REVISIONIST LOOK AT SOLVOPHOBIC DRIVING FORCES IN REVERSED-PHASE LIQUID-CHROMATOGRAPHY .4. PARTITIONING VS ADSORPTION MECHANISM ON VARIOUS TYPES OF POLYMERIC BONDED PHASES

The partition and adsorption mechanisms of retention in reversed-phase liquid chromatography have been examined based on a comparison of the free energy of transfer of methylene groups from aqueous-organic mixt ures to bulk hexadecane with those to a variety of polymeric bonded ph ases. The stationary phases studied include: conventional silica-based polymeric phases of various alkyl chain lengths, a so-called ''horizo ntally polymerized'' octadecyl phase on silica and a series of polybut adiene-coated zirconia phases. The data indicate that for methylene gr oups a partition-like mechanism is dominant on all phases. On the poly butadiene-coated zirconia and ''horizontally polymerized'' octadecyl p hases the partition mechanism holds at all mobile phase compositions. In contrast on conventional polymeric silica phases the retention mech anism seems to become more adsorption-like at methanol compositions gr eater than about 70% (v/v).