NEW STATIONARY PHASES OF CONJUGATED PI-ELECTRON SYSTEMS FOR HPLC - CHARACTERIZATION OF STRUCTURE AND DYNAMICS BY SOLID-STATE NMR-SPECTROSCOPY

Four new stationary phases for HPLC were prepared by modifying silica gel with a trifunctional aminoalkyl silane. A conjugated pi-electron s ystem was linked to the amino group either directly or with a carboxyl ic anhydride as a spacer in between. Characterization and dynamic meas urements of the new stationary phases were performed by solid state NM R spectroscopy. The results of the Si-29 and C-13 CP/MAS techniques we re compared with the recently developed H-1 MAS-only technique. Despit e strong homonuclear dipole-dipole interactions it was possible to obt ain well resolved H-1 MAS spectra of those stationary phases with a hi gh degree of crosslinking. Limited mobility of the aromatic ligand fra gments is common for all examined stationary phases. The chromatograph ic properties of the new phases were tested by their ability to separa te a mixture of eight PAHs. It could be shown that the pi-pi interacti on mechanism is responsible for the separation of the eight PAHs, beca use the elution order of the PAHs did not change, despite the use of b oth a nonpolar mobile phase (n-heptane) and a polar mobile phase (meth anol/water mixture).