Column problems and troubleshooting MCQs With Answer

Introduction: Column problems and troubleshooting are central skills for any M.Pharm student working with chromatographic techniques such as HPLC and GC. This blog focuses on common column-related issues — for example, increased backpressure, peak tailing, fronting, loss of resolution, ghost peaks, and column bleed — and practical troubleshooting strategies. You will learn to diagnose causes like particle packing degradation, contamination, incompatible mobile phase pH, sample overload, dead volume, or improper storage, and apply corrective actions such as column flushing, regeneration, guard column use, and optimized operating conditions. These targeted MCQs will reinforce theoretical understanding and develop decision-making skills for real laboratory situations.

Q1. What is the most likely cause of a sudden, significant increase in HPLC backpressure?

• Degradation of stationary phase due to high temperature
• Blockage at the column inlet from particulate matter
• Mobile phase composition change to more polar solvent
• Detector lamp ageing

Correct Answer: Blockage at the column inlet from particulate matter

Q2. Persistent peak tailing for basic analytes in reversed-phase HPLC is commonly caused by:

• Use of mobile phase pH below the column’s pH limit
• Interaction of basic analytes with free silanols on silica-based stationary phases
• Excessive column temperature
• Injection volume too low

Correct Answer: Interaction of basic analytes with free silanols on silica-based stationary phases

Q3. Which troubleshooting step is most appropriate when you observe broad and poorly resolved peaks but normal backpressure?

• Replace the detector cell
• Check and reduce system dead volume (tubing, fittings)
• Increase column temperature beyond recommended limit
• Switch to a higher flow rate immediately

Correct Answer: Check and reduce system dead volume (tubing, fittings)

Q4. Column fronting (peaks skewed to the front) is often caused by:

• Strong secondary interactions with stationary phase
• Sample overload relative to column capacity
• Mobile phase pH being within recommended range
• Use of guard column

Correct Answer: Sample overload relative to column capacity

Q5. A gradual increase in baseline noise and elevated detector signal when using GC with a capillary column suggests:

• Poor injection technique causing splitless peak broadening
• Column bleed due to stationary phase degradation at high temperature
• Carrier gas flow too high
• Too low injector temperature

Correct Answer: Column bleed due to stationary phase degradation at high temperature

Q6. Which approach best addresses reversible column contamination by strongly retained polar impurities?

• Replace the entire column immediately
• Flush the column with a strong solvent pulse (e.g., high percent organic or basic/acidic wash) within column pH limits
• Increase flow rate permanently
• Store the column dry at high temperature

Correct Answer: Flush the column with a strong solvent pulse (e.g., high percent organic or basic/acidic wash) within column pH limits

Q7. Which maintenance item most effectively prevents particulate-induced column clogging?

• Frequent replacement of detector lamp
• Use of an appropriate guard column and inline filters
• Storing the column in methanol indefinitely
• Always running at maximum flow rate to clear particles

Correct Answer: Use of an appropriate guard column and inline filters

Q8. If peaks shift retention time gradually over many runs, a likely cause is:

• Column equilibration or mobile phase composition drift
• Injector septum leak only
• Detector wavelength fluctuation
• Changing sample concentration randomly

Correct Answer: Column equilibration or mobile phase composition drift

Q9. What is the most probable reason for ghost peaks appearing intermittently in chromatograms?

• System contamination or carryover from previous injections or solvents
• Column particle size distribution changes
• Too low detector sensitivity
• Incorrect column temperature programming

Correct Answer: System contamination or carryover from previous injections or solvents

Q10. Long-term loss of column efficiency (reduced theoretical plates) is usually due to:

• Accumulation of strongly adsorbed impurities and stationary phase degradation
• Overuse of guard columns
• Using mobile phase at recommended pH
• Too frequent column flushing

Correct Answer: Accumulation of strongly adsorbed impurities and stationary phase degradation

Q11. Which of the following is an appropriate first diagnostic step when you observe selective loss of late-eluting peaks?

• Decrease column temperature below recommended minimum
• Check for column contamination or voids and perform a high-organic wash
• Always replace the detector
• Change sample solvent to pure water without validation

Correct Answer: Check for column contamination or voids and perform a high-organic wash

Q12. Which practice can cause irreversible damage to silica-based HPLC columns?

• Exceeding the column’s recommended pH limits frequently
• Using filtered and degassed mobile phases
• Operating within recommended temperature and flow limits
• Equilibrating the column thoroughly after mobile phase changes

Correct Answer: Exceeding the column’s recommended pH limits frequently

Q13. Peak splitting (double peaks) observed for a single analyte commonly indicates:

• Sample solvent is too weak relative to mobile phase strength
• Column voids or poor packing causing flow path irregularities
• Detector is set to wrong wavelength
• Mobile phase is freshly prepared

Correct Answer: Column voids or poor packing causing flow path irregularities

Q14. In reversed-phase HPLC, which change is most likely to improve retention for polar analytes without switching columns?

• Decrease organic solvent content in the mobile phase
• Increase column temperature drastically
• Use a larger injection volume only
• Change detector to mass spectrometry

Correct Answer: Decrease organic solvent content in the mobile phase

Q15. When sample carryover is suspected, which action would best confirm and reduce carryover?

• Inject blank runs after high concentration samples and use stronger wash solvents for injector and syringe
• Reduce column temperature to minimum
• Replace the column immediately
• Remove the guard column permanently

Correct Answer: Inject blank runs after high concentration samples and use stronger wash solvents for injector and syringe

Q16. A steep baseline drift during isocratic HPLC can be caused by:

• Ambient lab humidity only
• Detector lamp instability or changes in mobile phase composition (e.g., gradient remnants or solvent mixing issues)
• Using a guard column
• Running at low injection volume

Correct Answer: Detector lamp instability or changes in mobile phase composition (e.g., gradient remnants or solvent mixing issues)

Q17. Which remedy is most suitable for reducing tailing caused by metal chelation of analytes in LC?

• Switch to a column with metallic frits only
• Add trace level complexing agents (e.g., EDTA) or use column with deactivated metal surfaces
• Increase sample concentration
• Always run at extremely high pH

Correct Answer: Add trace level complexing agents (e.g., EDTA) or use column with deactivated metal surfaces

Q18. If early-eluting peaks are missing while later peaks are present, the most likely cause is:

• Pre-column filter or guard column blockage selectively retaining early-eluting compounds
• Column temperature too high for all analytes
• Detector wavelength set too high
• Column particle size too small

Correct Answer: Pre-column filter or guard column blockage selectively retaining early-eluting compounds

Q19. Which practice best prevents irreversible contamination when analyzing samples with high protein content?

• Inject unfiltered samples to test column robustness
• Use sample pre-treatment (centrifugation/filtration), guard column and backflush when appropriate
• Store column in mobile phase containing untreated biological matrix
• Always use maximum injection volume allowed by autosampler

Correct Answer: Use sample pre-treatment (centrifugation/filtration), guard column and backflush when appropriate

Q20. Which factor should be checked first if column performance declines after changing mobile phase supplier or lot?

• Detector lamp alignment
• Mobile phase composition, pH, buffer strength, and quality (solvent grade/contaminants)
• Column oven calibration only
• Autosampler injection speed

Correct Answer: Mobile phase composition, pH, buffer strength, and quality (solvent grade/contaminants)

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