Final answer:
The mobile phase in HPLC is a solvent mixture that carries the sample through the column, with its composition being essential for the separation of solutes.
Step-by-step explanation:
The mobile phase of high performance liquid chromatography (HPLC) is the solution that is passed through the column, carrying the sample components with it. In HPLC, the mobile phase is usually a mixture of solvents, such as water, methanol, or acetonitrile, which can be modified with additives like formic acid. The choice of the mobile phase composition is crucial as it influences the retention time of the solutes and thus their separation based on their differential affinities to the stationary phase. The stationary phase, typically made of silica particles coated with alkane chains in reverse phase HPLC, interacts with the sample compounds. More hydrophobic compounds have a stronger interaction and therefore move more slowly through the column compared to their less hydrophobic counterparts.