Introduction

In many Relds of chemistry, biology, pharmacy and medicine, progress is often limited by the ability to resolve complex analytical problems. To this end analytical techniques have been developed in recent decades dealing with an integrated approach to the separation of mixtures together with structural elucidation of unknown compounds. High performance liquid chromatography (HPLC), gel permeation chromatography (GPC) and supercritical fluid chromatography (SFC), as well as the capillary separation techniques capillary HPLC (CHPLC), capillary electrophoresis (CE) and capillary electrochromato-graphy (CEC) are the most powerful techniques within the group of chromatographic separation methods. Nuclear magnetic resonance (NMR) spectroscopy, in particular, is useful because of its powerful stereochemical information content but it has the disadvantage of lower sensitivity in comparison to other methods, e.g. mass spectrometry (MS).

The combination of chromatographic separation techniques with NMR spectroscopy is one of the most powerful and time-saving methods for the separation and structural elucidation of unknown compounds and mixtures. Especially for the structure elucidation of light- and oxygen-sensitive substances, for example, hop bitter acids and carotenoid stereoisomers, online liquid chromatography (LC)-NMR has important advantages. Here, structure elucidation with LC-MS is not possible, because the carotenoid isomers exhibit the same fragmentation pattern. Using a classical method with offline separation, enrichment and transfer to a NMR sample tube, the isolated substances would be isomerized. A closed-loop LC-NMR flow-through system solves this problem. Online LC-NMR also allows the continuous registration of time changes as they appear in the chromatographic run. Unequivocal structural assignment of unknown chromatographic peaks is possible by two-dimensional stopped-flow LC-NMR experiments.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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