Moving boundary electrophoresis MCQs With Answer

Introduction: Moving Boundary Electrophoresis MCQs With Answer

Moving boundary electrophoresis (Tiselius method) is a classical, support-free electrophoretic technique that measures the motion of sharp boundaries formed between sample zones and buffer under an applied electric field. Despite being largely historical in routine practice, it remains foundational for understanding electrophoretic mobility, charge states of biomolecules, and factors like buffer composition, ionic strength, Joule heating, and convection. These MCQs are tailored for M. Pharm students studying Modern Pharmaceutical Analytical Techniques. They probe principles, instrumentation, calculations, method variables, and applications relevant to proteins, peptides, and electrolytes. Each question includes clear answers to help you assess conceptual depth and numerical proficiency essential for advanced pharmaceutical analysis.

Q1. The fundamental principle of moving boundary electrophoresis is to

• Separate analytes based on differential partitioning into a stationary phase
• Detect analytes by their differential solubility in immiscible solvents
• Separate and measure analytes by observing the motion of sharp boundaries in a support-free solution under an electric field
• Resolve analytes through size-dependent sieving in a gel matrix

Correct Answer: Separate and measure analytes by observing the motion of sharp boundaries in a support-free solution under an electric field

Q2. The classical Tiselius moving boundary apparatus is characterized by the use of a

• Planar gel slab with fluorescent imaging
• U-shaped cell with schlieren optics for boundary visualization
• Capillary tube with laser-induced fluorescence detection
• Paper strip with ninhydrin visualization

Correct Answer: U-shaped cell with schlieren optics for boundary visualization

Q3. Electrophoretic mobility (u) in moving boundary electrophoresis is most appropriately expressed as

• u = v × E, with units of V s cm^-2
• u = v/E, with units of cm^2 V^-1 s^-1
• u = E/v, with units of V cm s^-1
• u = L/V, with units of cm V^-1

Correct Answer: u = v/E, with units of cm^2 V^-1 s^-1

Q4. If the boundary displacement is s in time t, the electrode separation is L, and the applied voltage is V, the mobility (u) can be calculated by

• u = (s/t) × (V/L)
• u = (s × L)/(t × V)
• u = (t × V)/(s × L)
• u = (s × V)/(t × L)

Correct Answer: u = (s × L)/(t × V)

Q5. A density gradient (e.g., sucrose) is sometimes added to the solution in moving boundary electrophoresis primarily to

• Increase ionic strength to speed up migration
• Suppress convection and stabilize moving boundaries
• Enhance analyte ionization by lowering pH
• Increase electric field homogeneity by reducing conductivity

Correct Answer: Suppress convection and stabilize moving boundaries

Q6. Endosmotic (electroosmotic) flow at the liquid–glass interface in a Tiselius cell can be minimized by

• Using gelatin-coated glass walls to reduce zeta potential
• Using uncoated glass to increase wall charge
• Operating at extremely low ionic strength
• Increasing temperature to reduce viscosity

Correct Answer: Using gelatin-coated glass walls to reduce zeta potential

Q7. The classical optical method used to visualize moving boundaries in Tiselius electrophoresis is

• Fluorescence microscopy
• Schlieren (refractometric) optics
• Chemiluminescence imaging
• Raman scattering

Correct Answer: Schlieren (refractometric) optics

Q8. In moving boundary experiments, the isoelectric point (pI) of a protein can be estimated by

• Finding the pH at which its mobility becomes zero
• Measuring its maximum absorbance wavelength
• Determining its solubility minimum
• Calculating its diffusion coefficient

Correct Answer: Finding the pH at which its mobility becomes zero

Q9. The Kohlrausch regulating function, as applied to moving boundary electrophoresis, primarily ensures

• That diffusional broadening is eliminated
• Maintenance of constant ionic current across the boundary, supporting sharp, steady boundary motion
• That electrolysis at electrodes does not occur
• Uniform temperature across the cell without cooling

Correct Answer: Maintenance of constant ionic current across the boundary, supporting sharp, steady boundary motion

