The stationary phase in reversed phase chromatography is a linear saturated and alkane covalently bound to silica support, the length of which is different, and the longest is octadecyl, which is the most used stationary phase.
The hydrophobic character of linear saturated alkanes increases with the length of the hydrocarbon chain and the residence time of the solute due to hydrophobic interaction in the reversed phase column will also increase with the length of the hydrocarbon chain.
In general, this means that a reversed phase column with a hydrocarbon chain length can give a better resolution, in most cases relying on the repeated selection of the column. Since the stationary phase of reversed-phase chromatography is a hydrophobic hydrocarbon, the interaction between the solute and the stationary phase is mainly a non-polar interaction or a hydrophobic interaction, so the strength of the solvent increases as the polarity decreases.
Water is the most polar solvent and the weakest solvent in reversed-phase chromatography and a different concentration of a water-miscible organic solvent is often added to the base solvent to obtain mobile phases of different strengths, which are referred to as modifiers.
The most commonly used organic solvents are methanol and acetonitrile. In addition, ethanol, tetrahydrofuran, isopropanol, and dioxane are often used as modifiers.
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