GC-MS determination of l-ephedrine and d-pseudoephedrine in human plasma

To determine l-ephedrine (E) and d-pseudoephedrine (PE) concentrations in human plasma simultaneously, we used a selected-ion monitoring method with gas chromatography-mass spectrometry (GC-MS) using deuterium-labeled E and PE as internal standards. The E and PE in human plasma were extracted with hexane-ethylacetate (9/1) under alkaline conditions and were easily converted into their heptafluorobutyryl derivatives by treating with heptafluorobutyrylimidazole. The calibration curves of E and PE showed a good linearity in the range from 0.82 to 81.9 ng/ml for E, and from 0.41 to 41.0 ng/ml for PE, respectively. The limit of detection was 0.82 ng/ml for E and 0.41 ng/ml for PE in human plasma, respectively.