Since early developments in the eighties of the last century, the hyphenation of separation techniques, together with Nuclear Magnetic Resonance spectroscopy, has achieved a very high level of robustness and sensitivity. The online coupling of High Performance Liquid Chromatography with NMR spectroscopy is now a routine technique in all major industrial laboratories. Used with the newer hyphenated mass spectrometry techniques such as LC-APCI (Atmospheric Pressure Chemical Ionisation) MS and ESI (Electrospray Ionisation), MS LC-NMR is an extremely powerful tool for the structure elucidation of unknown compounds within a chromatographic run. This Special Issue gives an overview of the current applications of LC-NMR in conjunction with LC-MS and other hyphenated techniques in the fields of natural product analysis, biomedical, pharmaceutical, environmental, and polymer research.
Currently, three major trends in LC-NMR applications are visible. All three strategies aim for an increase in sensitivity in NMR detection. The first is the application of a solid phase extraction (SPE) technique after the chromatographic separation to increase the peak concentration for the NMR detection. The second is the use of horizontal solenoidal micro coils which exhibit a threefold increase in sensitivity versus conventional vertical-operated double saddle Helmholtz coils. The third is the application of cryogenic coils also offering a three-fold increase in sensitivity. In addition, the SPE technique can be combined either with micro coil or cryogenic coil detection.
In this issue, the first manuscript gives an overview of the recent developments in natural product analysis, followed by a review on microseparations which discusses different applications of micro coils. The next contributions deal with the structure elucidation of bioactive compounds, the analysis of polymers and environmental degradation products. The practicability of solid phase extraction techniques in different fields is addressed in the following research papers. Critical comparisons between applications using micro and cryogenic cooled coils including SPE enrichment finally show the broad range of applications.
In the present issue only 1 H NMR detection is discussed. Future applications, however, will include LC-13 C NMR as well as parallel detected NMR spectroscopy within one probe. These subjects could be discussed further in another Special Issue of Magnetic Resonance in Chemistry.