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 - Ding, Luyi.; Fraser, Catharine A.; Gardner, Graeme J.; Lam, Joe.; McCooeye, Margaret.; Mester, Zoltan.; Sturgeon, Ralph E.