C-13 CP-MAS NMR is used as a non-destructive technique to measure the distribution of carbon types in humic substances. Although it is well-known that quantification of CP-MAS is problematic because different parts of the spectrum have different optimal contact times, a single contact time is used in most studies and in such cases C-13 CP-MAS NMR is only qualitative. Using Variable Contact Time experiments and back-extrapolating the signals for the various chemical shift regions to t=0 significantly improves quantification. Because signals decrease markedly during the beginning of an experiment, samples need a steady-state condition before acquisition of the Free Induction Decay (FID). Well-defined processing of the raw data significantly improves data quality. The effect of these various treatments on overall accuracy is shown
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