Kinetic analysis of the fluorescence reaction of histamine with orthophthalaldehyde

Histamine reacts with orthophthalaldehyde (OPA) in an alkaline medium to form an unstable fluorescent adduct (Fbase). Acidification of the solution gives a stable adduct (Facid). In order to elucidate the mechanism of this fluorescence reaction, a kinetic study of this reaction was carried out. Although Fbase was believed to be the precursor of Facid, it was shown not to be the precursor of Facid owing to the effects of the reaction time in an alkaline medium and OPA concentration on the yields of Fbase and Facid. The kinetic analysis of the formation and degradation of Fbase revealed the pathway of the fluorescence reaction. On the basis of the results obtained in this study, the mechanism of the fluorescence reaction is proposed.