The analysis of enantiomeric and diastereoisomeric mixtures of ephedrine and pseudoephedrine using reversed-phase HPLC of nickel dithiocarbamate complexes.

Following their conversion to dithiocarbamate ligands and thence to nickel complexes, enantiomeric mixtures of ephedrine or pseudoephedrine may be separated and quantitated by reversed-phase High Performance Liquid Chromatography (HPLC) using ternary solvent mixtures. The solvent used to dissolve the complexes prior to injection was found to have a significant effect on the separation. In a similar manner, a mixture of the diastereoisomers ephedrine and pseudoephedrine was separated and quantitatively analysed using a binary solvent as the mobile phase. This separation was achieved both with prior formation of the nickel complexes and also with on-column formation using nickel(II) ions in the mobile phase. The analysis of diastereoisomeric contaminants in pharmaceutical products and raw materials containing ephedrine or pseudoephedrine is illustrated.