If it is water solubility target object, and it is weak-polar or middle polarity, you can choose C8 or C4 silica.

If it is water solubility target object, and it is middle polarity or strong polarity, you can choose C18 silica.

C4 and C18 reveals to you the quantity of carbon molecules in the fixed stage materials in siloxane gatherings. More the carbon iotas, more the nonpolarity of the stationary phase.

The length of the alkyl chain obviously matters. The more drawn out chains have a lot of maintenance over the more limited ones.

Likewise, longer chains permit the utilization of a lot bigger examples. For instance, you can twofold the example size in C18 segment that of C4 section under a similar condtions，C18 is preferred for less polar samples.