Determination of ammonium in natural water using a quinoline-based o-dialdehyde fluorescent reagent with visible excitation wavelength

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).