Peak shapes and chromatographic behavior MCQs With Answer

Introduction: Peak shapes and chromatographic behavior are central to interpreting and optimizing separation methods in M.Pharm studies. This blog presents targeted MCQs designed to deepen your understanding of why peaks deviate from ideal shapes, how instrumental and physicochemical factors influence band broadening, and strategies to improve chromatographic efficiency. Questions cover concepts such as Gaussian peaks, tailing and fronting mechanisms, Van Deemter contributions, extra-column effects, overloading, pH and temperature impacts, and practical remedies like stationary phase selection and mobile phase modifiers. These MCQs are crafted to reinforce advanced instrumental analysis concepts and to prepare you for real-world method development and troubleshooting in pharmaceutical chromatography.

Q1. Which description best defines an ideal Gaussian peak in chromatography?

• A perfectly symmetrical bell-shaped peak resulting from random diffusion and ideal mass transfer
• A peak with pronounced tailing due to irreversible adsorption
• A fronting peak caused by column overload
• An asymmetrical peak produced by instrumentation lag

Correct Answer: A perfectly symmetrical bell-shaped peak resulting from random diffusion and ideal mass transfer

Q2. A peak tailing where the trailing edge is extended is most commonly caused by which phenomenon?

• Saturation of stationary phase leading to fronting
• Secondary interactions with active sites on the stationary phase (e.g., silanols)
• Excessively small particle size
• High column temperature improving mass transfer

Correct Answer: Secondary interactions with active sites on the stationary phase (e.g., silanols)

Q3. Peak fronting in chromatography typically indicates which of the following?

• Insufficient column packing uniformity (eddy diffusion)
• Overloading of the stationary phase capacity causing nonlinear isotherm effects
• Excessive detector response time
• Intrinsic longitudinal diffusion at high flow rates

Correct Answer: Overloading of the stationary phase capacity causing nonlinear isotherm effects

Q4. Which statement correctly distinguishes the asymmetry factor (As) and the USP tailing factor (T)?

• As is defined as b/a at 10% peak height while the USP tailing factor is measured at 5% peak height
• As is measured at 5% peak height; USP tailing factor uses 10% peak height
• Both As and T are always numerically identical for any peak
• As is independent of peak height while T is based on baseline width only

Correct Answer: As is defined as b/a at 10% peak height while the USP tailing factor is measured at 5% peak height

Q5. In the Van Deemter equation (H = A + B/u + C·u), which term mainly increases with increasing linear velocity and represents resistance to mass transfer?

• The A term (eddy diffusion)
• The B term (longitudinal diffusion)
• The C term (mass transfer resistance)
• The A and B terms equally

Correct Answer: The C term (mass transfer resistance)

Q6. Which of the following is least likely to contribute to chromatographic band broadening?

• Extra-column dead volume such as long tubing and large injection loops
• Detector cell volume and response time
• Significantly decreasing particle size of the stationary phase
• Poor injector mixing and dispersion

Correct Answer: Significantly decreasing particle size of the stationary phase

Q7. Which equation correctly relates theoretical plates (N) to retention time (tr) and peak width at half height (w1/2) for a Gaussian peak?

• N = 5.54 × (tr / w1/2)^2
• N = (tr / w1/2)
• N = 16 × (tr / w1/2)^2
• N = tr × w1/2

Correct Answer: N = 5.54 × (tr / w1/2)^2

Q8. For modern UHPLC with very narrow-bore columns, which extra-column source most commonly dominates and degrades peak shape?

• Stationary phase pore size
• Connecting tubing dead volume and injector dispersion
• Mobile phase composition variability
• Detector wavelength selection

Correct Answer: Connecting tubing dead volume and injector dispersion

Q9. Overloading a column with a large sample mass most often causes which observable change in peak shape?

• Sharper, narrower peaks with shorter retention
• Peak fronting due to saturation of binding sites and nonlinear isotherms
• No change if injection solvent is identical to mobile phase
• Only an increase in detector baseline noise

Correct Answer: Peak fronting due to saturation of binding sites and nonlinear isotherms

Q10. Slow equilibration kinetics between mobile and stationary phases will most likely produce which chromatographic artifact?

