Structural analysis of geochemical samples by solid-state nuclear magnetic resonance spectrometry. Role of paramagnetic material

Characterization of allophanic Andisols by solid-state 13C, 27Al, and 29Si NMR and by C stable isotopic ratio, δ13C

“…The reduced sensitivity could be due to the presence of paramagnetic materials in these samples, which accelerate the relaxation of the magnetization and reduce the relaxation time (T 2 ) thus resulting in line-broadening. Reduction treatment by dithionite alleviates this shortcoming (Vassallo et al, 1987), but we persevered here with non-destructive characterization by NMR.…”

Determination of T1ρH Relaxation Rates in Charred and Uncharred Wood and Consequences for NMR Quantitation

“…Clearly, finding an apparently linear relationship between ln(intensity) and contact time [2,3,29,32,33,44,45,49,50,56] is not sufficient to guarantee that an accurate T 1r H value can be determined. Fitting an exponential decay function to the decay phase of VCT data [16,52], essentially an equivalent procedure, suffers from the same problem when slowly cross-polarizing nuclei are present. The VCT experiment will only give accurate T 1r H values when the absence of slowly cross-polarizing nuclei can be assured [46].…”

The removal of magnetic materials from surface soils - a solid state 13C CP/MAS NMR study

“…In the past, the problems posed by paramagnetics in the solid state have been addressed by the removal of ~e("') with either dithionite in the case of soil samples and clay fractions (Vassallo et al 1987;Skjemstad et al 1992;Preston et a1 1994) or HF in the case of soil clay and humic fractions (Calderoni and Schnitzer 1984;Skjemstad and Dalal 1987;Preston et al 1989). Arshad et al (1988) also tested chemical reduction using dithionite and stannous chloride for improving spectral resolution and sensitivity but with limited success.…”