13C solid-state NMR chemical shift reproducibility across spectrometers.

Precise 13C NMR chemical shifts were measured for a set of reference compounds on five solid-state NMR instruments to evaluate reproducibility across different field strengths (300-1000 MHz), MAS spinning rates and spectrometer manufacturers. Reference materials comprised five compounds included in a pan-European research program BEST-CSP dealing with bringing together experimental and theoretical approaches to investigate crystalline materials. The structures included molecular solids with pharmaceutical relevance. All instruments were standardized to a common referencing protocol using internal DSS standard. The resulting 13C isotropic shifts showed excellent agreement across instruments: variations were typically within 0.2 ppm, with the largest observed discrepancy being 0.3 ppm. Statistical analysis confirmed no significant systematic dependence on magnetic field strength or MAS rate - chemical shift values at 300 MHz and 1000 MHz were virtually identical given consistent referencing. Error analysis indicates that measured shifts are robust within tenths of ppm, reinforcing the reliability of chemical shift databases aggregated from different labs. These findings highlight that, with consistent scaling, solid-state 13C NMR chemical shifts are reproducible across diverse hardware, lending confidence to multi-instrument studies and combined chemical shift compilations.