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Chiral separations of related compounds within a series of potassium channel activator (KCA) analogues were compared by supercritical fluid chromatography (SFC) and high-performance liquid chromatography (HPLC) at several temperatures between 0° and 52°C. Mobile phases as close as possible in performance were selected for the two modes of analysis, and the same chiral stationary phase (CSP) was used, namely, cellulose tris(3,5-dimethylphenyl-carbamate) (Chiralcel-OD). Two of the compounds, which differed only by replacement of a benzoyl group by a n-pentanoyl group, showed quite strikingly different temperature dependencies. These indicate that one compound is above, and the other below, its isoenantioselective temperature (Tiso), at which separation of enantiomers is not possible. The thermodynamic parameters for these chiral discriminations support the conclusion that, in spite of their very similar structures, quite different chiral recognition factors operate for these two racemic mixtures.

A chiral anthrylamine derivative was prepared and adsorbed on the surface of pre-packed porous graphitic carbon, and was evaluated as a chiral stationary phase in packed-column supercritical (and sub-critical) fluid chromatography. It successfully separated the enantiomers of two commercial anti-inflammatory agents and also a series of racemic tropic acid derivatives.

Discussion sur le calcul du temps mort qui mene a des contradictions; on presente deux interpretations

Several statistical and iterative methods for the calculation of the retention indices of Kovats have been compared using retention data obtained on a wide range of columns. Using homologues ranging from C1 to C22 and the linear relationship between the logarithm of adjusted retention times and carbon numbers, it has been shown that the iterative method of Guardino et al. [J. Chromatogr., 118 (1976) 13] is of adequate accuracy in the majority of analyses. It has further been shown that while higher degree polynomial relationships between carbon numbers and the logarithm of adjusted retention times give improved accuracy, their interpretation is difficult.

An extensive study has been made of three methods of determining dead-times mathematically from retention data of n -alkanes. It has been shown that the linearization procedure suggested by Grobler and Balisz is sufficiently accurate for online data acquisition and that four alkanes are adequate to calculate accurately the dead-time provided that the retention times are not excessive.

Comparaison des indices de retention pour des alkylbenzenes (alkyl=methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl) et des alcenylbenzenes ou des phenols-1 alcenes-1 avec deux types de phase stationnaire OV1 et LB550X

The problem of accurate determination of mathematical dead-time is discussed. A comparison of the several methods of calculation is made. The effect of small changes in retention time of n-alkanes on the calculated dead-time has been examined and reasons for inaccurate dead-time estimates are suggested.

To increase the usefulness of gas chromatography, a method qf data presentation is required that removes interlaboratory variations. All such methods require the determination of the system dead time, with the most useful being the retention index system of Kovats. This paper reviews the many theoretical, experimental and mathematical methods of estimating system dead time and evaluates their usefulness, not only in the estimation of dead time, but also in the subsequent calculation of Kovats indices. Recommendations are made as to the appropriate method to be used, and the expected accuracy in retention index values is estimated.

Oligomers of ampicillin and amoxicillin were isolated by preparative chromatography on DEAE-Sephadex and purified by chromatography on Amberlite XAD-2. The purity of the oligomers was checked by thin-layer chromatography and by high-performance liquid chromatography. Proton magnetic resonance and fast atom bombardment mass spectrometry showed that ampicillin yielded mainly the dimer, trimer and tetramer, and amoxicillin the dimer, trimer and some tetramer. The corresponding penicilloates were also present. For amoxicillin an important amount of the piperazinedione was formed simultaneously.