Setting the scale: Efficiency of indirect referencing in solid-state NMR spectroscopy.

The use of a nucleus other than the nucleus of interest to establish the chemical shift scale (i.e., indirect referencing) in solid-state nuclear magnetic resonance (SSNMR) spectroscopy is discussed. While the technique is routinely applied in solution NMR studies, it is not applied as widely within the SSNMR community. The benefits of the indirect referencing approach in many SSNMR applications are discussed. In particular, the methods by which indirect methods improve efficiency, reproducibility and help avoid misassignments of chemical shifts are shown. Measurements via direct and indirect methods of a representative sampling of the NMR periodic table are presented to demonstrate the viability of the indirect approach. While any sample with a known chemical shift may be used for indirect referencing, adamantane is demonstrated to be a particularly well-suited solid sample.