CE characteristics and principles MCQs With Answer

Introduction: Capillary electrophoresis (CE) characteristics and principles MCQs With Answer is designed for M.Pharm students aiming to master the theoretical foundations and practical considerations of CE as applied in pharmaceutical analysis. This concise question set emphasizes core principles—electrophoretic mobility, electroosmotic flow, separation modes (CZE, MEKC, IEF, ITP), sample preconcentration, detection techniques, capillary surface chemistry, and thermal effects—along with troubleshooting and instrumentation aspects. Each question probes deeper conceptual understanding and analytical implications, helping students prepare for exams and lab work by reinforcing the mechanisms that govern resolution, sensitivity, reproducibility, and CE–MS interfacing in drug analysis and biomolecule separations.

Q1. What is the primary physical basis for separation of analytes in capillary electrophoresis?

• Partitioning between a stationary phase and mobile phase
• Differences in electrophoretic mobility under an electric field
• Differences in volatility leading to differential boiling
• Size exclusion through a porous stationary bed

Correct Answer: Differences in electrophoretic mobility under an electric field

Q2. In an uncoated fused-silica capillary at typical pH, which direction does electroosmotic flow (EOF) carry the bulk solution?

• Toward the anode because the wall is positively charged
• Toward the cathode because the wall is negatively charged
• From high electric field to low electric field regions irrespective of polarity
• No net bulk flow occurs in CE

Correct Answer: Toward the cathode because the wall is negatively charged

Q3. Electrophoretic mobility of an ion is most directly governed by which of the following relationships?

• Proportional to ion mass and inversely to applied voltage
• Proportional to ion charge and inversely to hydrodynamic friction (size/viscosity)
• Proportional to ionic radius squared and independent of buffer viscosity
• Determined solely by the capillary inner diameter

Correct Answer: Proportional to ion charge and inversely to hydrodynamic friction (size/viscosity)

Q4. Which of the following is a major analytical advantage of CE compared with many chromatographic methods?

• Large sample volumes are required for good sensitivity
• High separation efficiency with extremely low sample consumption
• Separation is independent of buffer pH and ionic strength
• Permanent stationary phases provide retention-based selectivity

Correct Answer: High separation efficiency with extremely low sample consumption

Q5. Increasing the applied electric field in CE typically results in which combined effect?

• Lower analysis speed and reduced Joule heating
• Improved resolution with no thermal consequences
• Faster separation but increased Joule heating and potential band broadening
• Complete elimination of electroosmotic flow

Correct Answer: Faster separation but increased Joule heating and potential band broadening

Q6. Which CE mode employs surfactant micelles to enable separation of neutral and charged solutes?

• Capillary zone electrophoresis (CZE)
• Micellar electrokinetic chromatography (MEKC)
• Isoelectric focusing (IEF)
• Isotachophoresis (ITP)

Correct Answer: Micellar electrokinetic chromatography (MEKC)

Q7. Isoelectric focusing (IEF) separates amphoteric molecules primarily according to which property?

• Molecular mass under denaturing conditions
• Partition coefficient into micelles
• Isoelectric point (pI) within a pH gradient
• Hydrodynamic radius in nonaqueous solvents

Correct Answer: Isoelectric point (pI) within a pH gradient

Q8. Why are capillary inner-surface coatings used in CE for protein analysis?

• To increase electroosmotic flow and accelerate elution of proteins
• To generate a stationary phase for reversed-phase interactions
• To reduce protein adsorption to silica and control EOF for reproducible separations
• To make the capillary opaque for certain detectors

Correct Answer: To reduce protein adsorption to silica and control EOF for reproducible separations

Q9. Which ionization/detection technique is most commonly used for direct coupling of CE to mass spectrometry?

• Inductively coupled plasma (ICP) ionization
• Atmospheric pressure chemical ionization (APCI)
• Electrospray ionization (ESI)
• Flame ionization detector (FID)

Correct Answer: Electrospray ionization (ESI)

Q10. Which sample preconcentration method in CE relies on creating a low-conductivity sample zone to amplify the electric field within the sample plug?

