Interpretive optimisation strategy applied to the isocratic separation of phenols by reversed-phase liquid chromatography with acetonitrile-water andmethanol-water mobile phases

An optimisation protocol is presented for the resolution of complex mixture s in isocratic RPLC with binary mobile phases of organic solvent and water, which is based on the prediction of peak position and shape of the individ ual compounds. A good description of the retention was achieved through the application of statistical weights to the widely used linear or quadratic relationships between the logarithm of the retention factor (log k) and the organic solvent concentration in the mobile phase. The maximisation of the product of peak purities for each compound is shown as a competitive resol ution strategy versus the worst value of a selectivity parameter. Peak puri ties allow one to associate a single resolution value to each compound, whi ch is not affected by the identity of the interfering peaks. It is shown ho w when full resolution is not achieved with a single mobile phase, the same experimental data set (retention factors, asymmetries and efficiencies) ca n be used for finding two or three optimal complementary mobile phases (CMP s). Each CMP resolves fully some compounds in the mixture, while the remain ing compounds can overlap among them. The elementary limiting resolutions, which measure the maximal separation degree for each compound, are also giv en as a useful guide in the selection of the elution conditions. A mixture of 13 phenols (phenol, chloro-, bromo-, nitro- and methyl-derivatives), elu ted with acetonitrile-water or methanol-water mobile phases, is used to sho w the proposed methodology. (C) 2000 Elsevier Science B.V. All rights reser ved.