CE-MS hyphenation MCQs With Answer

This blog presents a focused set of CE–MS hyphenation multiple-choice questions tailored for M.Pharm students studying Advanced Instrumental Analysis (MPA 201T). The questions emphasize practical and theoretical aspects of coupling capillary electrophoresis (CE) with mass spectrometry (MS), including interface types (sheath-flow, sheathless, porous-tip), electrospray considerations, buffer selection, sample stacking, and strategies to improve sensitivity and reproducibility. Each item is designed to test understanding of separation physics, ionization compatibility, and common troubleshooting in CE–MS workflows. Use these MCQs for revision, classroom quizzes, or self-assessment to strengthen your ability to design and interpret CE–MS experiments relevant to pharmaceutical analysis.

Q1. What is the primary technical challenge when coupling capillary electrophoresis (CE) to mass spectrometry (MS)?

• Aligning CE capillary dimensions with MS inlet diameter
• Maintaining electrospray stability while electrically decoupling CE current from the MS
• Reducing capillary temperature to prevent analyte degradation
• Achieving universal ionization for both polar and nonpolar analytes

Correct Answer: Maintaining electrospray stability while electrically decoupling CE current from the MS

Q2. Which ionization technique is most commonly used in CE–MS hyphenation for small molecules and peptides?

• Atmospheric pressure chemical ionization (APCI)
• Matrix-assisted laser desorption ionization (MALDI)
• Electrospray ionization (ESI)
• Electron ionization (EI)

Correct Answer: Electrospray ionization (ESI)

Q3. Which type of CE–MS interface uses a conductive sheath liquid that surrounds the capillary tip and provides electrical contact for ESI?

• Sheathless porous-tip interface
• Sheath-flow (coaxial) interface
• Direct liquid junction interface
• Off-line fraction collection interface

Correct Answer: Sheath-flow (coaxial) interface

Q4. What is the main advantage of a sheathless CE–MS interface compared to a sheath-flow interface?

• Better compatibility with nonvolatile buffers
• Higher sample throughput due to faster injections
• Improved sensitivity because there is minimal dilution of the CE effluent
• Simpler electrical grounding without modifications

Correct Answer: Improved sensitivity because there is minimal dilution of the CE effluent

Q5. Typical CE flow rates that are compatible with nano-ESI in CE–MS are in which range?

• mL per minute
• 100s μL per minute
• nL to low μL per minute (suitable for nano-ESI)
• No flow, only pressure-driven bursts

Correct Answer: nL to low μL per minute (suitable for nano-ESI)

Q6. What is the primary role of the background electrolyte (BGE) in CE when coupled to MS?

• To serve as the electrospray sheath liquid exclusively
• To provide ionic strength and establish the electroosmotic flow and current for separation
• To chemically derivatize analytes for better ionization
• To increase capillary wall conductivity for heating control

Correct Answer: To provide ionic strength and establish the electroosmotic flow and current for separation

Q7. How can electroosmotic flow (EOF) in silica capillaries be reduced to improve separation of cationic pharmaceuticals?

• Increase buffer pH to strongly basic conditions
• Use highly concentrated inorganic salts in the BGE
• Lower the pH (use acidic buffer) or use dynamic/static capillary coatings
• Apply pulsed high-voltage instead of constant voltage

Correct Answer: Lower the pH (use acidic buffer) or use dynamic/static capillary coatings

Q8. Which on-line preconcentration method is most often used in CE–MS to increase sensitivity for trace analytes?

• Solid-phase extraction after CE separation
• Field-amplified sample stacking (FASS)
• Increasing capillary inner diameter to load more sample
• Heating the capillary to reduce viscosity

Correct Answer: Field-amplified sample stacking (FASS)

Q9. Why is an organic solvent (e.g., methanol or acetonitrile) commonly added to the sheath liquid in a sheath-flow CE–MS interface?

• To neutralize analyte charge and prevent migration
• To improve electrospray desolvation and spray stability
• To increase the buffer ionic strength for CE separation
• To polymerize the capillary tip for better mechanical strength

Correct Answer: To improve electrospray desolvation and spray stability

Q10. Which type of mass analyzer is frequently paired with CE–MS when high mass accuracy and fast acquisition are required for metabolomics?

