where α and β are compound-specific fitting parameters. However, weakly sorbing compounds (e.g., PFBA) showed slightly concave downward curves, and strongly sorbing compounds (e.g., PFDA) showed slightly concave upward curves. For such compounds, the quadratic equation (eq 3) fit the data better than eq 2. log k = a φMeOH 2 + b φMeOH + c (3) where a, b, and c are fitting parameters. All fitting parameters for eqs 2 and 3 as well as the standard deviations of the residuals are listed in Table .