These are my crude notes if they are helpful

Notes from Paul Bowyer talk on DOSY nnmr.

Varian Performa II gradients were stronger than the JEOL equivalent ( 0.5 Tau/cm cf 0.3 Tau/cm )

JEOL software problem is that signals of different compounds line up together giving the wrong diffusion result. ( and not separating compounds ). Overlap will show an intermediate coefficient value.

VT will affect the results as it sets up convection. If lab temperature is stable then avoid the VT. If you need to use VT then you must use a temperature compensated cc experiment.

The best quality data is imperative, apart from line shape there are other complicated reasons that compound problems eg non uniformity of gradients.

Optimise the Lock Phase as the filed lurches during the pulses  and a poor lock phase can show up as distortion on higher molecular weight peaks.

3 main parameters to changes are

Diffusion time ie del on Varian.

Delta

G = gradient strength ( to be arrayed ).

Start with the bpp_led_dosy sequence

Start with 2 values of g first 50 mT and 280 mT, use at least 8 scans ( or multiple of 8 ) for the full phase cycle. Not doing this can lead to out of phase peaks.

Use the Y data processing button to process the data

                Use options connect all

                Use Home button to rescale

Check attenution of signal and adjust diffusion delay and gradiant duration ( no more than 4 ) so that you get an attenuation of 50% in the 2 spectra of the peaks of interest.

Delta is more effective than diffusuion time at changing the attenuation. But be aware that a longer diffusion time introduces convection.

Create a new “ g “ array use the logarithmic option and a minimum of 15 points

Software

                JASON – needs licence ( affordable )

                GNAT has reference deconvolution, download the latest version

                                Open file in JEOL

                                Remove all processing steps

                                Save as JEOL generic

Reference deconvolution in GNAT using a reference signal eg TMS however would need a larger molecule for larger masses.

Diffusion measurements (DOSY) 

Diffusion measurements were conducted on a Jeol type JNM-ECZ500S NMR spectrometer operating at 11.747 Tesla and 500.16 MHz for proton resonance. The NMR is equipped with a 5 mm Inverse detection proton sensitive auto tuneable ROYALPROBE™. 

Parameter optimization was carried out using the bpp_led_dosy  pulse programme (Bipolar Pulse Pairs stimulated echo Longitudinal Eddy current Delay selected from homodecoupling, presaturation). The parameters were further optimised at an interval time of 4 milli seconds, diffusion encoding pulse width of 2 milli seconds and a large Delta of 0.1 seconds.  The Eddy current delay was 20 ms. A relaxation delay of 10 seconds was used. 

The gradient strength applied during the diffusion experiment of 32 increments ranged logarithmically  from 0.03 T/m to a maximum gradient strength of 0.3 T/m (3G/mm) at 10 Amps with 16 scans for each increment.  

Data processing was performed with the Jeol Delta™ software, version 5.3.3, which uses multivariate statistical analysis to plot the results.