Final answer:
In normal-phase high-performance liquid chromatography (HPLC), the stationary phase is usually polar, such as silica, and the mobile phase is a non-polar solvent. The separation of compounds occurs due to their differential affinity to the stationary and mobile phases.
Step-by-step explanation:
In normal-phase high-performance liquid chromatography (HPLC), the stationary phase typically consists of a polar material such as silica particles, and the mobile phase is usually a non-polar solvent or solvent mixture. The principle of separation in HPLC is based on the differential affinity of the solutes to the stationary and mobile phases. Substances with a stronger affinity for the stationary phase travel more slowly through the column, while those with a greater affinity for the mobile phase elute faster. This allows for the separation of compounds based on their polarity and interactions with the stationary and mobile phases.
For example, during the experimental procedure of phosphatidylcholine separation using reverse phase HPLC, where the stationary phase is a C-18 column equilibrated with 98% methanol and 2% water, more hydrophobic solutes will interact strongly with the hydrophobic stationary phase and elute slower, thus achieving separation.