Modern extraction methods are indispensable in pharmaceutical analysis, offering efficient isolation of active ingredients from complex matrices. B.Pharm students should master techniques such as solvent extraction, Soxhlet, supercritical fluid extraction (SFE), microwave-assisted extraction (MAE), ultrasonic-assisted extraction (UAE), pressurized liquid extraction (PLE/ASE), and green extraction strategies. Key concepts include solvent polarity, partition coefficient, extraction kinetics and thermodynamics, process optimization, scale-up challenges, co-solvents/modifiers, and analytical coupling with HPLC/GC. Understanding operational parameters, selectivity, yield, purity, safety and regulatory aspects prepares students for research and industry applications. This introduction focuses on practical parameters and troubleshooting for laboratory and industrial extraction. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What does the partition coefficient (K) represent in liquid-liquid extraction?
- The ratio of solute concentration in two immiscible phases at equilibrium
- The ratio of solvent volumes required for extraction
- The temperature at which solvents separate
- The rate constant of mass transfer
Correct Answer: The ratio of solute concentration in two immiscible phases at equilibrium
Q2. Which property of supercritical CO2 makes it attractive for extracting nonpolar, thermolabile compounds?
- High polarity similar to water
- Tunable solvating power with pressure and temperature
- Strong ionic strength
- Permanent chemical reactivity with analytes
Correct Answer: Tunable solvating power with pressure and temperature
Q3. The primary mechanism by which microwave-assisted extraction (MAE) accelerates extraction is:
- Cavitation causing micro-jet formation
- Dielectric heating of solvents and sample matrices
- Formation of supercritical phases
- Selective chemical derivatization of analytes
Correct Answer: Dielectric heating of solvents and sample matrices
Q4. Ultrasonic-assisted extraction (UAE) enhances mass transfer mainly through:
- Generation of high-pressure steam
- Formation and collapse of cavitation bubbles
- Strong magnetic field alignment of molecules
- Permanent solvent phase change
Correct Answer: Formation and collapse of cavitation bubbles
Q5. Which advantage best describes Soxhlet extraction for exhaustive extraction of solid samples?
- It uses supercritical fluids at low pressure
- Continuous hot solvent percolation and recycling for exhaustive extraction
- It always avoids thermal degradation of analytes
- It provides instantaneous extraction in seconds
Correct Answer: Continuous hot solvent percolation and recycling for exhaustive extraction
Q6. For extracting polar glycosides from plant material, which solvent is most suitable?
- n-Hexane
- Chloroform
- Ethanol
- Carbon tetrachloride
Correct Answer: Ethanol
Q7. The critical temperature and pressure of CO2 (rounded) are approximately:
- 0°C and 1 bar
- 31°C and 74 bar
- 100°C and 1 bar
- 200°C and 200 bar
Correct Answer: 31°C and 74 bar
Q8. A main limitation of routine implementation of SFE in many labs is:
- Inability to extract nonpolar compounds
- High capital and equipment cost for high-pressure systems
- Excessive use of toxic organic solvents
- Incompatibility with temperature-sensitive compounds
Correct Answer: High capital and equipment cost for high-pressure systems
Q9. Which solvent property most strongly affects microwave-assisted extraction efficiency?
- Boiling point only
- Dielectric constant and loss factor (ability to absorb microwaves)
- Viscosity exclusively
- Color and odor
Correct Answer: Dielectric constant and loss factor (ability to absorb microwaves)
Q10. Which principle aligns with “green extraction” in pharmaceutical practice?
- Maximize use of halogenated solvents for efficiency
- Reduce solvent consumption, energy use and waste generation
- Prioritize yield without regard to toxicity
- Use single-use disposables for every extraction
Correct Answer: Reduce solvent consumption, energy use and waste generation
Q11. Pressurized liquid extraction (PLE) is also commonly known as:
- Hydrodistillation
- Accelerated solvent extraction (ASE)
- Soxhlet extraction
- Steam volatilization
Correct Answer: Accelerated solvent extraction (ASE)
Q12. Which extraction method is especially suitable for heat-labile, nonpolar compounds requiring low-temperature processing?
- Hydrodistillation at high temperature
- Supercritical fluid extraction (SFE) with CO2
- Soxhlet with refluxing solvent for many hours
- Direct combustion for sample cleanup
Correct Answer: Supercritical fluid extraction (SFE) with CO2
Q13. The distribution coefficient (D) differs from the partition coefficient (K) because D:
- Is measured only at 100°C
- Accounts for all chemical forms (ionized + unionized) of a compound between phases
- Is irrelevant in extraction design
- Refers to solvent density ratio
Correct Answer: Accounts for all chemical forms (ionized + unionized) of a compound between phases
Q14. Reducing the particle size of plant material generally affects extraction by:
- Decreasing surface area and slowing extraction
- Increasing surface area and enhancing mass transfer rate
- Changing solvent polarity
- Converting analytes to other chemical forms
Correct Answer: Increasing surface area and enhancing mass transfer rate
Q15. In SFE, a small percentage of ethanol is often used as a co-solvent because it:
- Decreases the solvent polarity further
- Acts as a polar modifier to improve extraction of polar analytes
- Reacts chemically with CO2 to form carbamates
- Rigidifies the supercritical phase making it less effective
Correct Answer: Acts as a polar modifier to improve extraction of polar analytes
Q16. Which extraction technique is traditionally best for volatile essential oils prior to GC analysis?
