Improving the double quantum filtered COSY experiment by "Moving Tube" NMR.

Most 2D NMR spectra show artifacts that become increasingly more prominent as the relaxation delay between transients is decreased. Additionally, "rushing" a 2D experiment may lead to reduced sensitivity. It is shown here how to collect a DQF-COSY spectrum in less time, without artifacts, and with improved sensitivity, by a hardware solution we call Moving Tube NMR (MT NMR): the sample volume is physically moved out of the receiver coil after each transient and replaced by a fresh aliquot that is nearer to the equilibrium magnetization M(0). MT NMR was implemented with an automated mechanism that gave accurate and reproducible vertical tube movement, and a very long 5mm outer diameter (OD) NMR tube to hold a larger sample volume. Comparison of conventional and MT NMR DQF-COSY showed increased sensitivity and far reduced artifacts in the latter. The so-called t(1)-noise in the MT spectrum was no worse than in the conventional spectrum, pointing to the excellent specifications of the long 5mm OD tube, and the good mechanical handling of the automated drive. Thus, MT NMR could improve throughput for routine 2D NMR experiments without reducing sensitivity or adding artifacts, if sufficient sample is available. MT NMR could also be useful in cases of limited solubility, or for nuclei with long T(1) relaxation times.