Basic CE configuration MCQs With Answer

Introduction: This blog presents a focused set of multiple-choice questions on Basic Capillary Electrophoresis (CE) configurations tailored for M.Pharm students studying Advanced Instrumental Analysis (MPA 201T). The questions emphasize practical and theoretical aspects of CE set-ups, including capillary types, EOF control, injection techniques, detectors, CE–MS interfaces, coating strategies, stacking methods, and troubleshooting. Designed to deepen conceptual understanding and aid exam preparation, each MCQ explores parameters that influence resolution, sensitivity, and reproducibility in CE separations. Answers are provided to support self-assessment and reinforce learning for application in pharmaceutical analysis, method development, and instrumental optimization.

Q1. Which CE configuration is most appropriate for separating small neutral molecules by using surfactant micelles as a pseudo-stationary phase?

• Capillary zone electrophoresis (CZE)
• Capillary gel electrophoresis (CGE)
• Micellar electrokinetic chromatography (MEKC)
• Isotachophoresis (ITP)

Correct Answer: Micellar electrokinetic chromatography (MEKC)

Q2. In a CE–MS system, which interface provides the best compromise between ease of use and robustness for routine pharmaceutical analysis?

• Sheathless porous tip interface
• Sheath-flow (coaxial) electrospray interface
• Direct capillary outlet into vacuum without sheath
• Atmospheric pressure chemical ionization (APCI) interface

Correct Answer: Sheath-flow (coaxial) electrospray interface

Q3. Which injection technique in CE is most influenced by differences in sample and background electrolyte conductivity?

• Hydrodynamic (pressure) injection
• Electrokinetic injection
• Hydrodynamic long-time stacking
• Gel plug injection

Correct Answer: Electrokinetic injection

Q4. What is the primary reason to choose a narrower inner diameter (i.d.) capillary (e.g., 25–50 μm) in high-voltage CE separations?

• To increase sample capacity and loading volume
• To reduce Joule heating and improve heat dissipation
• To decrease migration times for all analytes
• To eliminate the need for a detector

Correct Answer: To reduce Joule heating and improve heat dissipation

Q5. Which capillary coating type is most suitable when you need long-term suppression of electroosmotic flow (EOF) and minimize protein adsorption?

• Dynamic coating with surfactant (e.g., SDS)
• Covalent neutral polymer coating (e.g., polyacrylamide)
• Uncoated bare fused silica
• Temporary coating with organic solvent

Correct Answer: Covalent neutral polymer coating (e.g., polyacrylamide)

Q6. Field-amplified sample stacking relies on which of the following key principles?

• Using a high-conductivity sample in a low-conductivity buffer
• Injecting sample in a low-conductivity medium into a higher-conductivity background electrolyte
• Using micelles to sweep analytes into a narrow band
• Imposing a temperature gradient along the capillary

Correct Answer: Injecting sample in a low-conductivity medium into a higher-conductivity background electrolyte

Q7. In CE, reversing the polarity of the applied voltage while keeping the same buffer pH is typically done to:

• Change the direction of EOF to drive analytes toward the detector
• Increase Joule heating to speed separations
• Convert MEKC into CZE separation mode
• Allow non-aqueous buffers to be used

Correct Answer: Change the direction of EOF to drive analytes toward the detector

Q8. Which additive is commonly used in CE to impart chiral selectivity for enantiomer separations?

• Sodium dodecyl sulfate (SDS)
• Beta-cyclodextrin (β-CD) or derivatized cyclodextrins
• Urea
• Trifluoroacetic acid (TFA)

Correct Answer: Beta-cyclodextrin (β-CD) or derivatized cyclodextrins

Q9. When coupling CE to mass spectrometry, why might a sheathless porous tip be chosen over a sheath-flow interface?

• Because it increases robustness and allows higher flow rates
• Because it typically provides superior sensitivity due to minimal dilution
• Because it is easier to fabricate and replace than sheath-flow
• Because it completely eliminates electric field requirements

Correct Answer: Because it typically provides superior sensitivity due to minimal dilution

Q10. What is the main effect of increasing buffer ionic strength on electrophoretic mobility and EOF in a CE separation?

