Among partition chromatography methods that perform separation based on the partition equilibrium of a third component (sample) between two immiscible phases (stationary phase-mobile phase), the method that uses a stationary phase with higher polarity than that of the mobile phase is called normal-phase partition chromatography. In contrast, the type of partition chromatography that uses a stationary phase with lower polarity than that of the mobile phase is called reversed-phase partition chromatography.
NH2 (aminopropyl group) and CN (cyanopropyl group) packing materials can be used in both normal-phase and reversed-phase modes. In most cases, they are used in the normal-phase mode when the sample is a low molecular weight compound with high polarity, and in the reversed-phase mode when the polarity of the sample is low.