Determination of dextro- and levomethorphan mixtures using chiral lanthanide NMR shift reagents.

Europium and praseodymium chiral NMR shift reagents were used to differentiate between dextro- and leveomethorphan. The enantiomeric shift differences (delta delta delta) demonstrated by the singlet associated with the methoxy protons were large enough to identify the levo- and dextro-isomers and to allow for the determination of as little as 10% of one enantiomer in the presence of the other in a prepared mixture. The analytical method is rapid and can analyze samples as small as 1 mg.