In this paper, a novel and stable fluorescent reagent, quinoline-2,3-dicarbaldehyde (QDA), is synthesized as a probe to detect ammonium in natural water. Ammonium reacts with QDA in the presence of SO32− and Ca2+ to form a fluorescence product, which has maximum excitation and emission wavelengths at 429 nm and 518 nm. The concentration of reagents, the reaction temperature, the reaction time, and the pH in the final solution are investigated and optimized. The interferences of typical organic nitrogen and inorganic compounds are evaluated, and results prove that most volatile amines have little or negligible effect. Under the optimized conditions, this method provides a limit of detection of 0.065 μmol L−1, a calibration range of 0.216–9 μmol L−1, and reproducibility (with a relative standard deviation) of 1.9% for 1.5 μmol L−1 ammonium. For water sample analysis, the proposed method provides comparable results to those of the conventional o-phthalaldehyde method but has longer reagent stability (42 days).
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-SO 3 2- -NH 4 + , which has maximum excitation and emission wavelengths of 508 nm and 564 nm, respectively. And the possible sensing mechanism of NDA-NH 4 + 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.
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