Analytical chemistry — In normal-phase HPLC (high-performance liquid chromatography), which pairing best describes the mobile phase and the stationary phase (column) used?

Introduction / Context:Normal-phase HPLC is a classic chromatographic mode that separates analytes primarily by polarity using a polar stationary phase and a relatively non-polar mobile phase. Knowing how phases are paired is essential for choosing solvents, predicting elution order, and troubleshooting retention problems.

Given Data / Assumptions:

• The question asks about normal-phase HPLC configuration.
• Stationary phase: typically polar (e.g., bare silica with surface silanols).
• Mobile phase: typically non-polar or weakly polar organic solvents (e.g., hexane with small percentages of isopropanol or ethyl acetate modifiers).

Concept / Approach:In normal-phase mode, polar analytes interact strongly with the polar stationary phase and elute later. Less polar analytes spend more time in the non-polar mobile phase and elute earlier. This is the inverse of reversed-phase HPLC, where a non-polar stationary phase is paired with a polar (water-rich) mobile phase.

Step-by-Step Solution:

Verification / Alternative check:Method development guides differentiate normal-phase (polar stationary, non-polar mobile) from reversed-phase (non-polar stationary, polar mobile). Typical solvent systems for normal phase confirm the non-polar mobile phase choice.

Why Other Options Are Wrong:

• Polar solvent / non-polar column describes reversed-phase, not normal-phase.
• Non-polar solvent / non-polar column does not create useful polarity-based separation.
• Any of the above is incorrect because normal-phase has a specific pairing.
• Polar solvent / polar column would lead to very strong retention and is not the standard definition.

Common Pitfalls:Confusing normal-phase with reversed-phase; assuming “normal” means water-based. In chromatography, “normal” historically refers to the early silica-based method, not to aqueous systems.

Final Answer:non-polar solvent / polar column