Single-peak resolution criteria for optimization of mobile phase composition in liquid chromatography

Three criteria that evaluate the single peak resolution (peak purity) in ch romatography, the free height fraction, free area fraction, and valley rati o, are examined. The main advantages of these criteria against other criter ia based on peak pair separation, are that the measurements are not affecte d by the identity of neighboring peaks and are normalized, which make them very intuitive. The methodology is illustrated through the isocratic separa tion of mixtures of several sulphonamides (sulphacetamide, sulphadiazine, s ulphadimethoxine, sulphaguanidine, sulphamerazine, sulphamethazine, sulpham ethoxazole, sulphamethizole, sulphamonomethoxine, sulphanilamide, sulphapyr idine, sulphaquinoxaline, and sulphathiazole). Among the three proposed criteria, the measurement of free area fractions g ave the best description of the resolution, independent of the overlapping degree of the chromatographic peaks. The usefulness of this criterion for t he resolution of individual peaks in a complex mixture is shown. The best s eparation conditions are reached easily for the individual compounds, and t ake into account peak shape and size.