A Novel Analytical Method for Trace Ammonium in Freshwater and Seawater Using 4-Methoxyphthalaldehyde as Fluorescent Reagent

Abstract

A novel fluorescent reagent for determination of ammonium, 4-methoxyphthalaldehyde (MOPA), was successfully synthesized in this study. Under alkaline conditions, MOPA could reacted with ammonium rapidly at room temperature, producing fluorescent substance which had maximum excitation at 370 nm and emission wavelength at 454 nm. Based on this, a novel fluorescence analysis method was established for the determination of trace ammonium in natural water. Experimental parameters including reagent concentration, pH, reaction equilibrium time, and metal ions masking agent were optimized. The results showed that the optimized MOPA concentration was 0.12 g/L, pH was in the range of 11.2–12.0, and sulfite concentration was 0.051 g/L, respectively. Metal ions masking agent had no obvious effect on the fluorescence signal. With the reaction time of 15 minutes, linear range of this method was between 0.025 and 0.300 μmol/L, and the method detecting limit was 0.0058 μmol/L. The matrix recovery of the proposed method was in the range of 93.6–108.1%. Compared with the OPA method, this method was much more sensitive and rapid without the interference of background peak and would be more suitable for developing a portable fluorescence detection system.

Fluorescence-Enhanced Tb-MOF for Highly Sensitive and Selective Detection of Ammonia Nitrogen in Groundwater

“…Sulfite is necessary for ammonia nitrogen detection due to its indispensable effect on the formation of the isoindole complex between dialdehyde and ammonia nitrogen. 24 Thus, the optimal sulfite concentration was then studied. As shown in Figure S4C, the fluorescence intensity changes most when the Na 2 SO 3 concentration is 5.157 × 10 −4 M, indicating the concentration is most suitable for ammonia nitrogen detection, and the following sensing experiments were conducted at the optimal sulfite concentration.…”

“…The effect of different concentrations of a sodium sulfite solution on the determination of ammonia nitrogen by the OPA-Tb-MOF was studied by a molecular fluorescence spectrometer. Sulfite is necessary for ammonia nitrogen detection due to its indispensable effect on the formation of the isoindole complex between dialdehyde and ammonia nitrogen . Thus, the optimal sulfite concentration was then studied.…”

“…Zhang et al prepared an ammonia detection sensor called M 2 OPA with a detection limit of 3.5 nM . Liang et al prepared MOPA for detecting ammonia nitrogen with a detection limit of 0.0058 μM . However, the drawbacks of a long reaction time, a small detection range, and poor repeatability make it difficult to achieve fast and accurate detection in practical applications.…”

“…23 Liang et al prepared MOPA for detecting ammonia nitrogen with a detection limit of 0.0058 μM. 24 However, the drawbacks of a long reaction time, a small detection range, and poor repeatability make it difficult to achieve fast and accurate detection in practical applications. Moreover, the existing fluorescence detection method mainly involves quenching, which is easily affected by the environment.…”

An Electrochemical Enzyme Biosensor for Ammonium Detection in Aquaculture Using Screen-Printed Electrode Modified by Gold Nanoparticle/Polymethylene Blue

“…Calcium ion, magnesium ion, sulfide and turbidity will interfere with the determination. For the fluorescence detection of ammonia, ammonia nitrogen can be reacted with o-phthalaldehyde (OPA) and sodium sulfite in an alkaline medium to form a fluorescent compound (λ ex /λ em : 363/426 nm) [7,8]. In our previous research, a homemade mini fluorometer showed high detection sensitivity [9].…”