Liquid Chromatography - Bonded Phase Synthesis by Reaction in a Solvent 2


The carbon content of a bonded phase is often used to determine the efficacy of bonding, but its value must be used in conjunction with a knowledge of the surface area of the native silica in order to arrive at a meaningful conclusion. The amount of material bonded to the silica will depend, not only on the efficiency of the reaction, but also on the number of silanol groups that were available with which it could react; ipso facto it will also depend on the surface area of the parent silica. The carbon content of the bonded phase is usually determined by micro-analysis and the result expressed as %w/w of the combined bonded organic material and the silica gel. Consider a bonded phase where the carbon content is (y)%w/w coated with a hydrocarbon

moiety having (n) carbon atoms per aliphatic chain (e.g., for the dimethyl octyl brush phase, n=10). Then, the concentration of aliphatic chains in mols. per gram of silica (m')will be,

Consequently, if the surface area of the silica is (A) m2g-1, the number of mols of aliphatic chains (m) in micromols per square meter will be given by,