Techniques for Signal Enhancement and Discrimination in Solid-State NMR Spectroscopy

Techniques for Signal Enhancement and Discrimination in Solid-State NMR Spectroscopy 

Signal enhancement, if performed as a selective method, is very helpful for the assignment of NMR lines. In a more general manner, the application of signal enhancement techniques may improve the signal-to-noise ratio of the NMR spectrum, which is important for investigations of samples at elevated temperatures (Section II.D). 

A suitable way to enhance NMR signals of nuclei with small magnetogyric ratios or low concentrations (rare spins 5) interacting with abundant spins I is the polarization transfer from the spin I to the spin S ensemble via a cross polarization (CP) experiment. This experiment is based on a double resonance technique, which can be applied in combination with MAS for the characterization of surface sites of solid catalysts and rigidly bound surface complexes. The pulse sequence used for CP experiments is demonstrated in Fig. 4. 

The experiment starts with a 7t/2 pulse applied to the spins I. Spin polarization is transferred from the spins I to the spins S in the rotating frame during the contact pulse of the duration Tcp if the condition 

A very new approach to improve the sensitivity of NMR spectroscopy is the injection of laser-polarized Xe isotopes into the sample volume of the NMR 

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