Principle of HPLC MCQs With Answer

Introduction: Principle of HPLC MCQs With Answer is a focused quiz set designed for M.Pharm students studying Advanced Instrumental Analysis (MPA 201T). This collection emphasizes core chromatographic principles—retention mechanisms, column theory, van Deemter behavior, retention factor and selectivity, detectors, interfaces for LC–MS, gradient vs isocratic elution, and method development considerations. Each question probes theoretical understanding and practical implications encountered in pharmaceutical analysis, method optimization and troubleshooting. Answers are provided to reinforce learning and to help students prepare for exams and practicals. Use these MCQs to test comprehension, identify weak areas, and build confidence in applying HPLC principles to real-world analytical problems.

Q1. What is the fundamental principle behind separation in High Performance Liquid Chromatography (HPLC)?

• Differential partitioning between the mobile and stationary phases
• Simple distillation based on boiling points
• Magnetic susceptibility differences between analytes
• Electrophoretic mobility in an electric field

Correct Answer: Differential partitioning between the mobile and stationary phases

Q2. Which description best fits reversed-phase HPLC?

• Nonpolar stationary phase (e.g., C18) and polar mobile phase—hydrophobic retention
• Polar stationary phase and nonpolar mobile phase—hydrophilic retention
• Ionic stationary phase binding charged analytes by exchange
• Stationary phase separates molecules based on size exclusion

Correct Answer: Nonpolar stationary phase (e.g., C18) and polar mobile phase—hydrophobic retention

Q3. The retention factor (k) in HPLC is defined by which expression?

• k = t0 / tR
• k = (tR – t0) / t0
• k = tR × t0
• k = (tR + t0) / 2

Correct Answer: k = (tR – t0) / t0

Q4. Which formula is used to calculate the number of theoretical plates (N) from peak width at baseline?

• N = 5.54 × (tR / w1/2)^2
• N = 16 × (tR / w_b)^2
• N = 2.35 × (tR / w_b)^2
• N = (tR / t0)^2

Correct Answer: N = 16 × (tR / w_b)^2

Q5. In the van Deemter equation, which term describes band broadening due to resistance to mass transfer between mobile and stationary phase?

• A term (eddy diffusion)
• B term (longitudinal diffusion)
• C term (mass transfer resistance)
• None of the above

Correct Answer: C term (mass transfer resistance)

Q6. Selectivity (α) between two solutes in HPLC is defined as:

• The difference in retention times: tR2 – tR1
• The ratio of retention factors: k2 / k1
• The sum of peak widths at baseline
• The square root of the plate number

Correct Answer: The ratio of retention factors: k2 / k1

Q7. Which expression correctly defines chromatographic resolution (Rs) between two adjacent peaks?

• Rs = (tR2 – tR1) / (w1 + w2)
• Rs = 2 × (tR2 – tR1) / (w1 + w2)
• Rs = (tR2 + tR1) / (w1 – w2)
• Rs = (k2 – k1) / α

Correct Answer: Rs = 2 × (tR2 – tR1) / (w1 + w2)

Q8. What is the primary advantage of gradient elution compared to isocratic elution in HPLC?

• It eliminates the need for a detector
• It allows separation of analytes with a wide range of polarities in shorter run times
• It always produces lower backpressure
• It guarantees no peak tailing

Correct Answer: It allows separation of analytes with a wide range of polarities in shorter run times

Q9. When is gradient elution preferred over isocratic elution?

• When all analytes have very similar retention times
• For complex mixtures containing very early and very late eluting compounds
• When using only size-exclusion columns
• Only when operating at extremely low flow rates

Correct Answer: For complex mixtures containing very early and very late eluting compounds

Q10. Which detector is considered relatively universal but is generally incompatible with gradient elution due to baseline instability?

• UV-Vis absorbance detector
• Fluorescence detector
• Refractive index (RI) detector
• PDA (photodiode array) detector

Correct Answer: Refractive index (RI) detector

Q11. For LC–MS coupling of large polar biomolecules (e.g., peptides), which ionization technique is most appropriate?

• Electron impact (EI)
• MALDI
• Electrospray ionization (ESI)
• Fast atom bombardment (FAB)

Correct Answer: Electrospray ionization (ESI)

Q12. Reducing HPLC column particle size (e.g., from 5 μm to 1.7 μm) typically results in:

• Decreased column efficiency and decreased backpressure
• Increased column efficiency and increased backpressure
• No change in efficiency but reduced analysis time only
• Elimination of the need for guard columns

Correct Answer: Increased column efficiency and increased backpressure

Q13. How does mobile phase pH influence HPLC separations of weak acids and bases?

• It has no effect because HPLC is a physical separation only
• It alters the ionization state of analytes, changing retention and selectivity
• It only affects the detector response, not retention
• It only matters for normal-phase columns

Correct Answer: It alters the ionization state of analytes, changing retention and selectivity

Q14. What is the main purpose of using ion-pairing reagents in reversed-phase HPLC?

• To increase volatility for GC coupling
• To form ion pairs with ionic analytes and increase their retention on a nonpolar stationary phase
• To clean the column packing by stripping silanols
• To convert size-exclusion chromatography into reversed-phase chromatography

Correct Answer: To form ion pairs with ionic analytes and increase their retention on a nonpolar stationary phase

Q15. The Height Equivalent to a Theoretical Plate (HETP) is defined as:

• HETP = N / L
• HETP = L / N
• HETP = tR / w
• HETP = (t0 × tR) / N

Correct Answer: HETP = L / N

Q16. In HPLC terminology, the dead time (t0) is best described as:

• The time taken for the most strongly retained analyte to elute
• The time for an unretained solute to pass through the column
• The time between two consecutive injections
• The time for the detector to stabilize after switching on

Correct Answer: The time for an unretained solute to pass through the column

Q17. Peak tailing in reversed-phase HPLC is most commonly caused by:

• Excessive mobile phase flow rate only
• Active silanol sites or secondary interactions on silica-based stationary phases
• Insufficient detector sensitivity
• Using too large an injection loop only

Correct Answer: Active silanol sites or secondary interactions on silica-based stationary phases

Q18. What is a key advantage of a photodiode array (PDA) detector in HPLC?

• It only detects compounds at a single fixed wavelength
• It provides mass spectra for analyte identification
• It records full UV–Vis spectra across multiple wavelengths simultaneously for peak purity assessment
• It is completely unaffected by mobile phase changes

Correct Answer: It records full UV–Vis spectra across multiple wavelengths simultaneously for peak purity assessment

Q19. Which of the following are typical system suitability parameters checked before running analytical HPLC samples?

• Theoretical plates, tailing factor, and resolution
• Carrier gas flow rate and ion source temperature
• pH meter calibration only
• Column length and detector lamp age only

Correct Answer: Theoretical plates, tailing factor, and resolution

Q20. Which HPLC mode is most appropriate for separating very polar, neutral small molecules without chemical derivatization?

• Reversed-phase HPLC
• Normal-phase HPLC
• Size-exclusion chromatography
• Chiral stationary phase

Correct Answer: Normal-phase HPLC

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