Department of Chemistry, University of Alberta         June 2002
NMR News 2002-03
News and tips for users of the Varian NMR systems in the Department

There are no fixed publishing dates for this newsletter; its appearance solely depends on whether there is a need to present information to the users of the spectrometers or not.

Other content of this NMR News is no longer meaningful and has been removed April 2010.



new utility for postscript file viewing: ghostview


printer/plotter names


gradient shimming: one possible reason for failure


New utility for postscript file viewing: ghostview
In the last issue of NMR News (2002-02) information was provided on how to create postscript files, instead of regular plots, that can be imported into graphics programs for editing. With a newly added utility, called ghostview, it is easy to view the postscript files created on a UNIX/LINUX computer before transferring them to a PC or Mac for graphical editing.

This has the big advantage of having a way to check if the result is really as desired before the transfer. All you have to do, after creating a postscript file as described earlier, is type ghostview <filename> or gv <filename> in a UNIX/LINUX Terminal. This will start the program with the specified file already open. ghostview allows rotations of the plot, zooming etc. and provides a very good impression whether the file serves the desired purpose or not. Alternatively, you can type gv or ghostview directly in VNMRJ. This will start the ghostview program but you have to load the desired file into the program.

Thanks go to Dr. Chang-Chun Ling for suggesting ghostview.

Printer/plotter names
With the possibility to create postscript files, the names of the plotters are more of a concern than before when nobody ever changed them. The following new nomenclature for plotters has been implemented:

plot to plotter

plot to postscript file





8.5 x 11 landscape

all spectrometers and data stations



8.5 x 11 portrait

Note that there are more valid plotter names but those are not for general use and will not work. The underlined name is the one chosen by the VNMRJ bootup script, i.e. without user intervention this will always be the one in use after starting VNMR.

Gradient shimming: one possible reason for failure
Gradient shimming is a very popular way to optimize the homogeneity of a spectrometer because it is easy to do and works most of the time. One reason for failure is when the sample does not have enough time to equilibrate to the temperature inside the probe. If a sample is taken out of the fridge it is substantially colder than the temperature inside the probe. The variable temperature (VT) gas flow enters the probe at the bottom and exits on top. Therefore, the sample will start to warm up at the bottom. This creates a temperature gradient in the z-direction and hence it is often the z1-shim that is adjusted wrongly by the gradient shim routine. The VT gas flow cannot be increased to speed up the equilibration as otherwise the sample starts to vibrate with disastrous results, especially in 2D experiments. The only way to solve the problem is to wait a couple of minutes and, if necessary, repeat the gradient shimming when the sample has equilibrated. This is especially true for aqueous samples (D2O or H2O). There is nothing wrong with repeating the gradient shimming. This problem occurs with all spectrometers in principle but mostly with the higher field instruments.

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