Electrochemical determination of histamine derivatized with o-phthalaldehyde and 2-mercaptoethanol

High-performance liquid chromatography coupled with electrochemical detection was used to determine histamine following precolumn derivatization with o-phthalaldehyde (OPA) and 2-mercaptoethanol. The isoindole derivative which is obtained as reaction product was electrochemically active at a moderate potential (peak potential +0.4 V). Direct oxidation of histamine required a much higher potential (peak potential +1.05 V) and was of no practical use. No electrochemical signal was observed for the reaction product of histamine with OPA. Changing the pH of the mobile phase had little effect on the electrochemical response of the isoindole derivative of histamine, which was well separated from analogous derivatives of methylated histamines, mono- and polyamines and amino acids by isocratic elution from a reversed-phase column. An example of a practical application of the method to the estimation of histamine in rat brain is presented.