Polysiloxan-gebundenes Permethyl-β-cyclodextrin – eine chirale stationäre Phase mit großer Anwendungsbreite in der gaschromatographischen Enantiomerentrennung

Supramolecular systems-based extraction-separation techniques coupled to mass spectrometry

The combination of supramolecular chemistry and MS has not only been fruitful in the field of gas-phase fundamental studies of host-guest complexes and supramolecular assemblies. Mass spectrometric analysis has also benefited from the ability of supramolecular systems to behave as pseudophases in which solutes partition from the bulk solvent phase. Supramolecular systems-based extraction and concentration schemes and separation techniques have been widely used in different fields of analytical chemistry and are ideally suited for coupling with MS. This review describes the present status of the application of supramolecular chemistry in mass spectrometric analysis and includes topics such as the use of coacervative liquid-liquid extraction and hemimicelle/admicelle-based SPE of organic compounds prior to chromatography and electrophoresis. It also discusses the recent advances in enantioselective analysis using CD in electrophoresis- and chromatography-MS. The potential and analytical challenges of these approaches in environmental and bioanalytical chemistry, where one can expect significant developments in the future, are outlined.

Gas chromatographic separation of saturated aliphatic hydrocarbon enantiomers on permethylated beta-cyclodextrin

Enantiomers of chiral aliphatic hydrocarbons are generally difficult to separate because they lack functional groups to be derivatized in order to generate diastereomers. The systematic and quantitative separation of a series of branched hydrocarbon enantiomers using a chiral cyclodextrin stationary phase and a cryostat-controlled gas chromatograph is described. The use of a cryogenic system allows the improvement of separations for various chiral aliphatic hydrocarbons. The molecular cyclodextrin-based mechanism of the achieved enantiomeric separations is discussed briefly. Possible applications of this analytical technique are summarized, with special emphasis on the planned enantiomeric separation experiment on a cometary nucleus.

Reactive Maillard intermediates leading to coloured products-5-hydroxymethyl- and 5-(1,2-dihydroxyethyl)-3(2H)-furanone

In the course of the Maillard reaction, labile sugar degradation products are formed that are susceptible to secondary reactions and therefore have a decisive influence on the product spectrum. Such reactive intermediates may be transformed into stable derivatives with trapping reagents, and thus be protected from further reactions. Secondary processes may also be forestalled if the primary products are removed from the reaction mixture by high-vacuum distillation. By this procedure, 5-hydroxymethyl- and 5-(1,2-dihydroxyethyl)-3(2H)-furanone have been identified directly from Maillard reaction mixtures for the first time. The activated methylene group of these 3(2H)-furanones can easily enter into condensation reactions. The coloured condensation products in turn react with primary amines to pyrrolinone derivatives, which may also contribute to the colouring observed in non-enzymatic browning.

Simultaneous assessment of the intravenous and oral disposition of the enantiomers of racemic nimodipine by chiral stationary-phase high-performance liquid chromatography and gas chromatography/mass spectroscopy combined with a stable isotope technique

An enantioselective method of high specificity and sensitivity for the determination of the enantiomers of two racemic 1,4-dihydropyridine compounds after simultaneous oral (po) and intravenous (iv) administration is reported. The method is suitable for the simultaneous administration by two different routes of a racemic drug labeled with stable isotopes and unlabeled racemate. For workup, an internal racemic standard labeled with a different number of stable isotopes is added. After separation of the enantiomers by chiral stationary-phase high-performance liquid chromatography and subsequent analysis by gas chromatography/mass spectroscopy (GC/MS) with selected ion detection, the R and S enantiomer concentrations arising from i.v. and p.o. administration can be precisely measured because of their mass difference. This method has been applied to assess the disposition of the R and S enantiomers of nimodipine and nitrendipine after simultaneous i.v. and p.o. administration. The assay is highly specific and sensitive, with a limit of quantification per enantiomer of 0.1 ng/mL after extraction of 0.5 mL of human serum samples and monitoring the M- ions in the electron capture, negative ion chemical ionization mode. The calibration curve was linear in the range 0.1-100 ng/mL. Within- and between-day precision were satisfactory (coefficient of variation, < 10%). Enantiomeric excess in the range 0-100% could be accurately determined. Comparison of the enantioselective method with the achiral method (GC/MS only) gave good agreement.