Suspended-state HR/MAS NMR

Spinning rate = 4500 Hz Fig. 3. Experimental set-up of the suspended-state HR/MAS NMR rotor. 

Hence, this NMR technique allows us to record the NMR spectrum of a dissolved analyte in the presence of a chromatographic sorbent, and therefore mimic a static chromatographic situation. In the suspended-state HR/MAS NMR experiment, the resolution of the signals of the dissolved analyte will be comparable to that in a solution-state NMR experiment. HR/MAS NMR spectroscopy also allows the acquisition of H NMR spectra of stationary phases bonded to silica supports with high resolution compared to the corresponding solid-state NMR spectra. The HR/MAS H NMR spectrum of a (tert-butylcarbamoyl)quinine selector covalently bonded to silica, suspended in [DJmethanol, shows that a full structure elucidation of the selector is possible (see Fig. 4). 

Fig. 4. Suspended-state HR/MAS NMR spectrum of a chromatographic sorbent suspended in [DJmethanol.

Fig. 5. Suspended-state HR/MAS NMR spectra of (a) ( )-DBTA dissolved in CDQ, (b) ( )-DBTA dissolved in CDQ, in the presence of Kromasil-TBB.

Tables. Suspended-state HR/MAS-NMR T, measurements on (R)-8 and (S)-8 in the presence of Kromasil-DMB using [Dj]propan-2-ol (5%) in QD,2 as solvent.

Several difFerent suspended-state HR/MAS NMR experiments can be performed in order to obtain information aboutly exact where the interactions take place between an analyte and a sorbent. In Fig. 9, the suspended-state HR/MAS trNOESY spectrum of (S)-8 dissolved in CDCI3 in the presence of Kromasil-DMB, shown in Fig. 5, shows both negative intramolecular trNOE cross-peaks (black), confirming the interaction with the sorbent, and intermolecular (grey) cross-peaks between the aromatic residue in the selector and the aromatic ring in the analyte... 

The use of suspended-state HR/MAS NMR spectroscopy to study the interactions between chromatographic sorbents and analytes of interest is still in its infancy. 

Fig. 10. Suspended-state HR/MAS H NMR spectra of (A) free (S)-8 dissolved in CDCI3, and (B) (S)-8 dissolved in CDCI3 in the presence of Kromasil-DMB.

The phases of -butylvinyl ether (C4VE) and -octadecylvinyl ether (C18VE) crosslinked with triethylene glycol divinyl ether or divinylbenzene were investigated by means of solid-state CPMAS NMR and HR MAS NMR in suspended-state. ... 

Another, yet completely different access to macroscopic binding strengths of selectands on CSPs has been described by Hellriegel et al. [65] employing suspended-state NMR spectroscopy. Thus, HR-MAS 2D transfer-nuclear Overhauser effect spectroscopy (NOESY) was utilized to distinguish solutes strongly binding to the... 

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