RP-2, RP-8 and RP-18 are based on silica gel 60 modified with aliphatic hydrocarbons. The chain length, in combination with the degree of modification, defines the ability to tolerate water in the solvent system and strongly affects retention. Migration time increases in the order RP-2, RP-8 and RP-18 using the same solvent composition. RP-8 and RP-18 can be run with up to 60% water in the solvent system.

• Results less dependent on atmospheric humidity
• Allows the use of aqueous solvent systems
• RP-modified silica provides a ready correlation with HPLC