| The core of chromatography for the separation and analysis is based on the chromatographic column, whereas the development of all kinds of high-performance liquid chromatography modes is dependent on the stationary phases. Therefore, the development and exploitation of new types of stationary phases is a never-gone research topic in the chromatographic field.The chromatographic retention behaviors of the Mg/Al oxides with various Mg/Al ratios obtained by spray dried techniques, have been investigated by linear solvation energy relationships. The results demonstrate that in comparison with the contribution of these characteristic interactions for the increase of solutes' retention on Al2O3 and the oxide of Mg/Al=0.1, the ones for the increase of solutes' retention on the oxides of Mg/Al=5,10 and MgO, include not only dipolarity/polarizability, the solute hydrogen bond donating and accepting abilities, but also the intrinsic molar volume. By analysis of the regression constants on various normal-phase (NP) and reversed-phase (RP) columns reported in the literature, a new model has been developed to correlate the solute logarithmic retention factors on Mg/Al = 5, 10 and MgO columns with the data of NP and RP columns.The changes of MgO precursors, magnesium carbonate hydrates, obtained via the precipitation of K2CO3 and Mg(NO3)2 solutions with the variation of reaction conditions, have been systemically investigated. The results indicate that at lower temperatures and lower pH values, magnesium carbonate hydrates are prone to display needlelike morphology; whereas at higher temperatures and higher pH values, the crystallites tend to assemble into sheetlike particles or the regular Mg5(CO3)4(OH)2·4H2O particles assembled by sheetlike structures. The shape evolution of spherical Mg5(CO3)4(OH)2·4H2O has also been deeply studied, and the results illustrate that the formation of spherical particles are via a complex process, in which the agglomerates (MgCO3)0.8 (Mg(OH)2)0.2·1.3H2O built by many fine grains are first produced after the "burst" mixture of K2CO3 and solutions. Then the fine grains tend to assemble into needlelike or other similar particles, and the latter will further transfer into spherical Mg5(CO3)4(OH)2·4H2O particles.On the basis of above investigation, a new method, seed-induced precipitation, has been developed for synthesis of monodisperse MgO microspheres, and the reaction parameters, such as the sequence and amount of introduction of Mg5(CO3)4(OH)2·4H2O seeds, the kinds, amount and sequence of introduction of phosphate salts, and aging time of reaction solution, have great effects on the morphologies of MgO precursors. The chromatographic properties of as-synthesized MgO microspheres have also been investigated, and the results demonstrate that in comparison with the commercial silica, as-synthesized MgO microspheres exhibit excellent properties on the separation of various basic compounds and polycyclic aromatic hydrocarbons.
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