GC columns and types MCQs With Answer

Introduction: This quiz set on GC columns and types is designed for M.Pharm students preparing for Advanced Instrumental Analysis (MPA 201T). It provides focused, exam-oriented multiple-choice questions emphasizing column classifications (packed vs. capillary), stationary phase chemistries, capillary formats (WCOT, PLOT, SCOT), column dimensions, film thickness, selectivity, column performance parameters (HETP, theoretical plates, Van Deemter considerations), column bleeding and conditioning, and specialized columns (chiral, ionic liquid, porous). Each question highlights practical implications for method development, compound classes, and troubleshooting in pharmaceutical analysis. Use these MCQs to test conceptual understanding and to strengthen decision-making when selecting columns for real-world GC assays.

Q1. Which description best distinguishes a WCOT capillary column from a SCOT capillary column?

• WCOT has a porous support layer coated with stationary phase; SCOT has the stationary phase coated directly on the inner wall
• WCOT has the stationary phase coated directly on the inner wall; SCOT uses a solid support coated onto the wall which is then coated with stationary phase
• Both WCOT and SCOT are packed columns with particulate stationary phase
• WCOT and SCOT are identical; the terms are interchangeable

Correct Answer: WCOT has the stationary phase coated directly on the inner wall; SCOT uses a solid support coated onto the wall which is then coated with stationary phase

Q2. Which stationary phase would you choose for separating structurally similar nonpolar hydrocarbons by GC?

• Polyethylene glycol (PEG)
• 30% Phenyl methylpolysiloxane (midpolarity)
• 100% Methylpolysiloxane (nonpolar)
• Carbowax with high polarity

Correct Answer: 100% Methylpolysiloxane (nonpolar)

Q3. In GC capillary columns, decreasing internal diameter at constant column length generally results in:

• Lower efficiency (fewer theoretical plates)
• Higher sample capacity but lower resolution
• Increased efficiency (more theoretical plates) and faster analysis
• Increased column bleed at high temperature

Correct Answer: Increased efficiency (more theoretical plates) and faster analysis

Q4. Which column type is most appropriate for analysis of permanent gases and very volatile small molecules?

• WCOT coated with thick nonpolar film
• PLOT (Porous Layer Open Tubular) column
• SCOT with a polar liquid stationary phase
• Packed column with 1–2 µm particles

Correct Answer: PLOT (Porous Layer Open Tubular) column

Q5. What is the primary effect of increasing stationary phase film thickness in a capillary column?

• Decreased retention for high-boiling analytes
• Increased column efficiency (reduced HETP)
• Increased capacity and retention, especially for higher boiling or more polar analytes
• Reduced selectivity between polar and nonpolar compounds

Correct Answer: Increased capacity and retention, especially for higher boiling or more polar analytes

Q6. Which statement about column bleed is correct?

• Column bleed is desirable for baseline stability in MS detectors
• High column bleed indicates thermal decomposition or poor stationary phase purity and complicates MS detection
• Column bleed is unrelated to maximum operating temperature
• Bleed only occurs in packed columns, not in capillary columns

Correct Answer: High column bleed indicates thermal decomposition or poor stationary phase purity and complicates MS detection

Q7. For trace analysis of pesticides in splitless injection, which column characteristic is most important?

• Very wide internal diameter (>0.53 mm) to increase sample load
• Thin film thickness to minimize retention of semi-volatile analytes
• Low polarity stationary phase regardless of analyte polarity
• Good column inertness (deactivation) and suitable polarity for analytes

Correct Answer: Good column inertness (deactivation) and suitable polarity for analytes

Q8. Which stationary phase would typically provide strong retention and selectivity for polar analytes such as alcohols and acids?

• 100% dimethylpolysiloxane
• Polyethylene glycol (PEG, e.g., Carbowax)
• 1% phenyl, 99% methylpolysiloxane
• Porous graphitized carbon

Correct Answer: Polyethylene glycol (PEG, e.g., Carbowax)

Q9. Which of the following best explains the effect of column length on resolution and analysis time?

• Longer columns decrease resolution and shorten analysis time
• Longer columns increase resolution but also increase analysis time and pressure drop
• Column length has no effect on resolution if internal diameter is constant
• Shorter columns always produce higher theoretical plates

Correct Answer: Longer columns increase resolution but also increase analysis time and pressure drop

Q10. Which capillary column is commonly used for chiral separations in gas chromatography?

