Combined rotation and multi-pulse

Combined rotation and multi-pulse spectroscopy CRAMPS... 

To measure high-resolution spectra of disordered samples, the anisotropy of the chemical shift must be eliminated in addition to the homonuclear dipole-dipole interaction. This can be achieved for abundant nuclei by combined rotation and multi-pulse spectroscopy (CRAMPS), which is the combination of homonuclear multi-pulse spectroscopy and MAS [Bur2, Ger2, Sch6]. In Fig. 3.3.13, H spectra of monoethyl fumarate are compared for different NMR techniques [Brol]. Only the combination of MAS and multi-pulse excitation produces a high-resolution spectrum of the polycrystalline powder. 

Lesage et al. have shown that the resolution of the proton NMR spectroscopy of powdered solids can be improved significantly when multi-pulse sequences are employed [44a]. In the approach based on combined rotation and multipulse spectroscopy (CRAMPS) (Figure 7.9) the problem of dipolar line broadening is usually overcome. 

Podkorytov and Skrynnikov derived analytical equations for the relaxation rate in case of the application of alternating-phase spin-lock field and demonstrated that the exchange parameters ean be determined from the dependenee of the relaxation rate on the spin-loek pulse duration. Such measurements can be used in combination with rotating-frame methods to analyse multi-site exchange. 

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