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Phasing 2D data

Phasing 2D data


Phasing 2D data

Phasing is done differently depending on whether or not NUTS is in the Arrayed Mode.  In Arrayed Mode, the entire data set is in memory, and commands are applied to all slices simultaneously.  Arrayed Mode is available in NUTS Professional version.

Arrayed mode

Manual phasing in the first dimension can be done with either the PH or PE command.  Autophase can also be used.  This is done while viewing the first slice.  When the phase has been adjusted, exiting the phase routine applies that correction to all slices.

Phasing in the indirect dimension is a bit different, because usually any given slice has only one peak of significant intensity, so is not sufficient to determine 2 phase correction parameters.  Start by choosing a slice that has a peak with good signal-to-noise near one end of the spectrum.  

(This is most simply done by displaying an intensity plot and viewing slices in real time.  Hold down left mouse button to display a horizontal cursor, then press the right mouse button  simultaneously (or type period key on keyboard) to display slices at the cursor position).   

Once a slice is selected, exit the IP routine so that the chosen slice is displayed as a 1D spectrum.  *Place the pivot point on the large peak in this slice.*  (See PH for setting pivot point).  Now enter PH and phase this peak using only zero-order (left mouse button) correction.   Hit <Enter> to exit and apply this zero-order correction to the entire data set.

Now repeat the slice selection process, this time choosing a slice with a large peak near the opposite end of the spectrum.  Enter PH and phase using only first-order (right mouse button) correction.   Hit <Enter> to exit and apply this first-order correction to the entire data set.  Now the whole data set should be correctly phased.

"Pairwise" Arrayed mode

NUTS-Pro versions dated May 2002 and newer allow processing of phase-sensitive data such that all quadrants of data are retained, and the data can be phased in both dimensions after processing.  This is done as described above for the indirect dimension.  See details of the pairwise arrayed mode.

Non-arrayed mode

Direct dimension – The first step in processing is to import the data and process the first slice, including phase correction.  Then a macro (or link) is run that executes a series of commands on each slice, and the PS (phase same) command is used to apply this phase correction to all slices.  

To determine phase parameters in the second dimension, we need a spectrum with peaks near both ends of the spectrum.  This is usually accomplished by adding together 2 slices from opposite ends of the spectrum. To find which slices contain signal, display an intensity plot (IP), and view slices in real time (hold down left mouse button to display a horizontal cursor, then press the right mouse button simultaneously to display slices). Note slice numbers of slices with good signal-to-noise, then exit the IP routine with ENTER. Read in the first slice of interest (with SL) and place this slice into the Add/Subtract buffer (with AL). Read in the second slice. Enter the Add/Subtract routine (AS), add the 2 spectra (with plus sign) and exit the subroutine with ENTER. Now phase this spectrum, then note the phasing applied (TP). Enter the values of zero- and first-order phasing into the PA and PB parameters. Then execute this Link     ga pc sc in    to apply this phase correction.

Phasing the direct dimension after FT of both dimensions

Sometimes it is necessary or desirable to adjust phasing of the direct dimension after FT of both dimensions.  

For NUTS-Pro versions older than May 2002, (Nov 2002 for TPPI data) and for NUTS-2D versions, phasing after processing poses a problem, because NUTS discards the imaginary half of the direct dimension spectra after processing.  However, there is a procedure to accomplish this.  

Make sure the data is displayed with the direct dimension on the horizontal axis.  Use a Hilbert transform (HT) to generate a "FID" that has both real and imaginary parts.  Then use FT to recreate a spectrum that has complementary real and complex parts, and can be phased in the usual way (as described above).

Last updated: 12/8/06