Adsorption chromatography is a core separation technique in pharmaceutical analysis that relies on the interaction between analytes and a solid adsorbent stationary phase such as silica or alumina. B.Pharm students should understand methodology elements—adsorbent selection, mobile phase polarity, column packing, elution techniques, and adsorption isotherms (Langmuir, Freundlich)—along with performance metrics like retention, selectivity, and efficiency. This topic covers advantages (simplicity, high resolution for polar compounds), limitations (sensitivity to moisture, limited for nonpolar analytes, scaling challenges), and diverse applications in drug purification, impurity profiling, and TLC/column analyses. Keywords: adsorption chromatography, adsorbent, stationary phase, mobile phase, elution, retention, applications. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What is the primary mechanism of separation in adsorption chromatography?
- Partitioning between two liquid phases
- Size exclusion based on molecular weight
- Adsorption of analytes onto a solid stationary phase
- Electrophoretic migration under an electric field
Correct Answer: Adsorption of analytes onto a solid stationary phase
Q2. Which of the following materials is most commonly used as an adsorbent in adsorption chromatography?
- Polystyrene-divinylbenzene
- Silica gel
- Cellulose acetate
- Polyethylene glycol
Correct Answer: Silica gel
Q3. In adsorption chromatography, increasing the polarity of the mobile phase typically results in which effect for normal-phase silica chromatography?
- Stronger retention of polar analytes
- Faster elution of polar analytes
- No change in retention
- Stronger retention of nonpolar analytes
Correct Answer: Faster elution of polar analytes
Q4. Which adsorption isotherm is often used to describe monolayer adsorption on a homogeneous surface?
- Freundlich isotherm
- Langmuir isotherm
- BET isotherm
- Henry’s law
Correct Answer: Langmuir isotherm
Q5. Thin-layer chromatography (TLC) is an example of which form of adsorption chromatography?
- Gas adsorption chromatography
- Preparative reversed-phase chromatography
- Planar adsorption chromatography
- Ion-exchange chromatography
Correct Answer: Planar adsorption chromatography
Q6. Which factor does NOT significantly affect adsorption chromatography separations?
- Particle size of the adsorbent
- Temperature of the column
- pH of mobile phase when analytes are neutral
- Polarity of the mobile phase
Correct Answer: pH of mobile phase when analytes are neutral
Q7. What does the retention factor (k) in chromatography indicate?
- The ratio of solute in stationary phase to mobile phase at equilibrium
- The flow rate of the mobile phase
- The pore volume of the adsorbent
- The plate height of the column
Correct Answer: The ratio of solute in stationary phase to mobile phase at equilibrium
Q8. Which mobile phase strategy is commonly used to improve resolution in adsorption column chromatography?
- Changing column diameter only
- Gradient elution by increasing mobile phase polarity
- Decreasing injector temperature
- Using a single nonpolar solvent throughout
Correct Answer: Gradient elution by increasing mobile phase polarity
Q9. For adsorption chromatography on alumina, which class of compounds is typically retained more strongly?
- Nonpolar hydrocarbons
- Polar compounds with hydrogen bonding capability
- Large proteins
- Inert gases
Correct Answer: Polar compounds with hydrogen bonding capability
Q10. In TLC, what does a high Rf value indicate about an analyte?
- It is strongly adsorbed to the stationary phase
- It migrated far and has relatively weak adsorption
- It decomposed during development
- It is highly polar and tightly bound
Correct Answer: It migrated far and has relatively weak adsorption
Q11. Which of these is an advantage of adsorption chromatography in pharmaceutical labs?
- Insensitive to moisture and water in solvents
- High resolution for polar small molecules
- No need for method development
- Universal suitability for proteins and nucleic acids
Correct Answer: High resolution for polar small molecules
Q12. What is a common disadvantage of adsorption chromatography compared with reversed-phase methods?
- Lower sensitivity for polar analytes
- Greater sensitivity to moisture and solvent impurities
- Inability to separate isomers
- Requires high-temperature operation
Correct Answer: Greater sensitivity to moisture and solvent impurities
Q13. Which preparative technique uses adsorption chromatography principles for isolating larger drug quantities?
- Preparative gas chromatography
- Preparative column chromatography with silica or alumina
- Capillary electrophoresis
- Size-exclusion ultrafiltration
Correct Answer: Preparative column chromatography with silica or alumina
Q14. Breakthrough in adsorption columns refers to:
- The start of gradient elution
- The point when analyte begins to appear in the column effluent
- The change in mobile phase viscosity
- Complete degradation of the adsorbent
Correct Answer: The point when analyte begins to appear in the column effluent
Q15. What is a typical role of added polar modifiers (e.g., methanol) in the mobile phase for normal-phase adsorption chromatography?
