Chromatograms of bupropion and metabolites at the lowest limit of quantification: 0.3ng/mL for R-bupropion (A), S-bupropion (B), (2R,3R)-4-hydroxybupropion (C), (2S,3S)-4-hydroxybupropion (D); and 0.15ng/mL for erythrodihydrobupropion A (E), erythro-dihydrobupropion B (F), threo-dihydrobupropion A(G), threo-dihydrobupropion B (H), and the internal standard acetaminophen (I). The filled peak is the analyte of interest.