Ammonium determination by merging-zone flow injection analysis and a naphthalene-based fluorescent probe

This paper discusses the first-time study of a naphthalene-based fluorescent probe—naphthalene-2,3-dicarboxaldehyde (NDA), in combination with merging-zone flow injection analysis for the automated fluorescence determination of ammonium. The determination was contingent on detecting the fluorescent product of NDA-SO32--NH4+, which has maximum excitation and emission wavelengths of 508 nm and 564 nm, respectively. And the possible sensing mechanism of NDA-NH4+ was proposed. The effects of the reaction parameters, including reagent concentrations, reaction flow rate, coil length, reaction temperature, and pH were optimized. Under optimal conditions, this method afforded a sampling rate of 8 h−1, a limit of detection of 0.045 μmol L−1, and RSD of 3.68% (n = 14) with 1.50 μmol L−1 ammonium, and the calibration range was 0.045–6.00 μmol L−1. Examination of the organic nitrogen interference confirmed that the method attracts minimal interference from organic nitrogen, and the stability of the NDA reagent facilitates its field application. Other exhibited advantages include low reagent consumption and high automation; the method has been utilized in the successful determination of ammonium in freshwater and rainwater. The development of NDA applications for ammonium determination also provides more options for fluorometric determination of ammonium.