Abstract
Strongly basic polyethylenimines (PEI) were coated on both untreated and diol-bonded silica particles. The resultant basic surface was found suitable for the separation of strongly basic alkylamines such as α-phenylethylamines with a pKb of ca. 4, under supercritical fluid chromatography (SFC) conditions with neat carbon dioxide. Interactions between the coated PEI and the silanol groups on the silica surface provided a stable coating. The acidic silica surface was neutralized by the basic amine functionalities in the PEI. Preliminary surface deactivations before coating with the basic PEI and subsequent end capping with hexamethyldisilazane (HMDS) were found necessary to obtain inert packing materials. However, it was found that the basic particle surface was not suitable for the separation of proton-donor compounds, including some weakly acidic phenols (pKa ca. 10). The effects of temperature on retention factors and peak shapes were studied. The stability of the PEI-coated particles was investigated by measuring the loss of organic carbon content of the particles after washing with supercritical CO2. It was found that the strong basicity and the extremely high molecular weight of the coated PEI produced stable coatings under SFC conditions. © 1997 John Wiley & Sons, Inc. J Micro Sep8: 519–528, 1996
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