Electrophoresis – basic concepts and electrophoretic mobility MCQs With Answer

Electrophoresis – basic concepts and electrophoretic mobility MCQs With Answer

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Electrophoresis – basic concepts and electrophoretic mobility MCQs With Answer

Electrophoresis is a core analytical technique in pharmaceutical sciences used for separation and characterization of charged biomolecules. B.Pharm students should understand electrophoretic mobility, electric field effects, buffer selection, zeta potential, and gel matrices like agarose and polyacrylamide. Key concepts include mobility (µ = v/E), electroosmotic flow, sieving, ionic strength, pH-dependent charge, and instrumental factors such as capillary electrophoresis and Joule heating. Mastery of these fundamentals supports drug analysis, protein purity assessment, and method development. This set covers theory, calculations, instrumentation, and practical considerations to build strong analytical competence. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is the definition of electrophoretic mobility?

  • The distance a particle migrates per unit time
  • The velocity of a particle divided by the applied electric field
  • The net charge on a molecule at a given pH
  • The strength of the buffer used in electrophoresis

Correct Answer: The velocity of a particle divided by the applied electric field

Q2. Which equation directly expresses electrophoretic mobility (µ)?

  • µ = q × r
  • µ = v × E
  • µ = v / E
  • µ = E / v

Correct Answer: µ = v / E

Q3. In Henry’s equation relating mobility to zeta potential, which parameter represents fluid viscosity?

  • ζ (zeta potential)
  • ε (dielectric constant)
  • η (eta)
  • f(κa) (Henry function)

Correct Answer: η (eta)

Q4. Which of the following factors decreases electrophoretic mobility of a charged spherical particle?

  • Increasing electric field strength
  • Decreasing medium viscosity
  • Increasing particle radius
  • Increasing particle charge

Correct Answer: Increasing particle radius

Q5. Electroosmotic flow (EOF) in capillary electrophoresis is caused primarily by:

  • Applied magnetic field
  • Neutral particles migrating under gravity
  • Movement of solvent caused by charged capillary walls
  • Heat convection from Joule heating

Correct Answer: Movement of solvent caused by charged capillary walls

Q6. Which gel matrix is most suitable for separating large DNA fragments?

  • Polyacrylamide gel
  • Agarose gel
  • SDS-PAGE
  • Isoelectric focusing gel

Correct Answer: Agarose gel

Q7. SDS-PAGE separates proteins primarily on the basis of:

  • Native charge and conformation
  • Isoelectric point
  • Molecular size (mass)
  • Hydrophobicity

Correct Answer: Molecular size (mass)

Q8. Which statement about isoelectric focusing (IEF) is true?

  • Proteins are separated by molecular weight
  • Proteins migrate to their isoelectric point and stop
  • IED uses SDS to denature proteins
  • IEF relies on sieving through a gel matrix

Correct Answer: Proteins migrate to their isoelectric point and stop

Q9. A particle moves at 0.2 cm/s in an electric field of 10 V/cm. What is its electrophoretic mobility?

  • 0.2 cm^2/(V·s)
  • 0.02 cm^2/(V·s)
  • 2.0 cm^2/(V·s)
  • 0.0002 cm^2/(V·s)

Correct Answer: 0.02 cm^2/(V·s)

Q10. Which buffer property most strongly influences protein charge during electrophoresis?

  • Buffer ionic strength
  • Buffer pH
  • Buffer color
  • Buffer viscosity

Correct Answer: Buffer pH

Q11. Joule heating in electrophoresis results from:

  • Light absorption by stains
  • Conversion of electrical energy into heat due to current flow
  • Friction between gel matrix and molecules
  • Cooling systems in the apparatus

Correct Answer: Conversion of electrical energy into heat due to current flow

Q12. Which technique provides the highest resolution for small proteins and peptides?

  • Agarose gel electrophoresis
  • Native PAGE
  • Polyacrylamide gel electrophoresis (PAGE)
  • Paper electrophoresis

Correct Answer: Polyacrylamide gel electrophoresis (PAGE)

Q13. In capillary electrophoresis, reducing the capillary inner diameter primarily reduces:

  • Electroosmotic flow
  • Sample injection volume only
  • Joule heating and improves separation efficiency
  • Electrophoretic mobility of analytes

Correct Answer: Joule heating and improves separation efficiency

Q14. Which factor does NOT significantly affect electrophoretic mobility of ions?

