Methods have been developed for measuring the equilibrium binding constants (K) for lanthanide shift reagents with donor substrates. Although Infrared Spectroscopy proved useful1for determining the binding of substituted anilines to the tris-tetramethylheptanedionate of Ytterbium, it was found that NMR was more sensitive and applicable to a wider range of substrates than simple alcohols and amines2,3. The NMR procedure of progressive