The Model 5300 Coulochem III electrochemical detector provides simultaneous measurement of norepinephrine (NE), dopamine (DA) and serotonin (5HT) with no interference, and also measures dopamine and serotonin together in less than four minutes. The single chromatographic system provides simultaneous quantification of NE, DA and 5HT in a single sample, making more efficient use of each sample and enabling researchers to obtain information about multiple pathways in a single analysis. The system also provides a method for NE measurement.