DOSY Experiments - Emory University

Step-by-step description
To begin processing the gradient mapping data, first select the Process/NUG Calib panel.
Figure 2 The Process/NUG Calib panel, used for processing gradient mapping data
from the Doneshot_nugmap sequence
To process the gradient map data, do the following:
1. Click on Fourier Transform Profiles. This will perform a weighted Fourier transform of
the FID data and display the first profile. A typical set of profiles (shown stacked
vertically) obtained from the Doneshot_nugmap sequence is shown in Figure 3 below.
2. Display the first spectrum and set integral regions manually.
3. Now click the Baseline Correct All Profiles button. This will automatically baselinecorrect
all the profiles using the integral settings defined above.
4. From the Calibrant for gradient mapping drop-down menu, select either 'Pure H2O',
'1%HOD' or 'Other', depending on which sample was used to obtain the profiles. If 'Other'
was selected, enter the expected diffusion coefficient for the calibrate at the temperature
the data were recorded at.
5. Enter the (calibrated) temperature that the data were recorded at into the relevant field.
6. Check or uncheck the options 'Copy NUG coeffs to global parameters' and
'Store/update NUG coeffs in probe file' as appropriate. If this is the first time the
calibration has been done for a particular probe, it is recommended that these options be
checked.
7. Click 'Calculate NUG coefficients'. a semi-logarithmic plot of the calculated versus fitted
signal attenuation will be displayed, together with the calculated NUG coefficient.
The Calculated nugcal_ array contains the NUG coefficients calculated using the original
(uncorrected) probe file value of gcal (stored locally as gcal_). The Corrected nugcal_ array
contains the NUG coefficients calculated instead using a corrected version of gcal_
Corrected gcal_ = Original gcal_ * Correction factor
where the Correction factor is the square root of the second NUG coefficient. The corrected
gcal is stored in the probe file as parameter Probegcal_corrd (see Section 3.4). Note that any
DOSY measurements recorded after the gradient mapping has been carried out will use the
corrected value of gcal in place of the original gcal. The corrected value is the signal-weighted
average of the gradient strengths across the sample, and is generally different from that obtained
from the width of the signal profile; the latter method is relatively inaccurate and does not allow for
gradient non-uniformity corrections.
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