An optrode membrane for the determination of picric acid based on fluorescence energy transfer between fluoranthene (donor) and fluorescein octadecyl ester (acceptor) was developed. When fluoranthene is excited at 362.2 nm, it emits light in a spectral region that overlaps significantly with the fluorescence excitation spectrum of fluorescein octadecyl ester. Consequently, non-radiative energy transfer occurs from fluoranthene (donor) to fluorescein octadecyl ester (acceptor). The fluorescence of fluoranthene is strongly quenched by picric acid, but that of fluorescein octadecyl ester is not. When the optrode membrane containing these two fluorophores contacts a solution of pick acid, the extent of fluorescence quenching is increased with a threefold increase in the
Stern-Volmer quenching constant compared with the quenching of fluoranthene. This phenomenon is mainly due to the fluorescence quenching of the donor-acceptor pair by picric acid. Under the optimum conditions, the linear measuring range of picric acid is from 5.0 x lop7 to 8.0 x lop4 M. The described optrode membrane offer a more sensitive method for the determination of picric acid than the existing picric acid optrode membrane.