In a chromatographic system in which the stationary phase is a liquid layer adsorbed on packing and the mobile phase is a gas, which system is being described?

• A. Thin-layer
• B. High-performance liquid
• C. Ion-exchange
• D. Gas-liquid

Answer: (D)

Gas-liquid chromatography. Here the stationary phase is a liquid film adsorbed on the packing inside a column, and the mobile phase is an inert gas that carries the analytes through the column. Separation occurs as compounds partition between the liquid stationary phase and the gas mobile phase: those that dissolve more in the liquid spend more time in the stationary phase and elute later, while those that prefer the gas move through faster. The extent of this partitioning is governed by the partition coefficient, along with temperature and the properties of the liquid stationary phase. This setup is distinct from thin-layer chromatography, which has a solid stationary phase with a liquid mobile phase, and from typical high-performance liquid chromatography, which uses a liquid mobile phase with a column packed with a (usually solid) stationary phase.