Computerized optimization of RP-HPLC separation with nonaqueous or partially aqueous mobile phases

''Osiris'' optimization software was used for optimizing separations with nonaqueous or partially aqueous mobile phases, consisting of 2, 3 or 4 solvents. For nonaqueous eluents used in Nonaqueous Reversed Phase Liquid Chromatography (NARP-LC), classical transfer rules cannot be used to determine isoeluent mobile phase compositions that are generally the starting point of most of the optimization procedures. The ability of this software to determine isoeluent compositions under NARP conditions is demonstrated. This determination is performed by modeling the solute retention from different sets of two gradient runs, each set being carried out for each binary mobile phase studied. The application of retention models to nonaqueous mobile phases is discussed in terms of the accuracy of the predicted retention times. In addition, it is shown that these sets of gradient runs allow selection of the best composition space for the optimum composition search without requiring additional runs. It is demonstrated that such a selection procedure greatly reduces the number of preliminary experiments.