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 phases (fluorene-10A [4a(T-n)(Q(m))(y)], fluorene-10B [4b(T-n)(Q(m))(y)], and fluorene-10C [4c(M-1)(Q(m))(y)]) is investigated by solid-state nuclear magnetic resonance (NMR) spectroscopy using the dipolar filter technique with both C-13 and H-1 detection. These results are compared with those from other dynamic measurements, Like the relaxation times in the rotating frame (T-1 rho H) and the variation of the contact time (T-CH). Additionally, another type of a fluorenyl phase [5a(T-n)(Q(m))(y)], which has an aromatic moiety connected to the silica gel by amido couplings, was also investigated by the dipolar filter method. The solid-state NMR dynamic measurements indicate an increased mobility of the n-alkyl fluorenyl phases compared to the amido coupled fluorenyl phase. The lower the ligand density of the studied n-alkyl fluorenyl phases, the higher their mobility. The separation behavior of the respective phases in high-performance liquid chromatography was investigated 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 proceed at a different rate. Therefore, n-alkyl fluorenyl phases can be classified as mixed-mode phases. (C) 1999 Elsevier Science B.V. All rights reserved.