Which statement correctly describes normal-phase chromatography (NPC) and reversed-phase chromatography (RPC) in terms of stationary/mobile phases and the retention of nonpolar analytes?

Which statement correctly describes normal-phase chromatography (NPC) and reversed-phase chromatography (RPC) in terms of stationary/mobile phases and the retention of nonpolar analytes?

• A. NPC uses polar stationary phases with nonpolar mobile phases; RPC uses nonpolar stationary phases with more polar mobile phases; Nonpolar analytes are retained longer in RPC.
• B. NPC uses nonpolar stationary phases; RPC uses polar stationary phases; Nonpolar analytes are retained longer in NPC.
• C. NPC and RPC use the same stationary phase; retention of nonpolar analytes is identical.
• D. NPC uses polar mobile phases; RPC uses nonpolar mobile phases; Retention is independent of polarity.

Answer: (A)

Retention in chromatography is governed by how strongly the analyte prefers the phase it’s in, which depends on polarity. In normal-phase chromatography, the stationary phase is polar and the mobile phase is relatively nonpolar. Polar analytes interact strongly with the polar stationary phase and are retained longer, while nonpolar analytes favor the nonpolar mobile phase and elute more quickly. In reversed-phase chromatography, the stationary phase is nonpolar and the mobile phase is more polar. Nonpolar (hydrophobic) analytes have a strong affinity for the nonpolar stationary phase and are held back longer, whereas polar analytes partition into the polar mobile phase and elute sooner. So nonpolar analytes are retained longer in reversed-phase chromatography, which matches the statement.

Retention in chromatography is governed by how strongly the analyte prefers the phase it’s in, which depends on polarity.

In normal-phase chromatography, the stationary phase is polar and the mobile phase is relatively nonpolar. Polar analytes interact strongly with the polar stationary phase and are retained longer, while nonpolar analytes favor the nonpolar mobile phase and elute more quickly.

In reversed-phase chromatography, the stationary phase is nonpolar and the mobile phase is more polar. Nonpolar (hydrophobic) analytes have a strong affinity for the nonpolar stationary phase and are held back longer, whereas polar analytes partition into the polar mobile phase and elute sooner.

So nonpolar analytes are retained longer in reversed-phase chromatography, which matches the statement.