Artifacts can emerge in spectra recorded with even the simplest of pulse schemes: an HMQC case study

With the development of sophisticated pulsed field gradient- and phase cycling-approaches for suppressing certain coherence transfer pathways and selecting for others it is sometimes easy to forget that the process is not flawless. In some cases artifacts can emerge because unwanted transfers are immune to the phase cycle or the application of gradients. We consider here a simple ¹H,¹³C HMQC pulse scheme and show that imperfections in the single ¹H 180° refocusing pulse can give rise to small artifacts in methyl spectra that cannot be eliminated through extensive phase cycling or the use of gradients, but that are easily removed when the pulse is of the composite variety.