The compositions of the mixtures followed a modified 2IV 6-2 fractional factorial experimental design to ensure that the experiments sampled the full chemical space possible with six components, and that they systematically tested all possible non-linear interactions between the components. To illustrate how this works, Fig. shows the mole fractions (x) of each component in each mixture. (This figure is intended to illustrate the structure of the mixture matrix; SI B provides more legible tables of the mixture composition.) Cells where x ≠ 0 are highlighted in blue. If we consider the columns for TET and MDC, the first tetrad of mixtures (numbers 1 to 4) contains neither of these components, the second tetrad (5 to 8) contains TET but not MDC, the third tetrad (9 to 12) contains MDC but not TET, and the fourth tetrad (13 to 16) contains both components. Thus, the difference between the second and first tetrads indicates the effect of TET in the absence of MDC, the difference between the third and first tetrads indicates the effect of MDC in the absence of TET, and the difference between the fourth and first tetrads indicates the effect of both components together; if this latter effect equals the sum of the first two, then there is no nonlinear interaction between TET and MDC. The experimental design guarantees that this same structure of tetrads applies to all other pairs of components.