Liquid Chromatographic Analysis of the Enantiomeric Impurities in Various (+)-Pseudoephedrine Samples

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Abstract
An HPLC method has been developed for the separation of four stereoisomers of ephedrine using precolumn derivatization with S( + )-l-(l-naphthyl)-ethyl isocyanate. The formed derivatives are subsequently separated on a normal-phase column and are detected at a UV wavelength of 220 nm. This method was used to quantitate the differences in the enantiomeric impurity of various samples of ( + )-pseudoephedrine. The reported method can differentiate between samples of ( + )-pseudoephedrine which differ in their enantiomeric impurity by as little as 0.02%. Possible racemization of ( + )-pseudoephedrine in aqueous solutions was also studied. Samples of ( + )-pseudoephedrine from various suppliers and, indeed, different lots from the same supplier, differed significantly in their degree of enantiomeric impurity.

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