n-alkyl fluorenyl phases in chromatography - II. Dynamic behavior and high-performance liquid chromatography applications

The dynamic behavior of two n-hexyl fluorenyl phases (fluorene-6A [3a(T-n)( Q(m))(y)], fluorene-6B [3b(T-n)(Q(m))(y)]) and three n-decyl fluorenyl phas es (fluorene-10A [4a(T-n)(Q(m))(y)], fluorene-10B [4b(T-n)(Q(m))(y)], and f luorene-10C [4c(M-1)(Q(m))(y)]) is investigated by solid-state nuclear magn etic resonance (NMR) spectroscopy using the dipolar filter technique with b oth C-13 and H-1 detection. These results are compared with those from othe r dynamic measurements, Like the relaxation times in the rotating frame (T- 1 rho H) and the variation of the contact time (T-CH). Additionally, anothe r type of a fluorenyl phase [5a(T-n)(Q(m))(y)], which has an aromatic moiet y connected to the silica gel by amido couplings, was also investigated by the dipolar filter method. The solid-state NMR dynamic measurements indicat e an increased mobility of the n-alkyl fluorenyl phases compared to the ami do coupled fluorenyl phase. The lower the ligand density of the studied n-a lkyl fluorenyl phases, the higher their mobility. The separation behavior o f the respective phases in high-performance liquid chromatography was inves tigated with samples containing polycyclic aromatic hydrocarbons and nitro explosives. Depending on the amount of the chemically bound aromatic moiety and the length of their n-alkyl spacer groups, pi-pi interactions with the solute molecules are involved in the separation process and cause it to pr oceed at a different rate. Therefore, n-alkyl fluorenyl phases can be class ified as mixed-mode phases. (C) 1999 Elsevier Science B.V. All rights reser ved.