Electrophoretic separations of twelve phenothiazines and N-demethyl derivatives by using capillary zone electrophoresis and micellar electrokinetic chromatography with non ionic surfactant

We focused our work on the separation of phenothiazines that are important drugs used for the treatment of psychic diseases. For a better understanding of the metabolism of these solutes, we wanted to separate not only a mixture of 12 phenothiazines but also a mixture containing phenothiazines and their N-demethyl metabolites by capillary electrophoresis. Separations in capillary zone electrophoresis were performed using 3 x 10(-2) mol/L H3PO4 (pH 2.5) but the obtained resolutions were not entirely satisfactory especially with regard to phenothiazine -N-demethyl derivative pairs. To improve the obtained results, we have performed separations by using micellar electrokinetic chromatography. In this approach, we used a running electrolyte containing 3 x 10(-2) mol/L H3PO4 electrolyte (pH 2.5) and octaethylene glycol monododecyl ether (C12E8) as neutral surfactant. By introducing 2 x 10(-3) mol/L C12E8 in the electrolyte, 11 out of 12 phenothiazines have been baseline separated. With respect to the separation of a mixture containing 3 phenothiazines and their 3 demethyl derivatives, we obtained an excellent separation by using a running electrolyte prepared with 7.5 x 10(-4) mol/L C12E8 and 3 x 10(-2) mol/L H3PO4.     

Optimization of St John's Wort flavonoid separation by reversed phase liquid chromatography on a silica-based monolithic column

Summary An optimization procedure for the separation of flavonoids from St John's Wort by reversed-phase high-performance liquid chromatography on monolithic stationary phase is described. Three-component mobile phase systems are studied using experimental design methodology. The starting experimental domain is a triangle, each vertex of which is a pure component. From preliminary isocratic experiments, truncations in the domain are performed leading to a quadrilateral shape working domain with no symmetry. To cope with both separation and analysis time, desirability functions are used. Optimal conditions are finally given by binary systems and the four flavonoids are separated in less than seven minutes.     

Silica gel-based monoliths prepared by the sol-gel method: facts and figures

There is a great deal of interest in continuous beds as stationary phases for both HPLC and CEC. There are various ways to prepare monoliths, by polymerization of organic species or by polymerization of silicon alkoxides. The former method has recently been reviewed, while silica based monoliths are now commercially available. The purpose of this paper is to deal with the problems associated with silica based monoliths. The most important problem is obviously the cracking and the shrinkage of the bed during drying. The second problem is monolith cladding. Much literature has been published but no definitive solution is available and thus a wide research area remains open. Monoliths are a compromise between loadability, permeability and mass transfer kinetics. Due to the better mass transfer properties of a monolithic skeleton over distinct particles, high flow rates and high speed separations are possible.     

Polyhydrogenosiloxanes: Powerful Tools for Silanization of Commercial Monolithic Rods

An in situ method of bonding monolithic rods clad in poly-ether-ether-ketone (PEEK) based on polyhydrogenosiloxane is described. The hydrogenosiloxanes provide good solubility for the substances used in the silanization reaction in aromatic hydrocarbon solvents (non-aggressive to PEEK). The reaction of the Si-H bond with silanol groups produces hydrogen as a non-aggressive byproduct to the environment. This hydrogenosiloxane method is illustrated in the synthesis of monomeric and polymeric acceptor-bonded, monolithic phases. The use of these new bonded monolithic rods for the separation of PAHs in normal phase LC is described.     

Early steps of silica-based monolith fabrication as monitored by 29Si nuclear magnetic resonance spectroscopy

We review here the contribution of 29Si NMR to monitor the early steps of fabrication of monoliths.     

Chromatographic characterization of a bonded liquid crystal stationary phase for HPLC

Summary A chromatographic and thermodynamic study of the compound [4-(allyloxy)benzoyl]-4-methoxyphenyl (ABMP) as a model of a chemically bonded liquid crystal stationary phase for HPLC was undertaken. A number of polycyclic aromatic hydrocarbons (PAHs) and two small solutes, carvone and pulegone, were studied under varying solvent and temperature conditions. Plots of log k vs. % organic in the mobile phase were not completely linear in all cases. The van't Hoff plots revealed at least one phase transition. The enthalpies of solute transfer from the mobile phase to the ABMP phase were determined for several PAHs. All tests indicate that ABMP possess liquid crystal properties when bonded to particulate silica.     

Behavior of haloperidol and various phenothiazines on several alkyl bonded phases

Haloperidol and phenothiazines are present in psychiatrical treatments. An analysis in body fluids is tedious because of the presence of demethylated (DM) derivatives of phenothiazines. The behavior of some interfering solutes on alkyl bonded phases has been studied. Phenothiazines and DM derivatives exhibit a very similar behavior with a binary eluent (phosphate buffer-acetonitrile), which precludes an optimization with this system. When a ternary phase is used (phosphate buffer-acetonitrile-methanol), haloperidol and reduced haloperidol behave differently as compared with phenothiazines. In this mode it is possible to unambiguously detect haloperidol that would otherwise interfere. Phenothiazine peaks are characterized by a large tailing. An interesting feature is the comparison between cyclohexyl bonded and octadecyl bonded phases, the former being much more efficient.     

Some questions for chromatographers

Summary This paper is a brief survey of some problems which are not completely solved in chromatography. GC stationary phases are too numerous, Mc Reynolds data require reexamination, retention in temperature programming is not simple to predict. In LC there is a lack of a reliable model to predict the capacity factor for a wide range of solutes, retention mechanism on some phases is not fully understood, data on diffusion coefficients are scarce. SFC suffers from a lack of useful model for retention.Dedicated to Professor Leslie S. Ettre on the occasion of his 70th birthday.     

Chromatographie sur couche mince de microparticules de gel de silice

Résumé On décrit la préparation de plaques efficaces pour la chromatographie en couche mince (sans liant), utilisant les pertites particules de gel de silice à présent disponibles (5–40 m). On discute le performances obtenues et les illustre par différentes séparations de mélanges faites tant en chromatographie d'adsorption qu'en chromatographie du type partage avec phases inversées. On discute les paramètres qui contrôlent la migration du solvant et l'élargissement des bandes et montre qu'il n'y a pas une nouvelle méthode révolutionnaire de chromatographie mais le progrès normal d'une technique analytique classique, progrès prévu de longue date [1].

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Thin-layer chromatography with microparticles of silica gel

Summary The preparation of efficient thin-layer plates (binder free) made with the newly available samples of small silica gel particles (5 to 40 m) is described. The performances are discussed and illustrated by various applications to the separation of mixtures by adsorption and reversed phase partition chromatography. The parameters which control solvent migration and band broadening are discussed. It is shown that there is no such revolutionary concept as high performance thin-layer chromatography, but merely the normal advance of a conventional analytical technique following predictions made long ago (1).