Normal Versus Inverse Coil Configurations in NMR Probes

5 Normal Versus Inverse Coil Configurations in NMR Probes 

Not counting the lock channel, an NMR probe will typically have two or possibly three RF channels. One of the channels is almost always a highband ( H and or H-only channel, whereas the remaining channel or channels will be tunable to the NMR frequency of one or more of the nuclides that fall in to the broadband frequency range to N or lower—this range includes C). 

Single-channel NMR probes were initially built to allow the observation of the NMR signal, and these probes produced fine spectra. A single-channel NMR probe for observing cannot suppress the resonance broadenings caused by J-coupling to nearby H s. The solution is addition of a second coil to allow application of a continuous stream of RF tuned to the H NMR frequency to rapidly scramble (decouple) the H s. 

If on the other hand, we wish to observe a weak proton signal from a sample, we prefer to use a probe with a receiver coil configuration in which the (or highband) coil is the coil closest to the sample. 

When modern NMR was in its infanq, few if any scientists realized that they would ever require a two-coil NMR probe in which the coil lies inside the broadband coU. It was not until the demonstration that experiment time can be drastically reduced for the acquisition of 2-D heteronuclear correlation NMR data sets by employing H detected methods and a two-coil NMR probe with the coil configurations inverted (relative to the normal coil configuration described above) that the inverse probe really caught on. Now the inverse probe (a probe with the coil closer to the sample than the broadband coil) is a staple in nearly every modern NMR laboratory. 

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