Cross-polarization quantification

Cross-Polarization Kinetics. Knowledge of the CP kinetics (dependence of the intensity of the peaks versus contact time) is essential for quantification of the CP-spectra. The CP-kinetics parameters can also provide information on the dynamic properties of the materials under study. A typical CP-kinetics curve consists of two distinct parts at short contact times the magnetization is increased followed by the decrease... 

In NMR, extensive studies have shown that solid-state CPMAS NMR spectra of most soils can be analyzed quantitatively(5,25,26) if one considers the relaxation and cross polarization lanetics of the compounds observed in the spectra. We can extend these results to imply that solid-state N CPMAS NMR spectra are also quantitative. Comparable to C CPMAS NMR, in a N CPMAS NMR experiment, quantification problems may arise from 1) incomplete relaxation of the spins during the experiment, 2) incomplete polarization transfer because of the isolation of protons from nitrogen atoms and 3) spinning side bands. The effects of these parameters on a C CPMAS NMR spectrum are extensively discussed by Wilson.(5)... 

The problem of quantification in cross-polarization has been recognized from the beginning of its application to fossil fuels,has been debated, and is still a concern in solid-state NMR. The main concerns are whether all carbons are observed equally in the CP experiment, and whether the fraction of carbons observed at true signal intensity is a faithful... 

The SPEMAS technique has the advantage to be quantitative if the recycle delay is well calibrated as a function of the spin-lattice relaxation times (TO previously measured on each signal. However, CP experiment is not much applied for quantitative aspects because the signal intensities are not only dependant of the total nuclei concentrations but also of their dynamics. In order to get quantitative reliable data fi om CPMAS data, a series of spectra have been recorded in order to exactly determine the match of optimum cross polarization, the proton decoupling power, the pulse width and the delay times. These parameter calibrations are essential before further analyses even if they take a long time. Concerning the spin-echo experiment, the low intensity of signals for few transients excluded precise parameter calibration. Anjnvay, measurements of spin-spin relaxations times (T2) is necessary for reliable quantification of spin-echo spectra. 

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