Which gas is NOT listed as a mobile phase in the source material for gas chromatography?

• A. Hydrogen
• B. Helium
• C. Argon
• D. Oxygen

Answer: (D)

In gas chromatography, the mobile phase (the carrier gas) must transport the sample through the column without reacting with the analytes or the stationary phase. Oxygen is reactive and would oxidize many compounds, potentially altering their behavior, damaging the column, and interfering with detectors. That’s why oxygen is not listed as a mobile phase. The gases typically used—hydrogen, helium, and sometimes argon—are chosen because they are inert enough under GC conditions to move analytes safely through the column, with each gas offering different performance characteristics.