Normal phase HPLC is characterized by what?

• A. Polar stationary phase and non-polar mobile phase
• B. Non-polar stationary phase and polar mobile phase
• C. Both stationary and mobile phases polar
• D. Both polar and non-polar phases non-polar

Answer: (A)

Normal-phase HPLC separates compounds based on polarity, using a polar stationary phase and a nonpolar mobile phase. The stationary phase, such as silica or alumina, has polar groups that strongly interact with polar analytes. The mobile phase is relatively nonpolar, so nonpolar compounds dissolve and travel through the column quickly, while polar compounds spend more time adsorbed on the stationary phase and elute later. This means polar compounds are retained longer and nonpolar ones come out earlier. In practice, solvents like hexane (nonpolar) are used, sometimes with small amounts of a polar modifier to tweak retention. In contrast, reversed-phase HPLC uses a nonpolar stationary phase and a polar mobile phase, which is the opposite arrangement.