OPTIMIZATION OF SOLVENT SELECTIVITY FOR THE CHROMATOGRAPHIC-SEPARATION OF FAT-SOLUBLE VITAMINS USING A MIXTURE-DESIGN STATISTICAL TECHNIQUE

A systematic approach, using a mixture-design statistical technique, h as been developed for selecting the optimum mobile phase for the separ ation of fat-soluble vitamins in reversed-phase high-performance liqui d chromatography. A quaternary mixture of methanol, acetonitrile, tetr ahydrofuran and water was used as mobile phase. Retention time and pea k width were recorded in ten runs augmented with five replicates and t he data were subsequently fitted to special cubic polynomial models. T he resulting mathematical equations enabled prediction of resolution o ver the entire parameter space. Contour plots of minimum effective res olution and maximum retention time as a function of mobile phase compo sition are presented and discussed. Visual inspection of these plots p rovides an overview of the quality of the separation and the analysis time required for each possible mobile-phase composition within the pa rameter space. It is demonstrated that the methodology followed was an important tool which enabled the taking of informed decisions necessa ry for selection of the optimum mobile phase for a chromatographic sep aration. A combination of R-S minimum and t(R) maximum as optimization criteria in a multicriteria decision-making plot using pareto-optimal ity concept is discussed. This combination enabled visual demonstratio n of the compromise between separation quality and the economics of an alysis time. Our methodology has been compared with the common used te chnique of overlapping resolution mapping'.