Separation and quantitation of the stereoisomers of ephedra alkaloids in natural health products using flow injection-electrospray ionization-high field asymmetric waveform ion mobility spectrometry-mass spectrometry

A method is described for the determination of ephedrine (E) and pseudoephedrine (PE) and their metabolites norephedrine (NE), norpseudoephedrine (NPE), methylephedrine (ME), and methylpseudoephedrine (MPE) alkaloids in natural health products by flow injection-electrospray ionization-high field asymmetric waveform ion mobility spectrometry-mass spectrometry (FI-ESI-FAIMS-MS). The determination of the six alkaloids requires the separation of diastereomic pairs of E-PE, NE-NPE, and ME-MPE. FAIMS was able to resolve/separate these isomeric pairs based on their gas-phase ion mobility differences. The FAIMS-based separation and detection approach has been tested on over-the-counter diet pills. Following the extraction of the tablets, either by pressurized fluid extraction developed in-house or with sonication, the ephedra alkaloids were quantified using a modified isotope dilution approach. Detection limits for the alkaloids ranged from 0.1 to 3 ng/mL, and a linear range of at least 2 orders of magnitude was observed for the six analytes. The throughput of the current configuration of the FI-ESI-FAIMS-MS system is 2 min/sample, which is significantly higher than conventional chromatographic approaches. The developed FI-ESI-FAIMS-MS method has been compared with a conventional LC-UV analysis, and good agreement has been found for the major alkaloids.