Evaluation of several global resolution functions for liquid chromatography

An interpretative approach, that makes use of the overlapped fraction of each chromatographic peak as elementary resolution criterion, was applied to the separation of mixtures of compounds. The elementary resolution measurements for all peaks in the chromatogram were reduced to a single numerical value using several functions: normalised by the mean resolution product, unnormalised product, geometrical mean of the unnormalised product, and worst elementary resolution value. The descriptive capability of these reduction functions was evaluated through the observation of global resolution diagrams and the change in the shape of the chromatograms in the selected factor space. MICHROM, a software program which permits the reliable simulation and optimisation of mobile phase composition, was used for this task. Among the four functions, the unnormalised product offered the best resolution measurements in agreement with the chromatographer judgement. The methodology is illustrated with three mixtures: six thiazide diuretics, three diuretics and five beta-blockers, and seven fluorescent diuretics, eluted with micellar mobile phases of sodium dodecyl sulphate without and with 1-propanol. The conclusions are equally valid for other chromatographic modes. (C) 1999 Elsevier Science B.V. All rights reserved.