OPTIMIZATION OF A MULTISOLVENT COMPOSITION IN RPHPLC - GENERALIZATION TO NONIDEAL PEAKS

When samples contain solutes at very different concentrations, the use of the classical resolution function to express the quality of the separation does not provide a true measure of peak overlap and is therefore unsuitable for optimization. Apart from this case, the validity of the optimum is highly dependent on the accuracy of the predicted retention surfaces and it is essential to restrict the parameter space in which optimum performance is sought. As a result, most interpretive optimization procedures become unreliable for optimizing the composition of multisolvent systems in RPHPLC, particularly for non-ideal peaks. These difficulties can be overcome by the method proposed here: the ability, by means of a criterion, called GRIT, to select a restricted range of composition in order to enhance the accuracy of the response surface is developed for non-ideal peaks. The best composition within this selected range is then determined by using a modified resolution function. The performance of this procedure is discussed with some illustrative examples.