Department of Chemistry,
University of Alberta
NMR News 2004-05
News and tips for users of the NMR systems in the Department
Editor: Albin.Otter@ualberta.ca http://nmr.chem.ualberta.ca
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 May 2010.
Macro for plotting of arrays
Arrayed spectra can now be plotted in a very straightforward way by the macro plarr ("plot array"). This can be done in landscape (plotter='8x11L') or portrait (plotter='8x111P') and also includes printing in postscript mode to a file (plotter='ps8x11L' or P). The macro is interactive and asks for input on how to plot the data. plarr is available on all spectrometers and data stations.
Thanks go to Mark Miskolzie for this contribution.
The signal at 5.2 ppm is almost certainly an anomeric proton in the alpha configuration (J = 3.7 Hz). At 4.6 ppm a beta-H1 is visible too (J=8 Hz) although this one partly overlaps with a fairly intense unidentified peak. This is a very dry champagne (also fruity and well balanced according to the label!). It could be expected that a sweeter variety would produce more carbohydrate signals.
The C13 APT spectrum was recorded in only 2.5 minutes (72 scans). If run for a longer time, the smaller components also appear in the C13 spectrum, confirming for the most part their carbohydrate origin.
Needless to say that the price of champagne is not due to the water or the ethanol (nor the bubbles!) but rather due to the smaller components that provide the taste and flavor.
The removal of the bubbles might at first sight just look like a gross insult to the art of champagne making. However, something can be learned from this that goes way beyond champagne: NMR samples need to be as homogeneous as possible. That includes:
Temperature gradients are probably the least obvious problem. They result from samples measured at a different temperature than they were stored before insertion into the magnet. The warm (or cold) air flows from the bottom to the top in the probe and hence the lower part of the sample warms/cools faster than the rest. Not much can be done other than waiting a few minutes. This is particularly a problem with aqueous samples. Even going from room temperature to 27C takes a few minutes of equilibration. Not waiting long enough can result in a split field, i.e. the z1-shim gradient is off and all peaks in the spectrum appear split by typically a small separation (less than 1 Hz is not uncommon). Only time and re-shimming after reaching temperature equilibrium can solve this problem.
Any field inhomogenieties, be it from the sample itself or from poor shimming, will degrade the quality of the spectrum. Bubbles in champagne are therefore nothing else but impurities in terms of NMR (sorry, bubbles!).
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