case of superconducting magnets, field stability and quench protection pose additional issues.
BM: Are there any alternative techiques for the analysis of components in mixtures?
Figure 2. Compounds previously unknown, identified by LC-NMR
Furthermore, the complexity of the structure of extracts from H. mantegazzianum are shown in Figure 3 illustrates the ability of to identify these components.
NH: DOSY can appear as a very useful alternative technique to LC/NMR, in that it allow a mixture of components to be separated according to their diffusion rate in the NMR tube, without the need of additional expensive chromatography equipment, solvents and LC methods to be developed. In order to be resolved, the diffusion rates must differ by 2% for fully resolved resonances, but 30% for overlapped signals. The quality of the data is very much dependent on the acquisition conditions but also the software used to process the data and is not a trivial task from our point of view.
Furthermore, obtaining good quality data from DOSY experiments appears to be a challenging problem when: • Signals of a degradation product at a level of 0.5% are likely to be overlapped by those of the parent compound which is present in much larger quantities.
• the degradation product is not much different from the parent compound in terms of molecular radius.
• Conformers having the same diffusion rate have to be separated and characterised.
BM: Is there any way to enhance the sensitivity for the detection of very low level of analytes?
Figure 3. Extracts from H. mantegazzianum
BM: How do you see the spectroscopic methods of detection advancing in, say, the next 3-5 years? What room for improvement is there still to be made in the hyphenated sequence you have used? What is holding advancement back?
NH: Magnets are now available up to 1GHz. Combined with cryoprobe, these provide exceptional sensitivity and resolution. The construction of bigger magnets will require new material to be found because the higher the field at which a magnet operates, the more complicated the stress and energy management techniques that must be used to ensure its physical integrity and the safety of those who work with it. All aspects of magnet design are affected, including the choice of materials for electrical conductors and structural components, the electrical insulation systems employed, and so on. In the
Dr Ndjoko spoke about other hyphenation techniques which will allow improved sensitivity such as SPE-NMR and CAP-NMR by allowing the analytes to be concentrated in a minimum volume of solvent [2]. Highly impressive example of the analysis of isomers of Tropane alkaloids are shown in Figures 4 and 5. Techniques such as these are becoming more widely used and offer great potential for the future.
Figure 5. Example of isomeric identification enabled by CAP-NMR
ABOUT THE AUTHOR
Following completion of his PhD at the University of Clermont-Ferrand Nicolas moved to a postdoctoral position at Glasgow University where he studied the modification of proteins during oxidative stress.
As an integral part of his research projects, he has extensively used NMR, HPLC and Mass Spectrometry to identify the structure of various biomolecules, ranging from chemicals, metabolites to peptides and proteins.
Nicolas has been working in chemiSPEC for 4 years. Beside his Laboratory Management role, he focuses on implementing new NMR and MS methods so as to help clients solve their scientific and technical problems.
REFERENCES 1.
www.chromsoc.com/features
2. Jaroszewski JW (2005) Hypehenated NMR methods in natural products research, Part 1: Direct Hyphenation, Planta Med 71(8), 691-700
ACKNOWLEDGEMENTS Figure 4. Example of CAP-NMR analysis
Thanks to Dr Karine Ndjoko Ioset from the Laboratoire of Pharmacognoxy and Phytochemistry from the University of Geneva, Switzerland
Swap’n Go
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GC/MS systems; and avoids time-consuming venting of the MS and improves laboratory productivity.
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Circle no. 38 Circle no. 39
Spectroscopy Focus
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