Optimum concentration of ortho-phthaldialdehyde for the fluorometric measurement of serotonin

When reacted at 100°C with ortho-phthaldialdehyde (OPT), the native fluorescence of serotonin is greatly increased. For maximal serotonin fluorescence a reaction time of 5–10 min, using 0.5 g% (w/v) OPT, appears optimal over the concentration range 10–3000 ng serotonin per ml. Using these parameters, maximum separation is achieved between serotonin and blank fluorescence, and detection sensitivity and precision are highest: 1.3 ± 0.0 ng/ml and 0.38 ±0.0 ng per fluorescence intensity unit (n = 10), respectively.