Potential and limitations of on-line comprehensive reversed phase liquid chromatography×supercritical fluid chromatography for the separation of neutral compounds: An approach to separate an aqueous extract of bio-oil.

On-line comprehensive Reversed Phase Liquid Chromatography×Supercritical Fluid Chromatography (RPLCxSFC) was investigated for the separation of complex samples of neutral compounds. The presented approach aimed at overcoming the constraints involved by such a coupling. The search for suitable conditions (stationary phases, injection solvent, injection volume, design of interface) are discussed with a view of ensuring a good transfer of the compounds between both dimensions, thereby allowing high effective peak capacity in the second dimension. Instrumental aspects that are of prime importance in on-line 2D separations, were also tackled (dwell volume, extra column volume and detection). After extensive preliminary studies, an on-line RPLCxSFC separation of a bio-oil aqueous extract was carried out and compared to an on-line RPLCxRPLC separation of the same sample in terms of orthogonality, peak capacity and sensitivity. Both separations were achieved in 100min. For this sample and in these optimized conditions, it is shown that RPLCxSFC (with Hypercarb and Acquity BEH-2EP as stationary phases in first and second dimension respectively) can generate a slightly higher peak capacity than RPLCxRPLC (with Hypercarb and Acquity CSH phenyl-hexyl as stationary phases in first and second dimension respectively) (620 vs 560). Such a result is essentially due to the high degree of orthogonality between RPLC and SFC which may balance for lesser peak efficiency obtained with SFC as second dimension. Finally, even though current limitations in SFC instrumentation (i.e. large extra-column volume, large dwell volume, no ultra-high pressure) can be critical at the moment for on-line 2D-separations, RPLCxSFC appears to be a promising alternative to RPLCxRPLC for the separation of complex samples of neutral compounds.

Evaluation of supercritical fluid chromatography for testing of PEG adducts in pharmaceuticals.

Drug formulations containing polyethylene glycol may give rise to formation of reaction products between the aforementioned and the active pharmaceutical ingredient. Supercritical fluid chromatography has recently achieved new interest and improved instrumentation is now available. Here, supercritical fluid chromatography has been evaluated for its possible use for determination of reactions products formed between polyethylene glycol and active pharmaceutical ingredients. A mixture of polyethylene glycols with average molecular weights of 400-6000Da was separated with supercritical fluid chromatography using silica columns and carbon dioxide modified with methanol as mobile phase. Satisfactory resolution (Rs=1.2) of the individual oligomers up to a molecular weight of 1000Da was obtained using evaporative light scattering as detection technique. The active pharmaceutical ingredients, cetirizine or indomethacin were investigated in a reaction mixture containing polyethylene glycol 400 after incubation at 80°C for 120h. Polyethylene glycol esters formed upon reaction with both active pharmaceutical ingredients were observed as polymeric patterns with ultraviolet detection and identified with mass spectrometry. Cetirizine was observed to be more reactive than indomethacin. The observed difference in reactivity is due to differences in polar and steric effects between cetirizine and indomethacin. Evaporative light scattering, ultraviolet absorbance and mass spectrometric detection were investigated and each detection technique has its own advantages and disadvantages, but in order to be able to detect selected impurities in the complex mixture of impurities formed, mass spectrometry is superior.

Elucidation of an iterative process of carbon-carbon bond formation of prebiotic significance.

Laboratory experiments carried out under plausible prebiotic conditions (under conditions that might have occurred at primitive deep-sea hydrothermal vents) in water and involving constituents that occur in the vicinity of submarine hydrothermal vents (e.g., CO, H(2)S, NiS) have disclosed an iterative Ni-catalyzed pathway of C-C bond formation. This pathway leads from CO to various organic molecules that comprise, notably, thiols, alkylmono- and disulfides, carboxylic acids, and related thioesters containing up to four carbon atoms. Furthermore, similar experiments with organic compounds containing various functionalities, such as thiols, carboxylic acids, thioesters, and alcohols, gave clues to the mechanisms of this novel synthetic process in which reduced metal species, in particular Ni(0), appear to be the key catalysts. Moreover, the formation of aldehydes (and ketones) as labile intermediates via a hydroformylation-related process proved to be at the core of the chain elongation process. Since this process can potentially lead to organic compounds with any chain length, it could have played a significant role in the prebiotic formation of lipidic amphiphilic molecules such as fatty acids, potential precursors of membrane constituents.

Continuous counter-current extraction on an industrial sample using dual-flow counter-current chromatography.

Both batch and continuous separations were performed on an industrial liquor using a specially built continuous counter-current extraction centrifuge. Changing the flow regime for different batch separations showed that the elution of components from the respective ends of the coil depends on the flow rates of both upper and lower phases. It was shown that, within the scope of the study, the elution of the components was not affected by the concentration of the injected reaction liquor and more importantly that continuous processing with a counter-current chromatography centrifuge was feasible. This research represents an important step forward in making continuous counter-current chromatography (or true moving bed chromatography) accessible for the pharmaceutical industry.

Practical solvent system selection for counter-current separation of pharmaceutical compounds.

Counter-current chromatography (CCC) is a technique that shows a lot of potential for large scale purification. Its usefulness in a "research and development" pharmaceutical environment has been investigated, and the conclusions are shown in this article. The use of CCC requires the development of an appropriate solvent system (a parameter of critical importance), a process which can be tedious. This article presents a novel strategy, combining a statistical approach and fast HPLC to generate a three-dimensional partition coefficient map and rapidly predict an optimal solvent system. This screen is performed in half a day and involves 9 experiments per solvent mixture. Test separations were performed using that screen to ensure the validity of the method.