Magnetic susceptibility measurement by NMR: 1. The temperature dependence of TMS

Usually a dedicated susceptometer is needed to measure diamagnetism accurately. An NMR spectrometer is more readily available in most chemistry departments but till now has been inaccurate for measuring diamagnetism. An improved NMR method is introduced to measure the magnetic susceptibility, or diamagnetism with similar absolute accuracy as other methods. This is achieved by accurate modelling of the NMR sample shape and response profile of the probe. The new method is validated by comparing the measured diamagnetism of water against the literature standard to within 0.05%. As a first example of its application, the diamagnetism of CDCl₃ was measured over a range of temperatures and used to reanalyze earlier measurements of the variation of the chemical shift of tetramethylsilane in CDCl₃ against ³He gas. This improved on the accuracy and reliability of the result and will allow, for the first time, accurate studies of the absolute effect of temperature on chemical shift.