SFC instrumentation MCQs With Answer

Introduction: SFC instrumentation MCQs With Answer is designed to help M.Pharm students deepen their understanding of supercritical fluid chromatography (SFC) instrumentation. This collection focuses on practical and theoretical aspects of SFC hardware: CO2 delivery and pumps, backpressure regulators, restrictors, column and detector interfacing, modifiers, and operational variables that affect retention and selectivity. The questions emphasize interpretation of instrumentation choices, troubleshooting, and method design for pharmaceutical separations, especially chiral and nonpolar analytes. Use these MCQs to test conceptual knowledge, prepare for exams, and reinforce lab decision-making when setting up or optimizing SFC methods in advanced instrumental analysis courses.

Q1. What is the most commonly used primary mobile phase in analytical supercritical fluid chromatography?

• Liquid nitrogen
• Supercritical carbon dioxide (CO2) typically with an organic modifier
• Pure water at high pressure
• Helium gas

Correct Answer: Supercritical carbon dioxide (CO2) typically with an organic modifier

Q2. What is the primary function of the backpressure regulator (BPR) in SFC instrumentation?

• To heat the column to the desired temperature
• To maintain system pressure so CO2 stays in the supercritical state and control mobile-phase density
• To add organic modifier into the CO2 stream
• To measure detector response

Correct Answer: To maintain system pressure so CO2 stays in the supercritical state and control mobile-phase density

Q3. What are the critical temperature and pressure of carbon dioxide relevant for SFC operation?

• 0.01°C and 1.013 bar
• 31.1°C and 73.8 bar
• 100°C and 200 bar
• 4°C and 20 bar

Correct Answer: 31.1°C and 73.8 bar

Q4. Which organic solvent is most commonly used as a modifier in SFC to increase polarity of the mobile phase?

• n-Hexane
• Methanol (most commonly used as organic modifier)
• Carbon tetrachloride
• Sulfuric acid

Correct Answer: Methanol (most commonly used as organic modifier)

Q5. What pump arrangement is typically used to deliver CO2 and modifier in modern analytical SFC systems?

• A single low-pressure peristaltic pump for both CO2 and modifier
• Specialized high-pressure CO2 pump (syringe or piston) with a separate binary pump for modifier
• Only manual gravity feed
• Compressed air pump and vacuum pump in series

Correct Answer: Specialized high-pressure CO2 pump (syringe or piston) with a separate binary pump for modifier

Q6. What is the role of a restrictor tube in SFC systems?

• To increase column temperature rapidly
• To prevent flash evaporation by restricting flow at the column outlet and control pressure drop
• To mix CO2 and modifier thoroughly before injection
• To ionize analytes before MS detection

Correct Answer: To prevent flash evaporation by restricting flow at the column outlet and control pressure drop

Q7. Which detector is most commonly interfaced with SFC for structural and mass information, and often requires a make-up solvent?

• Refractive index detector
• Mass spectrometer (often with make-up solvent to improve ionization)
• Polarimeter only
• Conductivity detector

Correct Answer: Mass spectrometer (often with make-up solvent to improve ionization)

Q8. How does increasing the percentage of organic modifier in the CO2 mobile phase generally affect analyte retention?

• It decreases mobile-phase polarity and increases retention
• It increases mobile-phase polarity and decreases retention (faster elution)
• It has no effect on retention
• It causes immediate precipitation of analytes

Correct Answer: It increases mobile-phase polarity and decreases retention (faster elution)

Q9. Which type of stationary phases are most commonly used in packed analytical SFC columns?

• Silica-based bonded phases, including reversed-phase and chiral selectors
• Only polymeric C18 with no silica
• Pure metallic meshes
• Uncoated glass capillaries only

Correct Answer: Silica-based bonded phases, including reversed-phase and chiral selectors

Q10. What is the typical effect of increasing column temperature on CO2 density and chromatographic retention in SFC?

• Temperature increase raises CO2 density and always decreases retention
• Temperature increase reduces CO2 density and often increases retention due to reduced solvating power
• Temperature change has no effect on CO2 properties
• Temperature increase converts CO2 to gas and stops chromatography

Correct Answer: Temperature increase reduces CO2 density and often increases retention due to reduced solvating power

Q11. Is gradient elution possible in SFC, and what is a common approach to perform it?

