An analytical method was developed for the determination of the metal deactivator additive (MDA) in jet and diesel fuels. Both uncomplexed free MDA and the copper complex (Cu-MDA) can be determined simultaneously, providing information about the copper exposure of the fuel. Using ultrahigh performance liquid chromatography, separation of MDA and Cu-MDA from the fuel matrix was attained. Two detection methods were investigated: ultraviolet absorption detection and mass spectrometric selected ion monitoring. Spectrophotometric detection was found to be a more sensitive measurement technique, attaining a lower detection limit of 0.05 ppm (mg/L) in both jet and diesel fuel.