Q10. The cooling jacket in a Tiselius cell is essential mainly to

• Increase ionization of weak electrolytes
• Reduce Joule heating, preventing thermal convection and boundary distortion
• Increase electric field strength
• Enhance optical resolution of the detector

Correct Answer: Reduce Joule heating, preventing thermal convection and boundary distortion

Q11. A key limitation of moving boundary electrophoresis for routine analytical work is

• Requirement of large sample volumes and relatively low resolution
• Inability to analyze proteins
• Incompatibility with aqueous buffers
• Excessively high cost of buffers

Correct Answer: Requirement of large sample volumes and relatively low resolution

Q12. Increasing buffer ionic strength in moving boundary electrophoresis generally

• Increases observed electrophoretic mobility
• Decreases observed electrophoretic mobility and increases Joule heating
• Eliminates electroosmosis completely
• Has no effect on boundary sharpness

Correct Answer: Decreases observed electrophoretic mobility and increases Joule heating

Q13. For a protein whose pI is 6.8, at pH 8.0 in moving boundary electrophoresis, it will

• Be positively charged and move toward the cathode
• Be negatively charged and move toward the anode
• Have zero net charge and not move
• Precipitate at the boundary

Correct Answer: Be negatively charged and move toward the anode

Q14. Diffusional spreading of boundaries can be reduced by

• Adding sucrose or glycerol to increase viscosity and operating at lower temperature
• Using very low viscosity solvents at high temperature
• Removing the cooling jacket
• Using pure water without buffer

Correct Answer: Adding sucrose or glycerol to increase viscosity and operating at lower temperature

Q15. A boundary moves 0.50 cm in 120 s with an applied voltage of 200 V across 20 cm. The electrophoretic mobility is

• 4.17 × 10^-4 cm^2 V^-1 s^-1
• 4.17 × 10^-5 cm^2 V^-1 s^-1
• 2.50 × 10^-3 cm^2 V^-1 s^-1
• 1.00 × 10^-4 cm^2 V^-1 s^-1

Correct Answer: 4.17 × 10^-4 cm^2 V^-1 s^-1

Q16. If a protein has u = 3.0 × 10^-4 cm^2 V^-1 s^-1 and the field strength is 8 V cm^-1, how long will it take the boundary to move 0.72 cm?

• 150 s
• 300 s (5 min)
• 600 s (10 min)
• 120 s (2 min)

Correct Answer: 300 s (5 min)

Q17. For non-UV-absorbing solutes, boundary detection in the Tiselius method is best achieved by

• Schlieren refractometric optics sensitive to refractive index gradients
• Electrochemical amperometry
• Fluorescence quenching
• Radioactivity counting

Correct Answer: Schlieren refractometric optics sensitive to refractive index gradients

Q18. A seminal application of Tiselius moving boundary electrophoresis was the separation and characterization of

• DNA restriction fragments by size
• Serum proteins into albumin and alpha-, beta-, gamma-globulins
• Small organic acids by volatility
• Lipids by hydrophobicity

Correct Answer: Serum proteins into albumin and alpha-, beta-, gamma-globulins

Q19. To minimize pH shifts due to electrolysis at the electrodes during a run, the Tiselius setup commonly employs

• Platinum electrodes immersed directly in the analytical column without buffers
• Large buffer reservoirs with salt bridges and reversible electrodes (e.g., Ag/AgCl)
• Dry electrodes to avoid gas formation
• Organic solvents to suppress ionization

Correct Answer: Large buffer reservoirs with salt bridges and reversible electrodes (e.g., Ag/AgCl)

Q20. Compared with zone electrophoresis in gels, moving boundary electrophoresis typically

• Offers higher resolution and smaller sample requirements
• Is support-free, gives lower resolution, and requires larger sample volumes
• Uses immobilized pH gradients for focusing
• Relies exclusively on fluorescence for detection

Correct Answer: Is support-free, gives lower resolution, and requires larger sample volumes

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