Variations on the chemical shift of TMS

The chemical shift of TMS is commonly assumed to be zero. However, it varies by over 1 ppm for H-1 and 4ppm for C-13 and shows a correlation with the physical properties of the solvent. Using the commonly accepted convention that TMS always resonates at zero leads to significant errors when comparing chemical shifts in different solvents. A new method for measuring absolute chemical shift with a conventional NMR spectrometer is demonstrated. The observed chemical shift is corrected by measuring and correcting for susceptibility and shape factor. Practical suggestions are made for modifying the current chemical shift standard while maintaining compatibility with earlier literature. (C) 2003 Elsevier Science (USA). All rights reserved.