• No, gradient elution is impossible in SFC
• Yes; perform a modifier (organic) gradient while maintaining CO2 delivery and controlling pressure with the BPR
• Yes; change the column packing during the run
• Yes; vary the CO2 temperature instantaneously to create a gradient

Correct Answer: Yes; perform a modifier (organic) gradient while maintaining CO2 delivery and controlling pressure with the BPR

Q12. Why is a make-up solvent often used between SFC and MS interfaces?

• To cool the MS source
• To provide a polar solvent and ions that enhance electrospray ionization and prevent CO2-induced signal suppression
• To dilute the analyte to below detection limits
• To react chemically with analytes to form new compounds

Correct Answer: To provide a polar solvent and ions that enhance electrospray ionization and prevent CO2-induced signal suppression

Q13. Which common instrumentation-related problem in SFC causes peak broadening and loss of efficiency?

• Excessively low detector sensitivity
• Flash expansion of CO2 due to insufficient backpressure or an inadequate restrictor
• Using water as the only modifier
• Overheating the autosampler tray

Correct Answer: Flash expansion of CO2 due to insufficient backpressure or an inadequate restrictor

Q14. Which is a primary advantage of SFC compared with conventional reversed-phase HPLC for nonpolar and chiral analytes?

• Higher solvent consumption and slower runs
• Faster separations, reduced organic solvent use, and often superior chiral resolution for suitable stationary phases
• Incompatibility with mass spectrometry
• Better performance only for highly ionic analytes

Correct Answer: Faster separations, reduced organic solvent use, and often superior chiral resolution for suitable stationary phases

Q15. What is a practical limitation of SFC when analyzing very polar or ionic compounds?

• They are always separated better in SFC than HPLC
• SFC generally has limited retention for highly polar/ionic analytes unless strong polar modifiers or specialized stationary phases are used
• Ionization becomes impossible in MS detection
• Column lifetime is infinite for polar analytes

Correct Answer: SFC generally has limited retention for highly polar/ionic analytes unless strong polar modifiers or specialized stationary phases are used

Q16. Where is the backpressure regulator (BPR) normally placed in an SFC instrument relative to the column and detector?

• Between the CO2 cylinder and the pump
• After the column and often before detector or splitting to detector, to maintain system pressure
• Inside the autosampler vial
• At the injector pin only

Correct Answer: After the column and often before detector or splitting to detector, to maintain system pressure

Q17. What are the typical units used to report SFC mobile-phase flow rates in analytical practice?

• Liters per hour exclusively
• Milliliters per minute (mL/min), often separately reporting CO2 and modifier flows
• Parts per million
• Molality (mol/kg)

Correct Answer: Milliliters per minute (mL/min), often separately reporting CO2 and modifier flows

Q18. Why is minimizing extra-column dead volume especially important in SFC instrumentation?

• Dead volume cools the column which is desirable
• Large dead volume causes peak broadening and loss of efficiency due to compressible mobile phase and expansion effects
• Dead volume increases detection sensitivity
• Dead volume is irrelevant for small molecules

Correct Answer: Large dead volume causes peak broadening and loss of efficiency due to compressible mobile phase and expansion effects

Q19. Why is preheating or temperature control of CO2 delivery lines important in SFC?

• To freeze the CO2 prior to injection
• To avoid local cooling/phase change and maintain consistent CO2 density and phase at the column inlet
• To oxidize analytes before separation
• To reduce detector sensitivity intentionally

Correct Answer: To avoid local cooling/phase change and maintain consistent CO2 density and phase at the column inlet

Q20. How does increasing backpressure generally affect CO2 density and chromatographic behavior in SFC?

• Increasing backpressure decreases CO2 density and increases retention
• Increasing backpressure increases CO2 density, increases solvating power, and typically decreases retention time
• Backpressure has no influence on CO2 properties
• Increasing backpressure always causes CO2 to liquefy and stops chromatography

Correct Answer: Increasing backpressure increases CO2 density, increases solvating power, and typically decreases retention time

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