An HPLC method with on-line cleanup coupled to the separation column is described for determination of (-)-norephedrine, (+)-norpseudoephedrine, (-)-ephedrine, (+)-pseudoephedrine, (-)-N-methylephedrine, (+)-N-methylpseudoephedrine, and (+/-)-synephrine in finished dietary supplement products. Test portions were extracted in acidified aqueous acetone. A filtered aliquot was cleaned up on a strong cation exchange (SCX) precolumn that later was automatically coupled to the SCX analytical column. Measurement was by full-scan UV spectra for confirmation of identity by spectral matching and real-time integration of three wavelength signals for multiple quantitation. (+/-)-Synephrine was also quantitated by native fluorescence. Recovery averaged 95-100%. Determination of the major ingredients (-)-ephedrine, (+)-pseudoephedrine, and (+/-)-synephrine compared favorably to findings by an independent LC-MS analysis for a set of 25 samples. The results of a survey were reported for total ephedrine alkaloid and synephrine content and were compared to content declaration, for approximately 48 finished products.
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Niemann et al. (2003) studied this question.
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