Sample shape design for a micro-volume NMR spectroscopy

The authors examined a shape of sample on micro-volume, which is a several ?L, nuclear magnetic resonance (NMR) spectroscopy in order to obtain uniformed magnetic flux density in the sample and a sharp NMR spectrum by using a conventional NMR apparatus. Firstly, they simulated the magnetic flux density distribution in spherical and cubic shaped samples and calculated NMR spectra from each shape. The simulated NMR spectra from spherical samples were sharp enough, being <0.1 ppb in a full width at half maximum (FWHM). On the other hand, the simulated NMR spectra from cubic samples were much broader than those from spherical samples. Then, they made polydimethylsiloxane sample chambers with spherical or cubic sample of several ?L in volume and they evaluated NMR spectra from those micro-volume sample chambers. As a result, they obtained a sharp NMR spectrum with FWHM of 2 ppb from the sample chamber with the spherical sample, and a broad spectrum with FWHM of 220 ppb from the sample chamber with the cubic sample. These results indicate that the spherical shape is essential to obtain a shape spectrum in micro-volume NMR spectroscopy by using a conventional NMR apparatus.