Some Brief Comments on the Source of Artifact Suppression in NMR Spectroscopy
By Paul D. Ellis, Ph.D.
The intent of this discussion is to bring clarity to some outstanding efforts to remove unwanted signals from an NMR spectrum.
There appears to be some confusion relative to the origin of artifact suppression methods by which artifacts can be removed from an NMR spectrum be it from liquid or solid samples. This confusion may be mostly amongst young investigators, who are younger than the original research. To place this comment on an age scale, the original papers were published more than 40 years ago. Let’s be clear on what is meant by an artifact. By artifacts we mean spurious signals that follow the phase of the rf. These artifacts are often described as “acoustic ringing” or “background signals”. Going back in time (too many years), Steve Patt1 (an application chemist at Varian at the time) and my own group (at the University of South Carolina) were interested in removing acoustic responses. Canet2 independently proposed a sequence which is almost identical to Patt’s. Patt’s basic idea can be summarized in four experiments:
Experiments 1 & 2 represent the usual phase cycle. That is, subtract 2 from 1 yield: 2 artifacts and 2 NMR signals. Notice the pesky artifacts are unaffected by the normal phase cycle. The genius of Patt and Canet’s experiments was the insertion of an inversion pulse at the beginning of experiments 3 and 4. When adding the difference of the results from experiments 3 and 4 to the results of experiments 1 and 2, the total gives rise to simply 4 NMR signals. To a good approximation the artifacts have been eliminated. Admittedly, this represents a linear approximation to an inherently nonlinear process. Nonetheless, this simple sequence works well.
Read the entire article A Brief Note Describing Artifact Suppression in NMR Experiments.
