.g., triethylamine) to the mobile phase or plate

Q19. For trace-level identification and quantitation of complex plant metabolites, the most sensitive hyphenated technique is:

• TLC with UV lamp
• LC-MS/MS (tandem mass spectrometry)
• Refractive index detector alone
• Paper chromatography with iodine stain

Correct Answer: LC-MS/MS (tandem mass spectrometry)

Q20. Which derivatization reagent is commonly used to make polar plant metabolites amenable to GC analysis by silylation?

• BSTFA (N,O-bis(trimethylsilyl)trifluoroacetamide)
• Sodium borohydride only
• Concentrated sulfuric acid
• Acetic acid without catalyst

Correct Answer: BSTFA (N,O-bis(trimethylsilyl)trifluoroacetamide)

Q21. Decreasing HPLC column particle size generally leads to:

• Lower column efficiency and broader peaks
• Increased backpressure and higher efficiency (more theoretical plates)
• No change in performance
• Complete loss of retention

Correct Answer: Increased backpressure and higher efficiency (more theoretical plates)

Q22. The retention factor (k’) in chromatographic terms is calculated as:

• t0 / tR
• (tR – t0) / t0
• tR × t0
• tR + t0

Correct Answer: (tR – t0) / t0

Q23. A photodiode array (PDA) detector advantage is:

• It detects only a single fixed wavelength
• It records full UV-Vis spectra across each eluting peak
• It is insensitive to organic solvents
• It replaces the need for MS entirely

Correct Answer: It records full UV-Vis spectra across each eluting peak

Q24. On silica gel column chromatography, which type of compound generally elutes first?

• Highly polar compounds that form strong hydrogen bonds with silica
• Very basic ionic salts only
• Nonpolar compounds due to weaker interaction with the polar stationary phase
• Only high molecular weight polymers

Correct Answer: Nonpolar compounds due to weaker interaction with the polar stationary phase

Q25. A limitation of UV detection in chromatographic analysis is:

• All compounds give identical UV absorbance
• Non-chromophoric compounds may not be detected
• It is the most selective detector available
• It requires vacuum conditions

Correct Answer: Non-chromophoric compounds may not be detected

Q26. The typical chemical shift range for aliphatic 1H NMR protons is approximately:

• 0.5–2.5 ppm
• 6.0–8.5 ppm
• 9.0–12.0 ppm
• 200–220 ppm

Correct Answer: 0.5–2.5 ppm

Q27. In mass spectrometry the base peak is defined as:

• The peak at highest m/z value
• The most intense peak in the mass spectrum (100% relative intensity)
• The peak corresponding to the molecular ion only
• The first peak in the chromatogram

Correct Answer: The most intense peak in the mass spectrum (100% relative intensity)

Q28. When isolating alkaloids from plant material, the common initial step is to:

• Make the extract strongly basic to precipitate salts
• Acidify the plant extract to convert alkaloids into water-soluble salts
• Expose the material to UV light to degrade impurities
• Directly inject crude powder into GC

Correct Answer: Acidify the plant extract to convert alkaloids into water-soluble salts

Q29. Which change will generally increase the number of theoretical plates (efficiency) in a column?

• Increase particle size of packing material
• Decrease column length drastically
• Reduce particle size of the column packing
• Operate with very low flow rates only

Correct Answer: Reduce particle size of the column packing

Q30. A principal advantage of LC-MS hyphenated techniques in crude drug analysis is:

• They only separate but cannot identify compounds
• The ability to separate, detect and provide mass-based identification of components with high sensitivity
• They require no sample preparation ever
• They are insensitive to matrix effects

Correct Answer: The ability to separate, detect and provide mass-based identification of components with high sensitivity

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