• Polydimethylsiloxane without modifiers
• Columns coated with cyclodextrin derivatives
• PLOT columns packed with molecular sieves
• 100% methylphenyl polysiloxane nonpolar columns

Correct Answer: Columns coated with cyclodextrin derivatives

Q11. Which parameter is represented by HETP and how does it relate to column performance?

• Height Equivalent to a Theoretical Plate; smaller HETP means higher column efficiency
• Heat Equivalent to Temperature Peak; larger HETP means better thermal stability
• Hydrodynamic Equivalent Transfer Parameter; unrelated to efficiency
• Helium Efficiency Transfer Potential; only relevant for helium carrier gas

Correct Answer: Height Equivalent to a Theoretical Plate; smaller HETP means higher column efficiency

Q12. Which stationary phase chemistry would best separate aromatic isomers with slight polarity differences?

• 100% methylpolysiloxane
• Cyanopropylphenyl or phenyl-containing polysiloxane
• Strongly polar PEG phase only
• PLOT column with inorganic adsorbent

Correct Answer: Cyanopropylphenyl or phenyl-containing polysiloxane

Q13. What is a significant advantage of ionic liquid stationary phases in GC?

• Extremely low polarity suitable only for hydrocarbons
• Wide thermal stability window and unique selectivity for polar and polarizable compounds
• They are identical to PEG phases but cheaper
• High bleed at low temperatures making them unsuitable for MS

Correct Answer: Wide thermal stability window and unique selectivity for polar and polarizable compounds

Q14. When choosing a guard column or retention gap, the primary purpose is to:

• Increase column bleed to clean the detector
• Protect the analytical column from nonvolatile contaminants and improve peak shapes for solvent-focused injections
• Convert a capillary into a packed column
• Reduce the column’s maximum operating temperature

Correct Answer: Protect the analytical column from nonvolatile contaminants and improve peak shapes for solvent-focused injections

Q15. Which of the following best describes the selectivity difference between polar and nonpolar stationary phases?

• Polar phases generally increase retention of polar analytes via dipole–dipole and hydrogen bonding interactions, while nonpolar phases retain analytes primarily by dispersion forces
• Nonpolar phases form hydrogen bonds with analytes while polar phases do not
• Polar and nonpolar phases have identical retention mechanisms; only film thickness matters
• Nonpolar phases are always better for separating isomers than polar phases

Correct Answer: Polar phases generally increase retention of polar analytes via dipole–dipole and hydrogen bonding interactions, while nonpolar phases retain analytes primarily by dispersion forces

Q16. For GC–MS analysis where sensitivity for trace polar pesticides is required, which column property is most critical?

• High bleed at analysis temperature to increase ionization
• Excellent deactivation (inertness) to prevent adsorption and losses of active polar analytes
• Thick nonpolar film to avoid retention of polar analytes
• Use of a PLOT column regardless of analyte chemistry

Correct Answer: Excellent deactivation (inertness) to prevent adsorption and losses of active polar analytes

Q17. Which capillary column type is optimal for analysis of high-boiling, thermally labile compounds using on-column cold injection?

• Packed column with stainless steel tubing
• WCOT column with a thermally stable stationary phase and deactivated surface
• PLOT column with inorganic adsorbent
• SCOT with thick porous support that adsorbs analytes strongly

Correct Answer: WCOT column with a thermally stable stationary phase and deactivated surface

Q18. How does phase ratio (beta, β = column volume of carrier gas/stationary phase volume) influence retention and sample capacity?

• Higher β (thin film or large ID) increases retention and capacity
• Lower β (thicker film or smaller ID) increases retention and capacity for condensable analytes
• β has no effect on retention, only on column bleed
• Only column length influences β

Correct Answer: Lower β (thicker film or smaller ID) increases retention and capacity for condensable analytes

Q19. Which operational choice reduces on-column adsorption and improves peak shape for active compounds?

• Using an unconditioned column and increasing injector temperature
• Using properly deactivated (silanized) column surface and optimized inlet liner or on-column injection
• Selecting the thinnest possible film regardless of analyte volatility
• Always using hydrogen carrier gas instead of helium

Correct Answer: Using properly deactivated (silanized) column surface and optimized inlet liner or on-column injection

Q20. Which column material is most commonly used for modern flexible capillary columns and offers low bleeding and chemical inertness?

• Glass-lined stainless steel tubing
• Fused silica coated with polyimide protective layer
• Pure glass capillary without coating
• Aluminum tubing with silica gel packing

Correct Answer: Fused silica coated with polyimide protective layer

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