Two compounds have similar volatility at the run temperature. Under the same GC conditions, which generally elutes earlier?

• The one interacting more with the phase
• The one interacting less with the phase
• Both must leave at exactly the same time

What serves as the mobile phase in GC?

• A flowing carrier gas, such as helium
• A flowing liquid mixture, such as water
• A fixed stationary film, such as a polymer

A GC temperature programme can start cooler to retain early compounds, then raise the temperature to reduce late retention.

A hydroxyl-containing analyte has poor GC volatility. A proposed derivative may improve it. Which plan is justified before relying on the derivative method?

• Check derivative formation, stability and response
• Use the starting compound's calibration without retesting
• Assign every new peak to the derivative without a check

A low isothermal temperature resolves early compounds but leaves late compounds very delayed. Which trial addresses this trade-off?

• Raise the sample mass but keep the oven fixed
• Keep the low oven temperature for a longer run
• Raise the oven temperature later in the run

You need sensitive detection of trace organic compounds and do not need sample recovery. Which comparison supports choosing FID rather than TCD?

• TCD is usually more sensitive for these organic traces
• FID is usually more sensitive for these organic traces
• Both detectors have identical responses to all organic traces

With no flow split before an FID, unchanged analyte can be collected after it passes through the detector.

A concentrated GC sample gives fronting peaks. Dilution restores their shape at the same injection volume and settings. Which explanation is best supported?

• An injector leak proved by peak shape alone
• A permanent detector fault independent of mass
• Sample-mass overload in the concentrated run