HPLC injectors MCQs With Answer

Introduction: HPLC injectors MCQs With Answer is a focused question set designed for M.Pharm students studying Advanced Instrumental Analysis (MPA 201T). This collection emphasizes the principles, mechanics, and troubleshooting of sample introduction systems in High-Performance Liquid Chromatography (HPLC). Topics covered include manual and autosampler injectors, sample loops, valve positions, dead volume, split/partial/full-loop techniques, carryover, pressure effects, and materials compatibility. Each multiple-choice item probes conceptual understanding and practical problem-solving relevant to laboratory practice and method development. Use these MCQs to assess knowledge, prepare for exams, or review injector-related decisions that influence chromatographic precision, accuracy, and peak integrity.

Q1. Which component determines the fixed sample volume in a full-loop manual injector?

• Injector valve port diameter
• Sample loop length and internal bore
• Syringe stroke volume
• Needle gauge

Correct Answer: Sample loop length and internal bore

Q2. In a split-loop injection mode, what happens to the majority of the sample?

• Entire sample is transferred to the column
• Most sample is discarded through waste and only a fraction enters the column
• Sample is trapped and then released slowly
• Sample evaporates inside the injector loop

Correct Answer: Most sample is discarded through waste and only a fraction enters the column

Q3. What is the primary advantage of a sample loop injector over direct syringe injection for routine HPLC?

• Lower cost of maintenance
• Better defined and reproducible injection volume
• Ability to inject viscous samples without clogging
• No dead volume

Correct Answer: Better defined and reproducible injection volume

Q4. Which injector-related factor most directly increases peak broadening and reduces chromatographic efficiency?

• High mobile phase flow rate
• Excess dead volume between injector and column
• Using acetonitrile as organic modifier
• Short sample loop

Correct Answer: Excess dead volume between injector and column

Q5. Why is stainless steel often used for injector needles and loops in conventional HPLC?

• It has the lowest dead volume of all materials
• It offers chemical resistance, mechanical strength and low compressibility
• It is non-reactive with all sample types including strong acids
• It is the lightest material available

Correct Answer: It offers chemical resistance, mechanical strength and low compressibility

Q6. Which autosampler feature most effectively reduces carryover between injections?

• Slower injection speed
• Use of a pre- and post-injection needle wash with appropriate solvent
• Smaller sample loop
• Higher column temperature

Correct Answer: Use of a pre- and post-injection needle wash with appropriate solvent

Q7. In a 20 µL full-loop injection, which action will directly change the injected volume?

• Changing loop internal bore while maintaining length
• Altering detector wavelength
• Reducing column length
• Changing mobile phase pH

Correct Answer: Changing loop internal bore while maintaining length

Q8. What is the typical cause of air bubble introduction during sample injection using an autosampler?

• Using mobile phase with too high viscosity
• Insufficient purge/degassing of the mobile phase or sample lines
• Excessive column backpressure
• Needle too small in diameter

Correct Answer: Insufficient purge/degassing of the mobile phase or sample lines

Q9. Which injector valve position is correct to fill the sample loop from the sample vial in a typical 6-port loop injector?

• Inject position
• Load (or Fill) position
• Bypass position
• Flush position

Correct Answer: Load (or Fill) position

Q10. How does very high sample viscosity influence injection reproducibility in HPLC?

• Improves reproducibility by damping flow pulses
• Can cause variable displaced volume and slower loop filling leading to poor reproducibility
• Has no effect if the loop size is correct
• Makes peaks narrower due to focused injection

Correct Answer: Can cause variable displaced volume and slower loop filling leading to poor reproducibility

Q11. What is the main function of a needle seat in autosamplers?

• To heat the sample prior to injection
• To create a low dead-volume, leak-free connection between needle and sample loop or column
• To mix sample with mobile phase
• To hold vials in place during injection

Correct Answer: To create a low dead-volume, leak-free connection between needle and sample loop or column

Q12. Which injection technique is recommended when sample solvent strength is much stronger than the initial mobile phase to avoid peak distortion?

• Use full-loop injection without modification
• Use partial-loop injection or perform solvent matching and focalization techniques
• Decrease column temperature drastically
• Always use split-loop mode

Correct Answer: Use partial-loop injection or perform solvent matching and focalization techniques

Q13. What is a primary disadvantage of using very large sample loops for trace analysis?

• Improved sensitivity but increased solvent consumption
• Higher risk of sample dilution, increased dispersion and possible carryover
• Less dead volume
• Shorter equilibration times

Correct Answer: Higher risk of sample dilution, increased dispersion and possible carryover

Q14. Which practice reduces sample compression artifacts when injecting into a high-pressure UHPLC system?

• Use a longer needle
• Use low-compressibility materials (stainless steel) and minimize confined air pockets by proper purging
• Reduce the mobile phase organic content
• Always use split-loop injection

Correct Answer: Use low-compressibility materials (stainless steel) and minimize confined air pockets by proper purging

Q15. If an autosampler shows decreasing injection reproducibility over time, which injector maintenance step is most likely to fix the problem?

• Replace the column
• Clean or replace needle, needle seat and wash ports; re-calibrate injection routine
• Change detector lamp
• Increase mobile phase flow rate

Correct Answer: Clean or replace needle, needle seat and wash ports; re-calibrate injection routine

Q16. What is the expected effect of increasing the injection speed (needle plunger rate) in syringe-type manual injectors?

• No effect on peak shape
• Faster injection can cause pressure surges and peak distortion or variability
• Guaranteed better reproducibility
• Improved resolution due to sharper sample plugs

Correct Answer: Faster injection can cause pressure surges and peak distortion or variability

Q17. Which material is least suitable for injector wetted parts when analyzing strong oxidizing mobile phases?

• PEEK (polyether ether ketone)
• Stainless steel 316
• Titanium
• Glass-lined components

Correct Answer: PEEK (polyether ether ketone)

Q18. What is the impact of injector dead volume located between the injector outlet and the column inlet?

• It improves mixing and peak focusing
• It increases band broadening, reduces efficiency and can shift retention times
• No measurable impact on chromatography
• Decreases system backpressure

Correct Answer: It increases band broadening, reduces efficiency and can shift retention times

Q19. When using an autosampler for carryover-sensitive assays, which strategy provides the most robust reduction of carryover?

• Use the same wash solvent for pre- and post-wash regardless of analyte chemistry
• Implement multi-solvent needle wash including a strong organic and water/acid wash plus air purge
• Only perform post-injection wash
• Increase injection volume to dilute residues

Correct Answer: Implement multi-solvent needle wash including a strong organic and water/acid wash plus air purge

Q20. How is the theoretical loop volume (µL) calculated for an injector sample loop?

• Loop volume = loop length (mm) × internal bore (mm)
• Loop volume = π × (internal radius)^2 × loop length (converted to same units)
• Loop volume = internal bore × pressure drop
• Loop volume = loop length / internal diameter

Correct Answer: Loop volume = π × (internal radius)^2 × loop length (converted to same units)

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