Typical chromatogram of a standard injection sample, containing DA, DOPAC, 3MT, HVA, 5HT, and 5HIAA, each at 100 nM. Separation conditions were as follows. Column: 100-μm-i.d., 7.6-cm-length capillary column packed with XTerra MS-C18 reversed-phase particles. Mobile phase: pH 4.0 aqueous buffer containing 100 mM sodium acetate, 0.15 mM disodium EDTA, and 10.0 mM SOS, mixed with 10% (v/v) acetonitrile. Flow rate: 1 μL/min. Injection volume: 500 nL.