Dual fluorescence at ca. 447 nm and 545 nm was observed from the aqueous 1-naphthylamine (NA) solutions at pH higher than 13.6. Similar dual fluorescence was also found with sodium 1-naphthylaminoacetate(NAA), but not with N, N-disubstituted 1-aminonaphthalenes such as sodium 1-naphthylaminodiacetate (NADA) and 1-dimethylaminonaphthalene (DMAN). No change in absorption spectra of NA and NAA was observed in this pH region. It was proposed that the dual fluorescence observed with NA and NAA was due to the excited state dissociation of the primary and secondary amines at high pH. From the dual fluorescence intensity ratio pH titration curve, the pK(a)(.)'s of NA and NAA were estimated to be between 14 and 15 which are much lower than the ground state pK(a). The novel approach is such a simple, convenient and frequent analysis technique that it can be widely used in detecting the substitutional derivatives of aminonaphthalene
