To experimentally validate the experimental design developed using previously collected isocratic data, and new set of isocratic and gradient experiments was carried out using the ). The resulting fit parameters are shown in Table . The experiment design described in Fig. was used to generate gradient experiments as summarized in Table . For acetophenone (case 2), butyrophenone (case 3) and nortriptyline (case 3), the results from the initial two gradient experiments were acceptable (i.e., the criterion of Eq. ( ) was met). Therefore, a total of six experiments were carried out for these solutes, and the data were fit to the NK model (Eq. ( )). For 4,4'-dipyridyl (case 1), the retention time for gradient 2 (see Figure ) indicated that this compound eluted within the first 10 % of the gradient, so that the design suggested an alternative gradient, gradient 6, which begins with a weaker initial mobile phase. This gradient met the criterion of Eq. ( ), and resulted in retention times for seven gradient experiments available for fitting to Eq. ( ). For p-nitrophenol (case 1), the initial experiment for gradient 1 resulted in retention past the end of the gradient, so the design suggested an alternate gradient, gradient 3, which met the criterion of Eq. ( ), and six experimental retention times were available for fitting.