Preparation of nitrophenylethylsilylated silica gel and its chromatographic properties, in the separation of polychrlorinated dibenzo-p-dioxins

Nitrophenylethylsilylated (NPE) silical gel was prepared from phenylethylsilylated silica gel by direct nitration, and its chromatographic properties were compared with those of C₁₈ and pryrenylethyl (PYE) bonded phase in reversed-phase high-performance liquid chromatography. The NPE phase showed preferential retention for aromatic compounds, especially for those with dipolar character. In contrast, PYE phase showed preferential retention for symmetrically substituted aromatic compounds. The combination of NPE and PYE phases provided the selectivity required for the separation of isomers of polychlorinated aromatic compounds, namely polychlorobenzo-p-dioxins (PCDDs). The two stationary phases, having aromatic functionalities of opposite nature, also provided the possibility of structural assignment of PCDD isomers based on the chromatographic retention on the two phases.