Preparation of Various Bonded Phases for HPLC Using Monochlorosilanes

Monochlorosilanes have been prepared with yields of about 80% through a catalytic hydrosilylation of terminal olefins. Subsequently, the silanes are chemically bonded to silica to obtain: (i) n-octyldimethylsilyl bonded phases with reproducible surface coverage ranging from 0.8 to 3.5 μmol/m2, (ii) propyldimethylsilyl bonded phases with different functional groups at the γ-position, all showing a nearly equal surface coverage of some 3.3 μmol/m2, and (iii) n-alkyldimethylsilyl bonded phases with chainlengths ranging from 1 to 22 carbon atoms and with surface coverages ranging from 3.9 μmol/m2 for RP-1 to 3.0 μmol/m2 for the RP-22 bonded phase. A simplified model based on the pore structure of silica allows an explanation and estimation of the maximum surface coverage as a function of the chainlength of the bonded phase.