Showing papers by "Klaus Albert published in 2000"

Separation and identification of twelve catechins in tea using liquid chromatography/atmospheric pressure chemical ionization-mass spectrometry.

Abstract: A method has been developed for the direct microscale determination of 12 catechins in green and black tea infusions. The method is based on liquid chromatography/atmospheric pressure chemical ionization-mass spectrometry (LC/APCI-MS). Standard catechin mixtures and tea infusions were analyzed by LC/APCI-MS with detection of protonated molecular ions and characteristic fragment ions for each compound. The identities of eight major catechins and caffeine in tea were established based on LC retention times and simultaneously recorded mass spectra. In addition, monitoring of the catechin-specific retro Diels−Alder fragment ion at m/z 139 throughout the chromatogram provided a unique fingerprint for catechin content in the samples that led to the identification of four minor chemically modified catechin derivatives in the infusions. This report is the first to describe the comprehensive determination of all 12 reported catechins in a single analysis. The utility of LC/APCI-MS for providing routine separation ...

Application of on-line C30 RP-HPLC-NMR for the analysis of flavonoids from leaf extract of Maytenus aquifolium

Abstract: Universidade Estadual Paulista Instituto de Quimica de Araraquara, CP 355, 14801-970, Araraquara, SP

Application of HPLC-NMR coupling using C30 phase in the separation and identification of flavonoids of taxonomic relevance

Abstract: The on-line separation and identification of two important taxonomic markers for plant species of the Paepalanthus genus, the flavonoids 6-methoxykaempferol-3-O-β-D-glucopyranoside and 6-methoxykaempferol-3-O-β-D-6″(p-coumaroyl)glucopyranoside, has been performed with an HPLC-NMR coupling using C30 phase 1D spectra have been recorded in the stopped-flow mode for the two predominant chromatographic peaks This is the first application of HPLC-NMR coupling using C30 phase to a taxonomic problem The technique drastically reduces the required amount of sampling for structure determination

Structure Identification of Aporphine Alkaloids by On‐Line Coupling of HPLC‐NMR with Loop Storage

Abstract: The potential of coupling HPLC separation methodology to on-line high resolution nuclear magnetic resonance (NMR) spectroscopy has been demonstrated with a mixture of nine aporphine alkaloids. A loop storage procedure after separation has facilitated the identification of closely eluted peaks (α = k2/k1 = 1.01 and Δv = 0.37 min = 367 μL). These were collected off-line and identified by a 1D 1H NMR spectrum. For this purpose an automated procedure has been implemented which includes the use of shaped pulses, multiple solvents suppression and 13C satellite suppression of acetonitrile.

Identification of trifluoperazine metabolites using HPLC–NMR of test mixtures

Abstract: The metabolites of the antipsychotic drug trifluoperazine (TFP) were investigated with on-line coupling of high-performance liquid chromatography (HPLC) and NMR spectroscopy. A chromatographic method was developed using a reversed-phase C30 silica gel column. Rats were given a cumulative dose of 90 mg kg−1 TFP dihydrochloride and samples of brain and muscle tissues were extracted after 29 h. The peaks obtained on chromatographic separation were assigned to trifluoperazine and its metabolites. With the help of chromatograms obtained from test mixtures, 1D and 2D HPLC–NMR were used to identify the peaks found for these mixtures. Copyright © 2000 John Wiley & Sons, Ltd.

Application of immobilized free radicals in supercritical fluid chromatography hyphenated with proton nuclear magnetic resonance spectroscopy

Abstract: Immobilized free radicals were synthesized and used to shorten the spin–lattice relaxation times of analytes in the hyphenation of supercritical fluid chromatography (SFC) with proton high‐field nuclear magnetic resonance spectroscopy (NMR). The effect of the immobilized free radicals was studied for the first time under on‐line SFC–NMR coupling conditions. With this method it was possible to obtain integratable NMR spectra in on‐line continuous‐flow SFC–1H NMR spectroscopy. Copyright © 2000 John Wiley & Sons, Ltd.

Application of High-Resolution-Magic-Angle-Spinning (HR-MAS) NMR Spectroscopy to Cosmetic Emulsions

Abstract: HR-MAS NMR spectroscopy was utilized for the characterization of three cosmetic emul­sions. The emulsions had the same chemical composition and were prepared in the same way except the homogenization step. Magic angle spinning (M A S) of the emulsions was applied to improve signal resolution by eliminating susceptibility changes as well as residual dipolar interactions within the sample. Spin-lattice relaxation times (T₁) were determined according to the inversion recovery technique in the temperature range of -10 °C to 40 °C to find out phase changes of the sample ingredients. ¹H and ¹³C NMR signals of the individual components were assigned by use of different 1D and 2D NMR experiments. The HR-MAS NMR technique offers many possibilities to further investigate samples between the liquid and the solid state.

Contribution of trifluoperazine metabolites to the in vivo 19F NMR spectrum of rat brain

Abstract: Fluorine-19 NMR spectra were acquired from extracts of tissues from heads of rats given the antipsychotic drug trifluoperazine (TFP). Contributions to the in vivo 19F spectra from tissues other than brain were negligible. The in vivo 19F resonance at -62.3 ppm from CCl3F consisted of 6–8 resolved resonances in vitro. Some in vitro resonances were assigned to previously identified TFP metabolites. Multiple resonances in vitro partially explain the relatively large line width seen in vivo for TFP. Unidentified metabolites were observed at about -74 to -75 ppm in a number of spectra of extracts of brain and muscle. Magn Reson Med 43:756–759, 2000. © 2000 Wiley-Liss, Inc.