Fig. 2

Representative chromatograms of plasma samples using the oxidation protocol (a) or oxidation–reduction protocol (b). Each plasma sample was pre-purified with alumina extraction and processed with high performance liquid chromatography. Plasma samples were then either oxidized using detector settings of +180 mV (a) or oxidized and then reduced using detector settings of + 300, + 150, and − 350 mV (b). DHBA dihydroxybenzylamine, DHPG 3,4-dihydroxyphenylglycol, NE norepinephrine