On-line coupling of capillary electrochromatography, capillary electrophoresis, and capillary HPLC with nuclear magnetic resonance spectroscopy

A novel capillary NMR coupling configuration, which offers the possibility of combining capillary zone electrophoresis (CZE), capillary HPLC (CHPLC), and for the first time capillary electrochromatography (CEC) with nuclear magnetic resonance (NMR), has been developed. The hyphenated technique has a great potential for the analysis of chemical, pharmaceutical, biological, and environmental samples. The versatile system allows facile changes between these three different separation methods. A special NMR capillary containing an enlarged detection cell suitable for on-line NMR detection and measurements under high voltage has been designed. The acquisition of 1D and 2D NMR spectra in stopped-flow experiments is also possible. CHPLC NMR has been performed with samples of hop bitter acids. The identification and structure elucidation of humulones and isohumulones by on-line and stopped-flow spectra has been demonstrated. The suitability of the configuration for electrophoretic methods has been investigated by the application of CZE and CEC NMR to model systems.