Simultaneous NMR of both 23Na and 51V

When one looks at an NMR spectrum, it is almost always assumed that the spectrum is composed of the resonances of only one nuclide. There are examples where this is not the case. One of these examples is shown below. The spectrum is that of sodium orthovanadate, Na₃VO₄ (which also forms Na₂VO₃(OH) in aqueous solution). The spectrum contains the resonances of both ²³Na and ⁵¹V and shows the ratio between the VO₄^3- and [VO₃(OH)]^2- ions.



This spectrum was acquired on a 300 MHz spectrometer.

23Na Background in NMR Tubes.

When we measure NMR spectra, we want to observe the NMR spectrum of our sample only. However, NMR probes, tubes (or MAS rotors) must be made of real materials, so we should expect some NMR background signals for the materials present inside (or near) the coil. The user should be aware of the presence of these signals. Instrument companies expend a great deal of effort to minimize the number and intensity of background signals in their NMR probes (this is one of the reasons they are so expensive). The figure below shows three ²³Na NMR spectra taken on a high resolution NMR spectrometer. The top trace is the spectrum of an aqueous solution of NaCl, the middle trace is that of an empty NMR tube and the lower trace is that of an empty NMR probe. One can see that although the NMR probe is free of a ²³Na background signal, the NMR tube is not.