• EOF increases and analyte mobilities become independent of ionic strength
• EOF decreases due to double layer compression; ionic strength can reduce electrophoretic resolution
• EOF reverses direction and electrophoretic mobility increases dramatically
• No effect on EOF, but conductivity decreases

Correct Answer: EOF decreases due to double layer compression; ionic strength can reduce electrophoretic resolution

Q11. Which mode of CE is preferred for high-molecular-weight biomolecules like DNA or proteins where sieving is required?

• Capillary zone electrophoresis (CZE)
• Micellar electrokinetic chromatography (MEKC)
• Capillary gel electrophoresis (CGE)
• Isotachophoresis (ITP)

Correct Answer: Capillary gel electrophoresis (CGE)

Q12. In transient isotachophoresis (tITP) stacking, which statement best describes the configuration needed?

• Sample is placed in a high-conductivity trailing electrolyte surrounded by low-conductivity leading electrolyte
• Sample is introduced between a leading electrolyte (higher mobility) and trailing electrolyte (lower mobility) to concentrate analytes
• Sample and buffer ionic strengths are matched to prevent stacking
• tITP requires micellar phases for stacking to occur

Correct Answer: Sample is introduced between a leading electrolyte (higher mobility) and trailing electrolyte (lower mobility) to concentrate analytes

Q13. Which detector is most commonly used for routine quantitation in pharmaceutical CE due to broad applicability and simplicity?

• Laser-induced fluorescence (LIF)
Mass spectrometry (MS)
• UV-absorbance (on-capillary) detector
• Electrochemical detector

Correct Answer: UV-absorbance (on-capillary) detector

Q14. Which strategy is most effective to reduce band broadening caused by Joule heating during high-voltage CE runs?

• Using wider capillaries and increasing applied voltage
• Reducing capillary i.d., improving thermostating, and lowering current (buffer ionic strength)
• Removing buffer and running in dry capillary mode
• Increasing buffer viscosity with glycerol to eliminate EOF

Correct Answer: Reducing capillary i.d., improving thermostating, and lowering current (buffer ionic strength)

Q15. For samples containing high concentrations of inorganic salts, which CE–MS interface approach aids in minimizing signal suppression?

• Direct infusion without desolvation
• Sheath-flow interface with optimized sheath liquid composition and flow rate
• Using only UV detection to avoid MS issues
• Increasing sample injection time without cleanup

Correct Answer: Sheath-flow interface with optimized sheath liquid composition and flow rate

Q16. Dynamic coating of a capillary with polybrene (a cationic polymer) will most likely produce which effect on EOF and analyte interaction?

• Create a negatively charged surface and increase EOF toward cathode
• Create a positively charged surface, reverse or reduce EOF, and reduce adsorption of acidic analytes
• Completely eliminate current flow through the capillary
• Inactivate the capillary and require replacement

Correct Answer: Create a positively charged surface, reverse or reduce EOF, and reduce adsorption of acidic analytes

Q17. Which of the following is a key advantage of isotachophoresis (ITP) configuration in sample preconcentration?

• ITP separates neutral molecules based solely on size
• ITP can stack and focus ions of similar mobility into highly concentrated zones prior to analysis
• ITP eliminates the need for detectors because zones are visible
• ITP requires no careful choice of leading and trailing electrolytes

Correct Answer: ITP can stack and focus ions of similar mobility into highly concentrated zones prior to analysis

Q18. Which capillary parameter primarily determines the linear velocity and thus influences separation time in a given electric field?

• Capillary wall material (silica vs polymer)
• Capillary total length between inlet and detector
• Capillary outer diameter (o.d.)
• Capillary color

Correct Answer: Capillary total length between inlet and detector

Q19. In MEKC, adding organic modifiers (e.g., methanol) to the buffer typically results in which combined effects?

• Increased micelle size, increased EOF, and no change in selectivity
• Changes in partitioning of analytes into micelles, altered EOF, and modified selectivity and migration times
• Complete precipitation of surfactant and loss of separation
• Elimination of electrophoretic mobility for charged analytes

Correct Answer: Changes in partitioning of analytes into micelles, altered EOF, and modified selectivity and migration times

Q20. Proper capillary preconditioning (rinsing sequence) before an experimental run is necessary primarily to:

• Introduce contaminants that improve peak shape
• Stabilize surface charge, remove adsorbed species, and ensure reproducible EOF and retention behavior
• Increase capillary wall roughness for better separation
• Prevent any current flow through the capillary

Correct Answer: Stabilize surface charge, remove adsorbed species, and ensure reproducible EOF and retention behavior

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