Reversed-phase HPLC setup: Which pairing correctly describes the polarity of solvent (mobile phase) and column (stationary phase)?

Introduction / Context:
Reversed-phase HPLC (RP-HPLC) is the most widely used HPLC mode for small molecules. It inverts the polarity arrangement relative to classical normal-phase chromatography.

Given Data / Assumptions:

• Stationary phase: non-polar (e.g., C18, C8 alkyl-bonded silica).
• Mobile phase: relatively polar (e.g., water mixed with methanol or acetonitrile).
• Analyte retention increases with hydrophobicity.

Concept / Approach:
In RP-HPLC, non-polar analytes interact more strongly with the hydrophobic stationary phase and elute later, while polar analytes elute earlier in polar aqueous-organic mobile phases. This is the opposite of normal-phase, where a polar stationary phase and non-polar mobile phase are used.

Step-by-Step Solution:
Identify the hallmark of reversed-phase: non-polar stationary phase.Recognize that mobile phases are polar mixtures (water + organic modifier).Select the polar solvent/non-polar column pairing.

Verification / Alternative check:
Column manufacturer guides specify C18 columns with water–acetonitrile or water–methanol gradients—clear evidence of polar mobile phase and non-polar stationary phase.

Why Other Options Are Wrong:

• Non-polar solvent/polar column describes normal-phase, not reversed-phase.
• Non-polar/non-polar is not a standard chromatographic mode.
• “Any of the above” is incorrect because reversed-phase has a specific polarity arrangement.

Common Pitfalls:
Confusing reversed-phase with hydrophilic interaction liquid chromatography (HILIC), which uses a polar stationary phase but different retention mechanism.

Final Answer:
polar solvent/non-polar column