• Magnetic sector
• Time-of-flight (TOF)
• Ion trap with low resolution
• Flame ionization detector (FID)

Correct Answer: Time-of-flight (TOF)

Q11. How does high conductivity of the BGE affect CE–ESI-MS performance?

• It has no effect on electrospray or separation
• It improves electrospray efficiency by increasing current
• It can destabilize electrospray and increase current, requiring optimization
• It selectively enhances formation of negative ions only

Correct Answer: It can destabilize electrospray and increase current, requiring optimization

Q12. In a sheath-flow interface, what is a key function of the sheath liquid besides acting as solvent for ESI?

• To eliminate the necessity of a background electrolyte
• To provide an electrical contact (ground/reference) and often cause dilution
• To coat the capillary inner wall for reduced adsorption
• To chemically derivatize analytes to improve separation

Correct Answer: To provide an electrical contact (ground/reference) and often cause dilution

Q13. What is electrokinetic injection in CE sample introduction?

• Pressure-driven injection of a fixed-volume plug
• Injection by applying an electric field so charged species migrate into the capillary
• Manual pipetting of sample into the capillary inlet
• Immobilization of sample onto a solid phase inside the capillary

Correct Answer: Injection by applying an electric field so charged species migrate into the capillary

Q14. Which statement correctly describes a porous-tip sheathless interface?

• It uses a large outer capillary to enclose the inner capillary for increased dilution
• The capillary tip is made porous to allow electrical contact while minimizing effluent dilution, improving sensitivity
• It requires nonvolatile salts to maintain conductivity
• It is incompatible with peptide and protein analysis

Correct Answer: The capillary tip is made porous to allow electrical contact while minimizing effluent dilution, improving sensitivity

Q15. Why are volatile buffers (e.g., ammonium acetate, formate) preferred in CE–MS?

• They increase EOF dramatically for faster separations
• They are cheaper than nonvolatile salts
• They evaporate in the ESI process and reduce salt deposition and ion suppression in the MS
• They produce stronger UV absorbance for simultaneous detection

Correct Answer: They evaporate in the ESI process and reduce salt deposition and ion suppression in the MS

Q16. Which CE mode allows separation of neutral compounds and is frequently used in CE–MS for drug impurities?

• Capillary zone electrophoresis (CZE)
• Micellar electrokinetic chromatography (MEKC)
• Isoelectric focusing (IEF)
• Capillary gel electrophoresis (CGE)

Correct Answer: Micellar electrokinetic chromatography (MEKC)

Q17. What is the main effect of using a high sheath flow rate in a sheath-flow CE–MS interface?

• Improved mass resolution in the mass spectrometer
• Increased dilution of analyte leading to decreased sensitivity
• Suppression of electroosmotic flow inside the capillary
• Complete elimination of background ions

Correct Answer: Increased dilution of analyte leading to decreased sensitivity

Q18. Which of the following strategies will most effectively improve sensitivity in CE–MS for low-abundance pharmaceuticals?

• Use a larger inner diameter capillary without changing other conditions
• Employ sheathless interface and on-line preconcentration techniques such as stacking
• Replace ESI with atmospheric pressure chemical ionization (APCI)
• Increase buffer ionic strength drastically

Correct Answer: Employ sheathless interface and on-line preconcentration techniques such as stacking

Q19. In CE–MS, what does electrical decoupling (or grounding/decoupler) refer to?

• Separating the capillary physically from the MS inlet to avoid contamination
• Separating or managing the CE separation voltage/current from the MS high-voltage electrospray to prevent interference
• Disconnecting the mass spectrometer electronics during CE runs
• Using AC instead of DC voltage for CE separations

Correct Answer: Separating or managing the CE separation voltage/current from the MS high-voltage electrospray to prevent interference

Q20. Which practice helps reduce protein adsorption to silica capillary walls and improves reproducibility of protein CE–MS separations?

• Use of uncoated bare fused-silica capillaries with high ionic strength
• Applying dynamic or covalent capillary coatings (e.g., polyacrylamide) and using appropriate BGE additives
• Raising the buffer temperature above 80 °C during separation
• Replacing the capillary after every single injection

Correct Answer: Applying dynamic or covalent capillary coatings (e.g., polyacrylamide) and using appropriate BGE additives

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