- Hydrodistillation (steam distillation)
- Supercritical fluid extraction with water
- Solid-phase microextraction at 500°C
- Direct injection of raw plant powder into GC
Correct Answer: Hydrodistillation (steam distillation)
Q17. A primary safety concern when performing conventional solvent extraction in the lab is:
- Excessive nutritional content of extracts
- Flammability and toxicity of organic solvents
- Lack of extractable compounds in samples
- Too much water formation
Correct Answer: Flammability and toxicity of organic solvents
Q18. Which ICH guideline addresses permissible levels of residual solvents in pharmaceuticals?
- ICH Q1A
- ICH Q3C
- ICH Q7
- ICH M4
Correct Answer: ICH Q3C
Q19. In SFE with CO2, increasing pressure at constant temperature generally:
- Decreases solvent density and reduces solubility
- Increases solvent density and often increases solubility of solutes
- Has no effect on solvating power
- Always causes chemical degradation of analytes
Correct Answer: Increases solvent density and often increases solubility of solutes
Q20. Which modern extraction method typically provides the fastest extraction kinetics for many matrices?
- Conventional maceration over days
- Microwave-assisted extraction (MAE)
- Slow Soxhlet extraction overnight
- Hydrodistillation lasting many hours
Correct Answer: Microwave-assisted extraction (MAE)
Q21. How can selectivity for an ionizable drug be improved during liquid-liquid extraction?
- By adjusting pH to convert the drug to its preferred ionization state
- By using only nonpolar solvents regardless of drug chemistry
- By increasing particle size of the sample
- By avoiding any solvent choice
Correct Answer: By adjusting pH to convert the drug to its preferred ionization state
Q22. Which solvent is generally considered least “green” among the choices below?
- Ethyl acetate
- Supercritical CO2
- Dichloromethane (methylene chloride)
- Water
Correct Answer: Dichloromethane (methylene chloride)
Q23. Which analytical technique is most commonly used to quantify and assess purity of small-molecule extracts?
- High-performance liquid chromatography (HPLC)
- Optical microscopy only
- Gravimetric analysis without separation
- Visual colorimetry exclusively
Correct Answer: High-performance liquid chromatography (HPLC)
Q24. Log P (partition coefficient) is primarily used to predict a compound’s:
- Melting point
- Lipophilicity and membrane permeability
- Spectral absorbance in UV only
- Boiling point at atmospheric pressure
Correct Answer: Lipophilicity and membrane permeability
Q25. In a Soxhlet extractor, the solvent is repeated condensed and returned to the sample; the primary purpose of this reflux is to:
- Maintain a constant high pressure in the system
- Provide continuous extraction with fresh warm solvent without manual solvent changes
- Convert solutes into gaseous products
- Remove water from the sample by combustion
Correct Answer: Provide continuous extraction with fresh warm solvent without manual solvent changes
Q26. Which approach is commonly used to scale up microwave-assisted extraction for industrial processing?
- Simply increasing batch size in the same domestic microwave
- Using continuous-flow microwave reactors designed for controlled penetration and heating
- Switching to hydrodistillation as the only scale-up route
- Removing solvent and heating sample directly to 400°C
Correct Answer: Using continuous-flow microwave reactors designed for controlled penetration and heating
Q27. During SFE of a polar target compound using neat CO2, which change would likely decrease extraction yield?
- Adding a small percentage of ethanol as co-solvent
- Increasing pressure to raise CO2 density
- Using too low pressure so CO2 density is insufficient
- Optimizing extraction time to equilibrium
Correct Answer: Using too low pressure so CO2 density is insufficient
Q28. To extract basic alkaloids from plant material into an organic solvent, you should first:
- Acidify the matrix to form water-soluble salts
- Basify the matrix to convert alkaloids to their free base form
- Oxidize the alkaloids chemically
- Dry the sample at 300°C
Correct Answer: Basify the matrix to convert alkaloids to their free base form
Q29. Which metric is commonly used to evaluate and compare extraction efficiency between methods?
- Total extraction yield (percent of analyte recovered)
- Number of colors observed in the extract
- Size of the extraction apparatus only
- Time of day when extraction is performed
Correct Answer: Total extraction yield (percent of analyte recovered)
Q30. For laboratory extraction of highly polar, heat-sensitive phenolic glycosides with minimal solvent residues, a recommended modern approach is:
- Prolonged Soxhlet extraction with hexane
- Pressurized liquid extraction (PLE/ASE) with polar solvent at controlled moderate temperatures
- Direct combustion to ash followed by solventless analysis
- Hydrodistillation at vigorous boiling
Correct Answer: Pressurized liquid extraction (PLE/ASE) with polar solvent at controlled moderate temperatures
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