Abstract: By using lanthanide couple with different signs of spin expectation value z> or magnetic constant D as shift reagent, the contact shift or the dipolar shift could be canceled out and the experimentally observed NMR paramagnetic shift would contain only one of the components. The treatment assumes that the coordinating process of the substrate of lanthanide ion is in the fast exchange equilibrium and the substrate-lanthanide complex is of effective axial symmetry. The lanthanide couple technique provides an easy method to separate the individual components of lanthanide-induced shift (LIS) and to testify the validity of separation by other methods. The feasibility of this method is confirmed by application to L-ascorbic acid for the analysis of ¹³C LIS.

Key words: ¹³C NMR, Lanthanideinduced shift, L-ascorbic acid