SELECTIVITY OF POLYMER-COATED ALUMINA STATIONARY PHASES FOR REVERSED-PHASE LIQUID-CHROMATOGRAPHY .1. METHYLENE GROUP SELECTIVITY

The methylene selectivity of various polymer-coated alumina columns [p olybutadiene (PBD), and polymeric CN and C-18 phases] are compared wit h those for three conventional silica bonded-phase C-18 columns. Reten tion and selectivity data were obtained using hydroorganic mixtures of acetonitrile and methanol for selected aromatic and aliphatic compoun ds, including n-2-ketones (C-4-C-9), n-alkylphenones (C-8-C-11), n-alk ylbenzenes (C-7-C-15), and n-alkanes (C-5-C-7). For a given mobile pha se, the polymer-coated alumina columns and silica based C-18 columns e xhibited similar methylene selectivity, although the alumina columns w ere much less retentive. The latter characteristic suggests a potentia lly important advantage of polymer-coated aluminas, namely that for a given homologous series it should be possible to employ a weaker mobil e phase on the polymer-coated columns, thereby achieving higher methyl ene selectivity with equivalent retention. The inherent selectivity ad vantage of the different polymer-coated aluminas may be especially imp ortant when separation selectivity is to be optimized by changing colu mns.