The focus of our research is the development and application of novel methods in liquids NMR spectroscopy. NMR is most commonly applied to relatively pure substances in solution, where it is unparalleled as a technique for extracting structural, chemical and physical information. The analysis of mixtures ,a large part of our work, is a particularly challenging area because it is often difficult to tell which NMR signals come from which molecular species. The most important current method for analysis of intact mixtures by NMR is diffusion-ordered spectroscopy (DOSY), where signals from different molecular species are differentiated by their diffusion behaviour (i.e. molecular size). When NMR signals are well separated, analysis of DOSY data is relatively straightforward, but when signals overlap (as is common) analysis is much more difficult. We are developing methods to deal with such overlapping data. The effects of overlap can be attacked both from the signal processing end and from the spectroscopy end of the problem; both these approaches form part of our current research. From the spectroscopy end, a reduction in overlap can be achieved either by reducing spectral complexity, as in pure shift DOSY, or by increasing the number of spectroscopic dimensions, as in the variety of 3D DOSY methods we have developed. From the signal processing end, covariance of the experimental data (e.g. the fact that all the signals from a particular species should show the same diffusion properties) can be taken advantage of by using multivariate methods for analysis. We are also looking at combining DOSY with other types of experiment to increase the resolving power in the diffusion dimension, as well as properties other than diffusion that may allow the signals from different chemical species to be separated.
Further information may be found at: personalpages.manchester.ac.uk/staff/mathias.nilsson/