RP-Modified Silica Plates
Reversed-phase (RP) modified silica HPTLC plates provide additional selectivities and significantly broaden thin-layer chromatography applications. Hence, they are well suited for demanding HPTLC separations, and as a pilot technique for HPLC. RP-2, RP-8, and RP-18 plates are based on silica gel 60, modified with aliphatic hydrocarbons. The chain length, combined with the degree of modification, defines the plate’s ability to tolerate the water of the solvent system, and strongly affects retention. Using the same solvent system, migration time increases in the order: RP-2, RP-8, RP-18.
RP-2 HPTLC sorbents exhibit higher polarity and a high affinity to aqueous solutions, tolerating up to 80% water. In contrast, the longer carbon chains, RP-8 and RP-18, can be run with up to 60% water in the solvent system. The specially developed RP-18W HPTLC plate offers a lower degree of surface modification, hence it can be used even with 100% water in the solvent system.