Selectivity of polymer-coated alumina stationary phases for reversed-phase liquid chromatography. Part 1. Methylene group selectivity

Abstract

The methylene selectivity of various polymer-coated alumina columns [polybutadiene (PBD), and polymeric CN and C₁₈ phases] are compared with those for three conventional silica bonded-phase C₁₈ columns. Retention and selectivity data were obtained using hydroorganic mixtures of acetonitrile and methanol for selected aromatic and aliphatic compounds, including n-2-ketones (C₄–C₉), n-alkylphenones (C₈–C₁₁), n-alkylbenzenes (C₇–C₁₅), and n-alkanes (C₅–C₇). For a given mobile phase, the polymer-coated alumina columns and silica based C₁₈ columns exhibited similar methylene selectivity, although the alumina columns were much less retentive. The latter characteristic suggests a potentially important advantage of polymer-coated aluminas, namely that for a given homologous series it should be possible to employ a weaker mobile phase on the polymer-coated columns, thereby achieving higher methylene selectivity with equivalent retention. The inherent selectivity advantage of the different polymer-coated aluminas may be especially important when separation selectivity is to be optimized by changing columns.