Modification of Selectivity in Reversed-Phase Liquid Chromatography of Polycyclic Aromatic Hydrocarbons Using Mixed Stationary Phases

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Abstract
Monomeric and polymeric C18 materials provide significantly different selectivities for polycyclic aromatic hydrocarbons (PAH) in reversed-phase liquid chromatography. Selectivity factors vary in a regular manner with respect to surface concentration of C18 groups on different C18 columns. In this study, we investigated the feasibility of “customizing” a C18 column to provide an intermediate selectivity by mixing 5-μm polymeric C18 material from two different lots with high and low C18 surface concentrations. Polymeric C18 materials from different production lots were mixed in ratios of 30/70, 50/50, and 70/30 (w/w). Selectivity factors for these columns were found to be similar to those predicted by the linear addition of the selectivities of the two individual phases. The PAH selectivities on these mixed columns were also found to be comparable to data obtained from coupled short columns of appropriate lengths each containing one of these different C18 materials. These studies indicate that columns of specific selectivity can be prepared by either mixing two different C18 materials or by coupling columns containing each of these different phases. The use of mixed phase columns is illustrated for the analysis of a fraction containing five condensed ring PAH isomers (molecular weight 278) isolated from an air particulate sample.