• On-line dialysis concentration
• Field-amplified sample stacking (FASS)
• Plate height reduction via coating
• Temperature gradient focusing

Correct Answer: Field-amplified sample stacking (FASS)

Q11. Joule heating in CE increases directly with which of the following buffer/electrical parameters?

• Applied electric field strength and electrolyte conductivity
• Capillary length only, independent of voltage
• Detector sensitivity
• Analyte pKa values exclusively

Correct Answer: Applied electric field strength and electrolyte conductivity

Q12. Why does CE often achieve much higher theoretical plate counts than many HPLC separations?

• Because CE uses packed stationary phases that reduce band broadening
• Because CE zones experience plug-like flow with minimal mass transfer dispersion
• Because capillaries are operated at extremely low temperatures only
• Because CE uses higher sample volumes which reduce diffusion

Correct Answer: Because CE zones experience plug-like flow with minimal mass transfer dispersion

Q13. Which buffer parameter most directly influences the magnitude of electroosmotic flow (EOF) in bare silica capillaries?

• Buffer color
• pH of the background electrolyte (affecting silanol ionization)
• Ambient humidity only
• Capillary outer coating material

Correct Answer: pH of the background electrolyte (affecting silanol ionization)

Q14. What is the principal practical advantage of dynamic capillary coatings compared with covalent capillary coatings?

• Dynamic coatings are permanent and require no regeneration
• Dynamic coatings are easier to apply and can be regenerated between runs
• Dynamic coatings eliminate the need for any buffer control
• Dynamic coatings increase EOF to maximum values always

Correct Answer: Dynamic coatings are easier to apply and can be regenerated between runs

Q15. Contactless conductivity detection in CE is typically characterized by which property?

• Highest sensitivity and selectivity for trace organics
• Universal response for ionic species but generally lower sensitivity than LIF
• Requires derivatization of neutral analytes for detection
• Is incompatible with aqueous buffers

Correct Answer: Universal response for ionic species but generally lower sensitivity than LIF

Q16. Isotachophoresis (ITP) separates ions by which fundamental mechanism?

• Partitioning into a stationary liquid phase
• Formation of discrete, focused zones between leading and terminating electrolytes based on ionic mobility
• Separation solely by molecular weight under denaturing conditions
• Ionization of analytes at the detector

Correct Answer: Formation of discrete, focused zones between leading and terminating electrolytes based on ionic mobility

Q17. Precise capillary temperature control in CE is essential primarily because:

• Temperature has negligible effect on separation reproducibility
• It minimizes viscosity and mobility changes caused by Joule heating, improving reproducibility and efficiency
• It prevents capillary wall from melting
• It changes analyte pKa to fixed values irrespective of buffer

Correct Answer: It minimizes viscosity and mobility changes caused by Joule heating, improving reproducibility and efficiency

Q18. Laser-induced fluorescence (LIF) detection in CE is most advantageous when:

• Analytes are nonpolar and lack chromophores
• Analytes are intrinsically fluorescent or can be derivatized with a fluorescent tag for highest sensitivity
• Only ionic strength information is required
• A universal, label-free detection is mandatory

Correct Answer: Analytes are intrinsically fluorescent or can be derivatized with a fluorescent tag for highest sensitivity

Q19. Which source of band broadening is typically dominant in CE and therefore commonly considered in CE theory?

• Eddy diffusion caused by packed particles
• Longitudinal diffusion of analyte zones during migration
• Interphase mass transfer between mobile and stationary phases
• Mechanical vibration of capillary fittings

Correct Answer: Longitudinal diffusion of analyte zones during migration

Q20. Why does introducing a low-conductivity sample plug into a higher-conductivity background electrolyte enable sample stacking?

• Because it reduces the capillary temperature dramatically
• Because the lower conductivity zone raises the local electric field in the sample plug, causing analytes to migrate faster and compress into narrow zones at the boundary
• Because low conductivity destroys electroosmotic flow entirely
• Because it creates a stationary phase in the capillary lumen

Correct Answer: Because the lower conductivity zone raises the local electric field in the sample plug, causing analytes to migrate faster and compress into narrow zones at the boundary

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