• Reduced column bleed but unchanged peak shape
• Peak tailing due to incomplete mass transfer during transit
• Peak fronting caused by fast adsorption/desorption
• A purely Gaussian peak with increased height

Correct Answer: Peak tailing due to incomplete mass transfer during transit

Q11. Basic analytes frequently show peak tailing on silica-based reversed-phase columns primarily because of:

• Excessively low column temperature
• Residual silanol groups causing secondary ionic interactions
• High mobile phase organic content
• Use of end-capped stationary phases

Correct Answer: Residual silanol groups causing secondary ionic interactions

Q12. How does mobile phase pH near the pKa of an ionizable analyte commonly affect peak shape?

• It usually sharpens peaks by ensuring single ionic form
• It causes peak broadening or asymmetry due to mixed ionization states and variable retention
• It has no effect on retention or shape
• It always eliminates secondary interactions with stationary phase

Correct Answer: It causes peak broadening or asymmetry due to mixed ionization states and variable retention

Q13. Which mobile phase additive is commonly used to reduce tailing of basic compounds by masking residual silanols?

• Strong acids like trifluoroacetic acid in high concentration
• Amine modifiers such as triethylamine at low concentration
• Chelating agents like EDTA
• Aliphatic hydrocarbons

Correct Answer: Amine modifiers such as triethylamine at low concentration

Q14. Increasing the column temperature typically has which combined effect on chromatographic peaks for many solutes?

• Increases retention time and broadens peaks
• Decreases retention time, lowers viscosity, and often sharpens peaks by improving mass transfer
• Has no effect on retention or peak width
• Always causes peak fronting regardless of analyte chemistry

Correct Answer: Decreases retention time, lowers viscosity, and often sharpens peaks by improving mass transfer

Q15. A sudden observation of very broad peaks after method transfer is most likely caused by which issue?

• Too small detector cell volume on the new system
• Excessively large injection volume relative to column capacity on the receiving system
• Use of a higher column temperature
• Improved column packing on the new instrument

Correct Answer: Excessively large injection volume relative to column capacity on the receiving system

Q16. Longitudinal diffusion contributes most to band broadening under which chromatographic condition?

• At very high linear velocities
• At very low linear velocities (slow mobile phase flow)
• Only when particle size is extremely small
• Only in gas chromatography, not in liquid chromatography

Correct Answer: At very low linear velocities (slow mobile phase flow)

Q17. Which detector characteristic most directly increases observed peak width due to extra-column effects?

• Detector wavelength accuracy
• Large detector cell volume causing dispersion inside the cell
• High detector sensitivity
• Short detector response time

Correct Answer: Large detector cell volume causing dispersion inside the cell

Q18. How does decreasing stationary phase particle size generally affect column efficiency (N) and plate height (H)?

• Decreasing particle size increases plate height and decreases efficiency
• Decreasing particle size reduces plate height and increases theoretical plates (efficiency)
• Particle size has no effect on H or N
• Smaller particles always worsen peak symmetry

Correct Answer: Decreasing particle size reduces plate height and increases theoretical plates (efficiency)

Q19. What asymmetry factor (As) value corresponds to a perfectly symmetric chromatographic peak?

• 0
• 1
• 2
• Greater than 5

Correct Answer: 1

Q20. Which combined approach is most effective for reducing tailing of basic analytes in reversed-phase LC?

• Use a nonpolar stationary phase and remove buffer from mobile phase entirely
• Switch to a smaller particle size without changing chemistry
• Use an end-capped or specially deactivated stationary phase and add a low concentration amine modifier (e.g., triethylamine) to the mobile phase
• Increase injection volume and lower column temperature

Correct Answer: Use an end-capped or specially deactivated stationary phase and add a low concentration amine modifier (e.g., triethylamine) to the mobile phase

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