The overall distribution for the implementation of the six executed gradients is shown in Fig. , and it is seen that Gradients 1-4 were used in most cases. Specifically, 179/315 of the cases met the criteria of Eq. ( ), requiring only six experiments. At most, 10 experiments were required, as shown in Fig. . Note that there is the possibility for any given gradient, that the criterion of Eq. ( ) might not be met, once all the if statements are evaluated. If this occurs because tR > (tG + tM + tD), manual intervention and inspection would be required to ensure that adequate experimental data for fitting could be obtained, and to possibly propose additional gradient experiments. For the present simulated dataset, this eventuality was encountered in one case. This occurred for N-butylaniline on the SB-C18 phase. This was because after removal of outliers in the isocratic data at the higher organic compositions, the NK model never predicts retention factors less than eight for this solute/stationary phase combination; the corresponding fit to the isocratic data can be seen in the supplemental material, Fig. . Alternatively, it is possible that after the final if statement for a given gradient is evaluated, that tR < (0.10tG + tM + tD). In this case, we elected to go forward with the final fitting, because while the gradient might not be ideal, Eq. ( ) is still valid. For the present dataset, this occurred for 12/630 gradients investigated at the shortest tG values. It also should be pointed out that while with this design, up to 10 experiments might be required to achieve the final design, only six experiments were used in the final fitting. One caveat to using the parameters obtained from the proposed experimental design for predicting retention behavior is to recognize that these parameters should only be used over the organic range over which the data was acquired. In the case of isocratic fits, this is straightforward; if data are fit between 20-60 % organic composition, reliable predictions should only be expected over this range of composition, and the user should be cautious of results that are extrapolated outside of this range. In the case of these gradient fits, we identified the valid range for predictions as follows min( ) max( )