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  • Author or Editor: Helena Majstorović x
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The chromatographic behavior of four mixed tris ( β -diketonato) complexes of the type [Co(acac) 3− n (phacphac) n ] ( n = 0–3), three ( β -ketoiminato)-Cu(II) complexes, two tris (alkylxanthato)-Co(III) complexes, and five bis (alkylxanthato)-Ni(II) complexes has been studied on thin layers of CN-silica gel with fifteen mobile phases, thirteen of which resulted in normal-phase systems. Linear relationships were established between the R M values of tris ( β -diketonato) complexes and the amount [% v/v ] of acetone in hexane-acetone mobile phases, and between the R M values of these complexes and the number of acac ligands substituted by phacphac ligands. The results obtained were compared with previously observed chromatographic behavior of the same substances on thin layers of silica gel and polyacrylonitrile. The corresponding separation mechanisms were also considered. It was assumed that under conditions of normal-phase chromatography with solvents of low polarity the retention behavior of complexes containing aromatic rings in the molecule is mainly determined by donor-acceptor interactions of the cyano groups of the adsorbent with the π -electron systems of the substances being separated.

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The chromatographic behavior of twelve neutral, mixed cobalt(III) complexes of the uns-cis -edda-type has been investigated in six planar chromatographic systems. Four different stationary phases - unmodified silica gel, CN-silica, cellulose, and alumina - were combined with water-organic solvent (methanol or acetone) binary mobile phases. The effect of the water content of the mobile phases on retention of the complexes was investigation systematically. On the basis of the results obtained, possible separation mechanisms were considered. Hydrophilic-interaction chromatography was assumed to be the mechanism determining separation under normal-phase conditions, i.e. use of mobile phases containing small amounts of water. Reversed-phase chromatography occurs when water-rich mobile phases are used.

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The chromatographic behavior of some phenolic compounds has been studied with the objective of understanding the role of cyano groups in the processes of chromatographic separation on thin layers of CN-silica gel. For this purpose separations were performed on thin layers of CN-silica gel, unmodified silica gel, and polyacrylonitrile adsorbent (PANS) using fourteen mobile phases, nine of which resulted in normal-phase systems. On the basis of the results obtained the effect of compound structure (i.e. properties of ortho substituents of the compounds separated) on their retention is discussed. The dependence of the order of retention of the phenols on the properties of the adsorbent was also considered. Plots of retention data ( R M against R M ) determined by use of different chromatographic systems were used to characterize the systems used. The results enabled hypotheses to be formulated about possible mechanisms involved in the separations of the phenols on these adsorbents.

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An overview of the adsorption characteristics of 3-cyanopropylsiloxane-bonded silica gel as a specific, moderately polar sorbent which can be used for separation of different classes of organic and inorganic substances in both normal- and reversed-phase chromatography is presented. The most important separation mechanisms that govern the retention on this sorbent are underlined. In addition, some recently published applications of 3-cyanopropylsiloxane-bonded silica gel as a sorbent in thin-layer chromatography are listed.

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