Answer Posted / bhupalreddy

In chromatography silanol groups (Si-OH) at the
surface of silica gel are reacted with substituted Chloro
Silanes.

CH3 CH3
| | | |
--Si–OH + Cl - Si--R → --Si-O - Si - R
| | | |
CH3 CH3

By changing characteristics of group i.e. from changing R
from C1 to C18 we can alter the nature of stationary phase
from polar to non polar. Since C18 columns is non polar.
This helps separating various combinations of polar – non
polar constituents from the analyte.
C-8 columns contain 8 carbons and C-18 contains 18
carbons are attached to silicon group to form stationary
phases for chromatography. The C-18 columns are highly
Non polar compared to C-8 columns and most of the compounds
are well separated in C-18 carbon packed columns.

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