The chemical heterogeneity of the carboxyl groups in DOM (i.e., the range of pKa values) is reflected in the σ and n parameters of the Gaussian distribution and the modified Henderson–Hasselbalch models, respectively. A mixture of acids will approach the behavior of a single, monoprotic
Tipifarnib as σ approaches zero in the Gaussian model or as n approaches one in the modified Henderson–Hasselbalch model, and the distribution of pKa values in a mixture will broaden as σ and n increase. The σ values of BC samples (1.4–1.6) are slightly smaller than those of BU samples (1.6–1.9), and the n values of BC samples (2.2–2.5) are slightly smaller than those of BU samples (2.6–3.0). The σ of the Gaussian distribution model is the standard deviation of the distribution of pKa values, so
bud sports can be concluded that the BC samples contain a slightly less heterogeneous mixture of COOH groups than do the BU samples. Although the reasons are unknown, this is the only acid–base characteristic that distinguishes DOM samples from oil-impacted sites and pristine sites in Barataria Bay. All DOM samples from Barataria Bay contain much less complex distributions of organic acids than that which is found in SRNOM (σ = 2.2, n = 3.6, see Table 2).
