As K H and n are constants at equilibrium, Eq.5 takes the form of a linear equation: y = Ax + B, where the slope A = 2n represents twice the extractant to the acid stoichiometry. The linear fit data is presented in the Supplementary Information, Figure , with average R 2 values of 0.83, 0.78, 0.92, and 0.98 for TODGA, TEHDGA, TBP, and DM-DOHEMA, respectively. While these values indicate reasonably strong correlations, the bilinear fittings provide an improved representation of the data, with each segment of the bilinear fit exhibiting equal or higher R 2 values (Table ??). The bilinear fitting is shown in Fig. , where two distinct linear regimes are observed. The regimes are summarized in Table where a comparison of the slopes are made. As observed in Table , within the first linear regime for 0.2 M TEHDGA and 1.0 M TBP, c.a. 0.5 HNO 3 molecules are associated with each extractant in the organic phase, while for 0.1 M TODGA and 0.65 M DMDOHEMA the stoichiometric coefficient is nearly 1. In the second linear regime, the stoichiometric ratio of acid:extractant increases 2 -4 times, with the largest increase being observed for the diglycolamides TODGA and TEHDGA. Prior investigations of amide extractants have noted an increase in acid concentration once a critical aqueous acid concentration is reached, and this has been correlated with an increase in aggregate size. This observation matches the description of the CMC, a critical value after which the self-aggregation of extractant molecules is greatly enhanced to form a stable distribution of reverse micelle or reverse micelle like aggregates. Similarly, for diglycolamides extractants there have been reported increases in the stoichiometric ratios of water to extractant once a critical acid concentration is reached, presumably due to hydrogen bonding between extracted water and acid. The acid concentration at which the CMC is observed is hereafter labelled the "critical acid concentration"