Band broadening and its causes MCQs With Answer

Introduction: This set of MCQs on Band broadening and its causes is designed specifically for M.Pharm students studying Advanced Instrumental Analysis (MPA 201T). It reviews key theoretical concepts—such as the van Deemter equation, longitudinal diffusion, eddy diffusion, and mass-transfer resistance—along with practical contributors to peak spreading like column packing, particle size, extra‑column effects, injection and detector volumes, and solvent/matrix mismatches. The questions range from foundational definitions to applied problem‑solving relevant to HPLC and GC, helping students strengthen conceptual understanding and prepare for exams and laboratory troubleshooting. Use these items to test, revise, and deepen your mastery of chromatographic band broadening.

Q1. Which of the following expressions correctly represents the van Deemter equation for plate height H as a function of linear velocity u?

• H = A + B·u + C/u
• H = A + (B/u) + C·u
• H = A·u + B + C/u
• H = A/u + B·u + C

Correct Answer: H = A + (B/u) + C·u

Q2. In the van Deemter equation, the A term primarily describes which cause of band broadening?

• Longitudinal diffusion along the column
• Eddy diffusion due to multiple flow paths in packed beds
• Mass transfer resistance between phases
• Detector response time

Correct Answer: Eddy diffusion due to multiple flow paths in packed beds

Q3. Which factor mainly contributes to the B term (B/u) in the van Deemter equation?

• Finite time required for solute exchange between mobile and stationary phases
• Multiple flow paths within the packed column
• Longitudinal (axial) diffusion of analyte in the mobile phase
• Extra‑column volume (tubing and detector cell)

Correct Answer: Longitudinal (axial) diffusion of analyte in the mobile phase

Q4. The C term in the van Deemter equation is associated with:

• Instrument electronic noise
• Band broadening due to finite mass transfer kinetics between mobile and stationary phases
• Pressure fluctuations in the pump
• Adsorption equilibrium constant only

Correct Answer: Band broadening due to finite mass transfer kinetics between mobile and stationary phases

Q5. How does decreasing particle diameter of a packed stationary phase generally affect column efficiency?

• Decreases efficiency by increasing the A term
• Has no effect on plate height
• Improves efficiency by reducing both A and C contributions to H
• Improves efficiency but increases longitudinal diffusion dramatically

Correct Answer: Improves efficiency by reducing both A and C contributions to H

Q6. Which of the following is a primary source of extra‑column band broadening in HPLC?

• Mobile phase composition
• Detector cell volume and connecting tubing
• Stationary phase pore size
• Column oven temperature control

Correct Answer: Detector cell volume and connecting tubing

Q7. For a given column, the optimum linear velocity (u_opt) that minimizes plate height can be estimated from the van Deemter parameters as:

• u_opt = B/C
• u_opt = sqrt(B·C)
• u_opt = sqrt(B/C)
• u_opt = B + C

Correct Answer: u_opt = sqrt(B/C)

Q8. Which statement best explains why longitudinal diffusion is more problematic in GC than in liquid chromatography?

• Diffusion coefficients in gases are much larger than in liquids, increasing axial spreading at low flow rates
• Gas chromatography uses lower temperatures which increase diffusion
• Detectors in GC always broaden peaks more than LC detectors
• Packed columns are not used in GC so eddy diffusion dominates

Correct Answer: Diffusion coefficients in gases are much larger than in liquids, increasing axial spreading at low flow rates

Q9. Which change will generally reduce mass‑transfer related band broadening (C term) in a packed HPLC column?

• Increase particle diameter
• Increase mobile phase viscosity
• Use smaller particles and reduce stationary phase film thickness
• Lower column temperature drastically

Correct Answer: Use smaller particles and reduce stationary phase film thickness

Q10. Taylor‑Aris dispersion describes band broadening caused by:

• Radial concentration gradients in laminar flow within an open tubular column leading to enhanced axial dispersion
• Non‑ideal injection volumes only
• Irreversible adsorption on stationary phase
• Electronic filtering in detector circuits

Correct Answer: Radial concentration gradients in laminar flow within an open tubular column leading to enhanced axial dispersion

Q11. A very large injection volume relative to column dimensions will typically cause:

• Reduced retention times but unchanged peak shapes
• Band broadening and fronting or tailing depending on solvent strength
• Only symmetric peak sharpening
• No effect if the detector is fast

Correct Answer: Band broadening and fronting or tailing depending on solvent strength

Q12. Slow adsorption–desorption kinetics between mobile and stationary phases will primarily affect which term in band broadening?

• B term (longitudinal diffusion)
• A term (eddy diffusion)
• C term (mass transfer kinetics)
• Extra‑column term only

Correct Answer: C term (mass transfer kinetics)

Q13. Which experimental adjustment is most effective to reduce eddy diffusion in packed columns?

• Use a column packed with more uniformly sized particles and better packing quality
• Switch to a detector with a larger cell volume
• Increase injection volume
• Lower the mobile phase flow rate to near zero

Correct Answer: Use a column packed with more uniformly sized particles and better packing quality

Q14. How does increasing mobile phase flow rate typically affect peak width in HPLC?

• Always increases peak width because longitudinal diffusion increases at high flow
• Decreases contribution from longitudinal diffusion but increases mass transfer broadening, producing a minimum at an optimum flow
• Has no effect on peak width
• Always decreases peak width linearly

Correct Answer: Decreases contribution from longitudinal diffusion but increases mass transfer broadening, producing a minimum at an optimum flow

Q15. Which of the following describes a common effect of solvent strength mismatch between sample solvent and mobile phase on peak shape?

• It only affects retention time but not peak width
• It can cause peak distortion such as fronting when the injection solvent is stronger than the mobile phase
• It reduces eddy diffusion in the column
• It increases the diffusion coefficient of solute molecules

Correct Answer: It can cause peak distortion such as fronting when the injection solvent is stronger than the mobile phase

Q16. Which parameter combines column length and plate height to give the number of theoretical plates (N)?

• N = H/L
• N = L/H
• N = H·L
• N = sqrt(L·H)

Correct Answer: N = L/H

Q17. Extra‑column effects become proportionally more important when:

• Analyzing large molecules only
• Using very short or very high‑efficiency columns where column contribution to variance is small
• Column diameter is increased to very large bore only
• Flow rate is set to zero

Correct Answer: Using very short or very high‑efficiency columns where column contribution to variance is small

Q18. Which of the following best explains why high temperatures can improve separation efficiency in liquid chromatography?

• Temperature increases stationary phase particle size
• Higher temperature reduces mobile phase viscosity and increases diffusion coefficients, lowering mass transfer resistance
• Temperature alters detector sensitivity only
• Higher temperature eliminates eddy diffusion entirely

Correct Answer: Higher temperature reduces mobile phase viscosity and increases diffusion coefficients, lowering mass transfer resistance

Q19. In capillary electrochromatography or capillary LC, which phenomenon can dominate band broadening at long analysis times?

• Detector electronics noise
• Taylor dispersion from parabolic flow profile and axial diffusion
• Excessive eddy diffusion from packed beds only
• Stationary phase chemical decomposition

Correct Answer: Taylor dispersion from parabolic flow profile and axial diffusion

Q20. When troubleshooting unexpectedly broad peaks in HPLC, which sequence of checks is most appropriate?

• Check column age/packing, then extra‑column tubing and detector cell, then injection volume and solvent match
• Replace detector first, then change mobile phase, then ignore column
• Increase temperature immediately, then increase injection volume
• Only reduce flow rate and assume the problem is solved

Correct Answer: Check column age/packing, then extra‑column tubing and detector cell, then injection volume and solvent match

Download