DOSY Experiments - Emory University

4.5 Processing 2D-DOSY experiments
Once DOSY data have been acquired, they need to be processed to give a 2D DOSY spectrum.
This involves the following steps:
1. Basic Fourier transformation of the raw data
2. Reference deconvolution (fiddle command) - optional, but useful if the spectrum
contains a suitable reference line which diffuses with comparable speed as the solutes in
the diffusion sample.
3. Baseline correction (fbc macro) - also optional but strongly recommended
4. Extraction of diffusion data from the spectra and synthesis of a 2D DOSY display (dosy).
Figure 15 The VNMRJ DOSY Process panel for 2D-DOSY pulse sequences.
1. After data acquisition with a DOSY experiment, a matching weighting function and zero
filling (fn) should be chosen before Fourier transforming the FID array using the
"Process all Spectra" button (executes wft command) on the DOSY Process panel
(see Figure 15). Retrieving a DOSY FID from disk usually leads to auto-processing -
Fourier transformed array data arranged horizontally (wft dssh).
2. The fiddle program (FIDDLE panel, Figure 16) allows reference deconvolution to be
used to correct the line shapes, frequencies, phases etc. of signals due to by
instrumental imperfections if a suitable reference signal is present in the spectrum
(typically a singlet). Reference deconvolution of DOSY spectra removes systematic
errors resulting from disturbance of the magnetic field and field/frequency lock caused by
gradient pulses.
Typically, set the weighting function of the ideal lineshape to a value which is minimum as
large as the widest signal in the spectrum. Select a reference line using two cursors, hit
"Select", then "Do FIDDLE". In case a TMS signal should be used for reference
deconvolution, the "FIDDLE (TMS)" button on the DOSY Process panel or the "Include
TMS satellite signals" checkbox on the FIDDLE panel should be used (required to fit the
satellites of TMS correctly).
It is recommended to save the corrected data to disk by selecting the "Write out
corrected data" option before clicking "Do FIDDLE" and use this data for further
processing (using fiddle with the 'writefid' option rewrites to the original FID file).
After loading this corrected dataset, set all the weighting parameters to 'n' to before
Fourier transforming and proceeding to the next step.
Further instructions for the use of FIDDLE are shown by the "Display FIDDLE manual"
button and more information can be found in the User Guide: Liquids NMR, and in the
Command and Parameter Reference manual.
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