Various chiral stationary phases were investigated in sub- and supercritical fluid chromatography for the separation, without derivatization, of basic (beta-blockers, benzodiazepines) and acidic (nonsteroidal anti-inflammatory drugs, beta-agonists) pharmaca. For all racemates, baseline separation was achieved within short analysis times. For several solutes, the high resolution obtained allowed injection of milligram amounts and semipreparative collection of the enantiomers. The parameters affecting enantioselectivity (column efficiency, influence of modifiers and basic or acidic additives, and temperature) have been studied. Enantiomerization of 3-OH-benzodiazepines could be suppressed by working at low temperatures or by using acetonitrile as a comodifier. Serial coupling of different chiral stationary phase columns resulted in a column triplet (Chiralpak AD, an amylose derivative; Chiralcel OD, a cellulose derivative; and Chirex 3022, a Brush-type with pi-donor characteristics) on which all solutes investigated could be baseline separated.

SummaryThe separation of enantiomers of rather simple molecules, such as alkanes and alkanoic acid esters substituted at the 2-position, has been investigated on alkylated 0-cyclodextrin stationary phases. By observing the effect of varying the substrate and the cyclodextrin alkylating agent it has been possible to propose a mechanism for the separation.The most important factors seem to be hydrophobic interactions and the ability of the cyclodextrin to change its conformation to accept the guest molecule.

The effect of an electrochemical surface treatment on the surface microstructure of Tenax@ high-tensile-strength carbon fibres is investigated using a multi-technique approach. The fibres are treated in a laboratory set-up, which simulates the production conditions. The surface functional groups are characterized and quantified, and their dependence on the treatment intensity is determined. The surface chemistry is correlated with the fibre surface topography. It is observed that for increasing treatment intensity, the surface area does not increase significantly (except at very high intensities, in which a porous structure is formed). This contrasts with the dispersive part of the surface energy, which increases with the treatment intensity. Moreover, both basic and acidic surface functionalities are formed, the relative proportions of which change with the treatment intensity.These phenomena can be interpreted in terms of the concentration of active sites, which increases with the surface treatment and may be related to 'basal plane edges' of the (disordered) graphitic fibre microstructure.

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Abstract. Some parameters influencing the in-situ methylation by tetramethylammonium hydroxide (TMAH) during pyrolysis have been investigated with model compounds and polyaramides. Both pyrolysis temperature and excess TMAH (pH effect) influence the methylation of carboxy-, aromatic amino-, and hydroxyl-functional groups. While the solvent of TMAH, i.e., methanol or water hardly influenced the methylation of the model compounds, the solvent effect was significant for the polyaramides. This can be explained by assuming a transesterification mechanism rather than hydrolysis/methylation. N-methylation prior to the decomposition of polyaramides also may not be excluded. o 1995 John Wiley & Sons, Inc