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Fig. 4. (A) Data from (Simpson et al., 2004) displaying the decline in 1H T1 values of 1-naphthol with increasing concentration of soil humic acid (HA). The measurements indicate that all protons are equally interacting and hence, a specific interaction between individual nuclei (1H in this example) and the HA is not observed, suggesting a strong interaction with all protons in the molecule with HA. (B) The aromatic region from the 1H spectrum does not reveal a change in chemical shift, suggesting that this is a strictly noncovalent interaction. The increased line broadening with the addition of 50 mg C L–1 of HA is indicative of a strong, noncovalent association. Reprinted with permission from Simpson et al. (2004). Copyright (2004) Environmental Toxicology and Chemistry, Alliance Communications Group.
