What does gas chromatography do?

• A. Separates based on boiling point.
• B. Identifies molecular structure.
• C. Separates mixtures based on distribution between stationary liquid phase and mobile gas phase.
• D. Measures isotope ratios.

Answer: (C)

Gas chromatography separates components of a mixture by distributing them between a stationary liquid phase inside a column and a mobile inert gas that carries them through the column. Each compound reaches an equilibrium between the two phases, and those with stronger affinity for the stationary phase spend more time in the liquid and exit later, producing distinct retention times and separated peaks. This separation arises from partitioning between the two phases, not simply from boiling point, though volatility influences how readily a compound enters the gas phase. Identification or quantification is then achieved with detectors or standards (for example, a mass spectrometer or flame ionization detector), rather than by GC alone, and isotope ratios require different techniques.