Processing DOSY NMR Data by Chemometric Methods
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Nijmegen : [S.n.]
Number of pages
Radboud University, IMM, Analytical Chemistry, 10 januari 2006
Promotor : Buydens, L.M.C. Co-promotor : Wehrens, H.R.M.J.
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DOSY NMR can be used as a non-invasive separation method for complex mixtures. It is more and more attractive for industrial laboratories, for the main advantage DOSY NMR over routine separation methods such as LC-NMR is easy and economical implementation. With NMR instruments, DOSY NMR data can be obtained routinely but data analysis is still the main challenge to put DOSY NMR in real-world applications. A DOSY data set is obtained by measuring a series of spin echo spectra with different gradient strengths. The signals of each component attenuate with a different exponential decay rate (depending on the diffusion coefficient) as the gradient strength increases. Consequently, each channel (frequency) of the spectra is a sum of the exponential signals of the components. Traditionally, the diffusion coefficients of the components in each channel can be calculated by single channel methods, which are based on exponential fitting. In fact, the routine methods that have been implemented in commercial software from Bruker, are single channel methods. However, it has been shown that in most cases single channel methods cannot result in correct diffusion coefficients because of areas containing overlapping peaks and the influence of experimental artefacts. These disadvantages of single channel methods limit the wide use of DOSY NMR in industrial laboratories. For these reasons, multivariate methods become more and more preferable to single channel methods to analyse 2D DOSY data. Particularly, multivariate curve resolution (MCR) has proved a promising method to handle this kind of problems. It proves that MCR with good initial guesses outperforms the traditional single channel methods. The main advantages of MCR over single channel methods are that they can solve the overlap problems and result in consistent diffusion coefficient for the same component. In this thesis, the goal is to formulate general strategies to process DOSY NMR data. This can be achieved by three aspects: (1) Investigating possible improvement of MCR to process DOSY NMR data; (2) Development of preprocessing methods to improve data quality; (3) diagnosing experimental artefacts in the data to possibly optimise experimental settings.
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