Selective Dephasing of OH and NH Proton Magnetization Based on 1H Chemical-Shift Anisotropy Recoupling

Coupling NMR to NOM

“…This work shows that one can very effectively obtain CH only spectra, and is superior to the method discussed above for non-crystalline samples. Also, despite a maximum efficiency of 14% a CH only spectrum of a humic acid sample could be obtained in just under 3.5 h. However, Schmidt-Rohr and Mao [46] also showed that a chemical filter could be incorporated into the pulse sequence which, in turn, allowed one to assign peaks to NCH or CCH(C,C) carbons using simple, and by far more accessible, double-resonance hardware rather than the triple resonance SPIDER NMR technique introduced shortly before by the same group [45]. In addition, the MQ-DEPT method is more quantitative as it is less prone to selective T 2 dephasing [46].…”

“…This allows one to overcome some of the peak overlap which plagues 1D NMR spectra of humic materials, but more importantly (as will be discussed in more detail in the liquid section of this work) it also allows for this dispersion to occur in a controlled manner. Solid-state 2D NMR has been sparingly applied to NOM [44,45,47,49,67]. In all cases rather broad lines are observed, however, this is much less severe in the cases where the 2D spectrum maps out carbon-proton correlations [44,45,47].…”

“…Solid-state 2D NMR has been sparingly applied to NOM [44,45,47,49,67]. In all cases rather broad lines are observed, however, this is much less severe in the cases where the 2D spectrum maps out carbon-proton correlations [44,45,47]. The carbon-proton 2D work (labeled this way as they are carbon detected experiments) has been based on the standard solid-state HETCOR principle [68,69,70], however, the pulse sequence has been elegantly modified.…”

“…The third method is known as phase adjustment of spinning sidebands (PASS) and involves separating sidebands according to their phase, simplifying the obtained spectrum [23]. The fourth, and by far the most utilized, is the CP-TOSS technique [22,23,24] and, as far as can be determined, it is the only one of the four techniques to be applied to NOM [42,44,45,46,47,51]. This cross polarization technique has been around for a long time and has been used extensively.…”

“…Subsequently, the natural logarithm of each peak's intensity is plotted against the contact time to yield a cross polarization build-up curve for each resolvable carbon species ( [36,44,45,46,47]). T CH and T 1ρ I are obtained by mathematically fitting the cross polarization to Equation 1 (where T IS =T CH in this case) or to a more complex version of this equation.…”