Hi, I'm looking for help to process a DOSY NMR spectrum. I'd like to know how to transform the gradient decay plot for a given region of the spectrum into a plot showing the diffusion constants (x-axis) vs the intensity (y-axis), sort of a distribution of diffusion constants. I've read about it online, and this website Diffusion NMR suggests applying an inverse laplace transform to a gaussian fitting function for the gradient decay plot, but I'm not sure how to do this. I was hoping someone could show me the steps to obtain this plot.
Thank you for your time.
As with most NMR data, the transformation is usually accomplished either within the software provided by the spectrometer vendor or by third-party software such as MNova from Mestrelab. I also think that these vendors use some proprietary routines for getting a good 2D plot (for example, minimizing the "streaking" one encounters when two peaks are close in chemical shift but have different diffusion constants).
Is there a particular reason you want to do this manually? Do you have access to vendor-supplied software?
Thanks. - Josh
Thanks for answering. I have access to the Bruker topspin student version. I'm studying polymer behaviour in solution, in this case a polysaccharide in water. I've managed to obtain the DOSY 2D plot relating the chemical shift (i.e. the peaks) and their diffusion coeffcients, but what I want is to plot the diffusion coefficient vs intensity for a specific peak, thus obtaining some sort of distribution of diffusion coeffcients.
Thanks for your time.
Ah. This analysis is fairly sophisticated. The distribution of diffusion coefficients for a given resonance is related to the "linewidth" of its DOSY peak in the indirect/diffusion dimension. (A narrow distribution, i.e. a single species would result in a sharp DOSY peak, but a broad range of MW's would give rise to a broad DOSY peak in the D dimension).
A quick search for "dosy measurement of polydispersity" yields this article, which you may find handy:
Without trying to go into the nitty gritty detail of your processing, perhaps you should investigate whether the tools you need are part of the DOSY Toolbox, a free DOSY analysis package produced by the Nilsson lab at the University of Manchester:
The description on that page indicates their software handles multi exponential decays, so it may be able to handle what you seek.
I'm a firm believer in using software that other people have written to solve problems that many people face - no sense in rewriting software every time a question needs answering.
Good luck! - Josh