- To increase stationary phase surface area
- To decrease eluent strength and slow elution
- To increase eluent strength and promote desorption of polar analytes
- To polymerize the adsorbent surface
Correct Answer: To increase eluent strength and promote desorption of polar analytes
Q16. Column efficiency in adsorption chromatography is often expressed in terms of:
- Retention factor (Rf)
- Theoretical plates (N)
- Adsorbent pore diameter alone
- Detector wavelength
Correct Answer: Theoretical plates (N)
Q17. Which peak shape issue commonly arises from strong adsorption sites and slow desorption?
- Gaussian sharpening
- Peak tailing
- Peak fronting
- Split peaks
Correct Answer: Peak tailing
Q18. How does decreasing adsorbent particle size typically affect chromatographic performance?
- Decreases column backpressure but reduces resolution
- Increases band broadening due to eddy diffusion
- Increases efficiency and resolution but increases backpressure
- Has no effect on retention or efficiency
Correct Answer: Increases efficiency and resolution but increases backpressure
Q19. Which analytical application commonly uses adsorption chromatography for impurity profiling in drug substances?
- Mass spectrometry without prior separation
- Preparative crystallization only
- Thin-layer chromatography and silica column assays
- Turbidimetric analysis
Correct Answer: Thin-layer chromatography and silica column assays
Q20. In adsorption chromatography, what is meant by ‘eluent strength’?
- The mechanical strength of the column packing
- The ability of the mobile phase to displace analytes from the stationary phase
- The ionic strength of buffer solutions only
- The retention capacity of the adsorbent
Correct Answer: The ability of the mobile phase to displace analytes from the stationary phase
Q21. When scaling up an adsorption chromatography method from analytical to preparative scale, which parameter often requires careful adjustment?
- Detector wavelength
- Adsorbent particle chemistry only
- Flow rate and column dimensions
- Ambient room color
Correct Answer: Flow rate and column dimensions
Q22. Which solvent system would you choose to elute a highly polar drug from a silica column most effectively?
- Hexane alone
- Hexane with increasing proportion of ethyl acetate or methanol
- Pure nonpolar aromatic solvent like toluene only
- Dry nitrogen gas
Correct Answer: Hexane with increasing proportion of ethyl acetate or methanol
Q23. Which chromatographic metric directly measures the separation between two adjacent peaks?
- Retention factor (k)
- Resolution (Rs)
- Plate height (H)
- Adsorbent porosity
Correct Answer: Resolution (Rs)
Q24. Adsorption chromatography is least suitable for which class of molecules without modification?
- Small polar pharmaceuticals
- Nonpolar volatile hydrocarbons
- High molecular weight proteins
- Neutral organic dyes
Correct Answer: High molecular weight proteins
Q25. Which practice helps reduce peak tailing caused by active silanol groups on silica?
- Using lower purity solvents
- Derivatizing or end-capping the silica surface
- Reducing column length drastically
- Increasing sample concentration without changing mobile phase
Correct Answer: Derivatizing or end-capping the silica surface
Q26. In adsorption chromatography, Freundlich isotherm best describes adsorption that is:
- Limited to a monolayer on homogeneous surface
- Multilayer and on heterogeneous surfaces with non-uniform energy sites
- Only applicable to gas phase adsorption
- Independent of concentration
Correct Answer: Multilayer and on heterogeneous surfaces with non-uniform energy sites
Q27. Which detector is commonly coupled with adsorption-based column separations in analytical labs for qualitative and quantitative analysis?
- Refractive index detector only for all analytes
- UV-Vis detector or mass spectrometer depending on analyte
- Thermal conductivity detector (TCD) only
- Flame ionization detector for aqueous eluents
Correct Answer: UV-Vis detector or mass spectrometer depending on analyte
Q28. What is a recommended sample preparation step before loading onto an adsorption column to improve separation?
- Load the crude bulk without filtration to save time
- Filter and remove particulates; dissolve sample in a solvent compatible with the starting mobile phase
- Dry the sample completely to a powder and load neat
- Add salts to precipitate analytes directly on the column
Correct Answer: Filter and remove particulates; dissolve sample in a solvent compatible with the starting mobile phase
Q29. Which troubleshooting step should be taken if peaks elute very slowly despite correct solvent polarity?
- Replace detector lamp immediately
- Check for column blockage, old adsorbent, or excessive adsorbent-water interactions
- Increase sample injection volume without changing flow
- Switch to a weaker adsorbent like charcoal
Correct Answer: Check for column blockage, old adsorbent, or excessive adsorbent-water interactions
Q30. A key pharmaceutical application of adsorption chromatography is:
- Measuring ambient air pressure
- Isolation and purification of synthetic intermediates and active pharmaceutical ingredients (APIs)
- Sterilizing injectable formulations
- Determining tablet hardness
Correct Answer: Isolation and purification of synthetic intermediates and active pharmaceutical ingredients (APIs)
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