A number of different stationary phases designed for hydrophobic interaction chromatography have been examined to assess their efficiency and resolving capability with respect to protein and peptide mixtures. A packing with an ether-bonded phase was substantially less hydrophobic than those with propyl- or phenyl-bonded surface chemistry. While the overall efficiencies of most columns were broadly similar with respect to most proteins, some proteins did chromatograph with enhanced efficiency on specific packings. The elution order of individual proteins was, with one or two exceptions, similar for all columns tested using comparable mobile phases. It differed, however, substantially from orders obtained with conventional reversed-phase alkyl-bonded phases and from the elution orders obtained when the hydrophobic packings were used in a reversed-phase mode, i.e. with an organic modifier gradient. Varying the salt used in the mobile phase and its pH under hydrophobic interaction conditions (high ionic strength) changed overall retentivities and also altered specific retention orders, thus offering possibilities of selective resolution of some mixtures.

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