Effects of trimethylsilylation of copper(II)-phthalocyanine sulfonyl-aminopropyl silica gels on the separation of π-electron-rich compounds by high-performance liquid chromatography

As an attempt to elucidate the factor(s) responsible for the poor performance of a copper(II)-phthalocyanine aminopropyl-silica gels (Cu-PCS_D) column for HPLC, the silanol and/or amino groups remaining on Cu-PCS_D were endcapped with trimethylchlorosilane (TMCS) or N-trimethylsilylimidazole (TMSI). The trimethylsilylated Cu-PCS_Ds (Cu-PCS_D-TMCS and -TMSI) were investigated concerning their performance as an HPLC-stationary phase in the separation of πelectronrich polyaromatic hydrocarbons (PAHs), such as mutagenic anthracene and pyrene. As a result, trimethylsilylation with TMSI, which reacts only with silanol-groups, was not effective to improve the column efficiency. In contrast, trimethylsilylation by TMCS, which reacts with both the silanol- and amino-groups, improved the theoretical plate numbers (N) for PAHs separation with the Cu-PCS_D column, indicating that the low N values on the Cu-PCS_D column were caused by electrostatic interactions between PAHs and the remaining amino-groups on Cu-PCS_D. Furthermore, the retention data of mutagenic heterocyclic amines (HCAs) indicated that the remaining amino groups interact with the polar groups of HCAs.