  • Charge of the ion
  • Size of the ion
  • Applied electric field direction
  • Color of the ion

Correct Answer: Color of the ion

Q15. Zeta potential is most closely related to which electrophoretic property?

  • Migration distance in gel
  • Electrophoretic mobility
  • Optical absorbance
  • Molecular weight

Correct Answer: Electrophoretic mobility

Q16. Which detection method is commonly coupled with capillary electrophoresis for pharmaceuticals?

  • Mass spectrometry (CE-MS)
  • Flame ionization detector
  • NMR spectroscopy inline
  • Infrared imaging

Correct Answer: Mass spectrometry (CE-MS)

Q17. During native electrophoresis, proteins retain:

  • Their tertiary structure and native charge
  • Uniform negative charge from SDS
  • Only primary sequence information
  • No biological activity

Correct Answer: Their tertiary structure and native charge

Q18. Which statement about sieving in gel electrophoresis is correct?

  • Sieving is independent of gel pore size
  • Smaller pores create greater size-based separation
  • Sieving only affects charged particles with identical mass
  • Sieving accelerates migration of large molecules

Correct Answer: Smaller pores create greater size-based separation

Q19. In two-dimensional (2D) electrophoresis, the first dimension typically separates proteins by:

  • Molecular weight
  • Hydrophobicity
  • Isoelectric point (pI)
  • Staining affinity

Correct Answer: Isoelectric point (pI)

Q20. Which parameter should be minimized to reduce band broadening in electrophoresis?

  • Electric field strength
  • Temperature gradients (Joule heating)
  • Buffer capacity
  • Sample purity

Correct Answer: Temperature gradients (Joule heating)

Q21. Isotachophoresis is a technique where analytes are separated based on:

  • Constant velocity between leading and terminating ions
  • Migration in a gel gradient
  • Differences in UV absorbance only
  • Random diffusion

Correct Answer: Constant velocity between leading and terminating ions

Q22. Which staining method is most sensitive for protein detection after PAGE?

  • Coomassie Brilliant Blue
  • SDS stain
  • Silver staining
  • Ponceau S

Correct Answer: Silver staining

Q23. Which of these will increase electroosmotic flow in fused silica capillaries?

  • Lower pH to protonate silanol groups
  • Coating the capillary with neutral polymer
  • Increasing pH to deprotonate silanol groups
  • Adding organic solvent to the buffer

Correct Answer: Increasing pH to deprotonate silanol groups

Q24. Which practice helps reduce sample heating and maintain resolution during high-voltage electrophoresis?

  • Using higher ionic strength buffer
  • Increasing sample load dramatically
  • Using thinner gels or capillaries with cooling
  • Removing buffer during run

Correct Answer: Using thinner gels or capillaries with cooling

Q25. During electrophoresis, a protein with pI 6.0 in a buffer pH 8.0 will be:

  • Positively charged
  • Negatively charged
  • Neutral and immobile
  • Denatured by pH

Correct Answer: Negatively charged

Q26. Which of the following is a major advantage of capillary electrophoresis over slab-gel electrophoresis?

  • Lower separation efficiency
  • Higher sample consumption
  • Faster analysis with high efficiency and automation
  • No need for buffer

Correct Answer: Faster analysis with high efficiency and automation

Q27. In electrophoretic mobility measurement, increasing ionic strength of the buffer generally:

  • Increases mobility by increasing charge
  • Decreases mobility due to charge screening
  • Has no effect on mobility
  • Changes mobility unpredictably

Correct Answer: Decreases mobility due to charge screening

Q28. Which term describes the phenomenon where molecules of similar charge separate due to differences in size during electrophoresis?

  • Electroosmosis
  • Sieving
  • Isoelectric focusing
  • Electrolysis

Correct Answer: Sieving

Q29. A researcher observes trailing and diffuse bands; which is the most likely cause?

  • Optimal buffer composition
  • Overloading the sample or poor sample stacking
  • Appropriate gel concentration
  • Using freshly prepared buffers

Correct Answer: Overloading the sample or poor sample stacking

Q30. Which best describes the relationship between zeta potential and colloidal stability relevant to electrophoresis?

  • Low absolute zeta potential increases colloidal stability
  • High absolute zeta potential promotes aggregation
  • High absolute zeta potential increases electrostatic repulsion and stability
  • Zeta potential does not affect colloidal interactions

Correct Answer: High absolute zeta potential increases electrostatic repulsion and stability

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