Instrumentation of electrophoresis systems MCQs With Answer

Instrumentation of electrophoresis systems MCQs With Answer

Electrophoresis is a cornerstone technique in Modern Pharmaceutical Analytical Techniques, enabling precise separation and characterization of biomolecules and small-molecule drugs. For M. Pharm students, mastering the instrumentation behind slab gel and capillary platforms is crucial for robust method development, data quality, and regulatory-ready results. This quiz focuses on practical aspects of electrophoresis instrumentation: high-voltage power supplies, electrodes, buffer reservoirs, temperature control, capillary materials and coatings, sample injection strategies, and detectors (UV, LIF, conductivity, MS). You will also encounter questions on safety interlocks, cooling systems, imaging modules, and CE modes such as CZE, MEKC, CGE, and cIEF. Use these MCQs to sharpen your understanding of how design choices impact resolution, sensitivity, reproducibility, and throughput.

Q1. What is the primary requirement of the high-voltage power supply used in electrophoresis systems?

• Provide high-voltage AC with adjustable frequency
• Provide stabilized high-voltage DC with low ripple and programmable constant voltage/current/power modes
• Provide pulsed DC with high ripple for enhanced mobility
• Provide low-voltage DC to minimize Joule heating

Correct Answer: Provide stabilized high-voltage DC with low ripple and programmable constant voltage/current/power modes

Q2. Typical operating voltage range for analytical capillary electrophoresis (CE) instruments is:

• 0.1–1 kV
• 3–7 kV
• 10–30 kV
• 60–100 kV

Correct Answer: 10–30 kV

Q3. Which electrode material is most commonly used in electrophoresis tanks and CE buffer reservoirs due to its inertness?

• Copper
• Platinum
• Aluminum
• Graphite

Correct Answer: Platinum

Q4. The primary function of buffer reservoirs in electrophoresis instrumentation is to:

• Increase the viscosity of the separation medium
• Provide ionic continuity between electrodes and the separation medium while maintaining buffer composition
• Reduce detector noise by grounding the system
• Generate the pH gradient for all separations

Correct Answer: Provide ionic continuity between electrodes and the separation medium while maintaining buffer composition

Q5. Temperature control (e.g., air, liquid, or Peltier cooling) is critical in CE primarily to:

• Increase electroosmotic flow by warming the buffer
• Dissipate Joule heat and stabilize viscosity/EOF, improving efficiency and migration time reproducibility
• Reduce detector baseline by cooling the photodiode
• Allow use of non-volatile buffers at high concentration

Correct Answer: Dissipate Joule heat and stabilize viscosity/EOF, improving efficiency and migration time reproducibility

Q6. Which detector offers the highest sensitivity for appropriately labeled analytes in capillary electrophoresis?

• On-capillary UV absorbance (fixed wavelength)
• Laser-induced fluorescence (LIF)
• Contactless conductivity
• Electrochemical amperometric

Correct Answer: Laser-induced fluorescence (LIF)

Q7. Compared to electrokinetic injection, hydrodynamic injection in CE is preferred when the goal is to:

• Favor injection of higher mobility ions
• Minimize bias from analyte mobility and sample matrix conductivity differences
• Increase electrical load on the power supply
• Eliminate the need for pressure control

Correct Answer: Minimize bias from analyte mobility and sample matrix conductivity differences

Q8. In on-capillary UV detection for CE, the optical detection window is created by:

• Drilling a hole through the capillary wall
• Embedding a quartz window during capillary manufacture
• Burning/stripping the polyimide coating to expose a transparent section of fused silica
• Attaching an external lens to the capillary

Correct Answer: Burning/stripping the polyimide coating to expose a transparent section of fused silica

Q9. To suppress electroosmotic flow and reduce protein adsorption in CE, a common strategy is to use:

• Higher ionic strength without any coating
• Dynamic neutral polymer coating of the capillary wall (e.g., PVP)
• Chemical etching to roughen the inner wall
• Thicker polyimide outer coating

Correct Answer: Dynamic neutral polymer coating of the capillary wall (e.g., PVP)

Q10. Why do vertical slab gel electrophoresis units employ separate upper and lower buffer chambers divided by the gel?

• To allow alternating current to circulate
• To establish a discontinuous buffer system and force current through the gel for stacking and resolving
• To prevent oxygen diffusion into the gel
• To increase the path length for UV detection

Correct Answer: To establish a discontinuous buffer system and force current through the gel for stacking and resolving

Q11. For nucleic acid gels stained with ethidium bromide, an appropriate imaging module in the instrumentation is:

• Blue LED array without emission filters
• UV transilluminator (≈302–312 nm) with emission filter and a camera
• White light epi-illumination only
• Infrared laser scanner

Correct Answer: UV transilluminator (≈302–312 nm) with emission filter and a camera

Q12. “Smiling” of bands in slab gel electrophoresis is best minimized by instrumentation that provides:

• Higher gel percentage
• Uniform and efficient cooling via a heat sink or recirculating chiller
• Longer separation distance only
• Low-conductivity buffers without cooling

Correct Answer: Uniform and efficient cooling via a heat sink or recirculating chiller

Q13. A typical pre-run conditioning sequence for a bare fused-silica capillary in CZE is:

• Water → buffer → organic solvent
• 0.1 M NaOH → water → run buffer
• Acetone → methanol → water
• Run buffer only

Correct Answer: 0.1 M NaOH → water → run buffer

Q14. Common inner diameter range used for analytical CE capillaries to balance efficiency and current is:

• 5–10 μm
• 25–75 μm
• 200–500 μm
• 1–2 mm

Correct Answer: 25–75 μm

Q15. Which CE mode requires the addition of surfactant micelles to the running buffer to enable separation of neutral analytes?

• CZE (Capillary Zone Electrophoresis)
• MEKC (Micellar Electrokinetic Chromatography)
• CIEF (Capillary Isoelectric Focusing)
• CGE (Capillary Gel Electrophoresis)

Correct Answer: MEKC (Micellar Electrokinetic Chromatography)

Q16. In CE–MS hyphenation, a commonly used interface that provides electrical contact and stabilizes electrospray is the:

• Direct infusion without any sheath
• Sheath-flow electrospray interface
• Thermal nebulizer interface
• UV photolysis interface

Correct Answer: Sheath-flow electrospray interface

Q17. For slab gel electrophoresis, which power supply control mode best maintains a consistent electric field across the gel during a run?

• Constant current
• Constant power
• Constant voltage
• Pulsed voltage

Correct Answer: Constant voltage

Q18. Contactless conductivity detection (C4D) in CE typically employs:

• Electrodes embedded inside the capillary lumen
• External AC-driven electrodes capacitively coupled through the capillary wall
• DC electrodes at the capillary outlet only
• Laser excitation and photomultiplier detection

Correct Answer: External AC-driven electrodes capacitively coupled through the capillary wall

Q19. In bare fused-silica capillaries, which parameter most directly governs the magnitude of electroosmotic flow (EOF)?

• Detector slit width
• Buffer pH (via surface charge and zeta potential)
• Capillary outer diameter
• Voltage ripple of the power supply

Correct Answer: Buffer pH (via surface charge and zeta potential)

Q20. During isoelectric focusing (e.g., with IPG strips), an appropriate power program to protect the device and ensure focusing is:

• Immediate application of maximum voltage without limits
• Programmed voltage ramp to high kV with current/power limits and active temperature control
• Constant current at room temperature without monitoring
• Alternating polarity to sharpen bands

Correct Answer: Programmed voltage ramp to high kV with current/power limits and active temperature control

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