In the existence of appropriate amount of disodium ethylenediaminetetraacetate (EDTA), precipitation would not occur in seawater and other natural waters even if the sample solution was adjusted to strong basicity, and the NH3-OPA-sulfite reaction at the optimal pH range could be used to determine ammonium in natural waters. Based on this, a modified o-phthalaldehyde fluorometric analytical method has been established to determine ultratrace ammonium in natural waters. Experimental parameters, including reagent concentration, pH, reaction time, and effect of EDTA, were optimized throughout the experiments based on univariate experimental design. The results showed that the optimal pH range was between 10.80 and 11.70. EDTA did not obviously affect the fluorometric intensity. The linearity range of the proposed method was 0.032–0.500 µmol/L, 0.250–3.00 µmol/L, and 1.00–20.0 µmol/L at the excitation/emission slit of 3 nm/5 nm, 3 nm/3 nm, and 1.5 nm/1.5 nm, respectively. The method detection limit was 0.0099 µmol/L. Compared to the classical OPA method, the proposed method had the advantage of being more sensitive and could quantify ultratrace ammonium without enrichment.

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.

The anaerobic fermentation gas (AFG) with CO2 removed is a sustainable energy resource, and converting CO2 in AFG to value‐added chemicals can kill two birds with one stone. Herein, an ionic porous organic polymer (IPOP‐3) catalyst, with triply synergistic effect of its hydroxide anions, nitrogen activation sites and porous structure, is synthesized. IPOP‐3 exhibits an excellent ability to enrich and convert 50 vol.% CO2 by the reactions with various amines into corresponding formamides. The catalyst is also successfully applied to the N‐formylation of CO2 in AFG, and can be easily recovered and reused. The plausible mechanism for the catalytic N‐formylation is proposed. The hydroxide anion in IPOP‐3 activates the Si−H bond of phenyl silane which reacts with the captured CO2 to form formate anion to facilitate the subsequent conversion into formamide. Our work provides a new idea for the purification of AFG and the resource utilization of CO2.

High performance liquid chromatography (HPLC) was used for the separation and quantification of the low molecular-mass organic acids in the root exudates of Cr-hyperaccumulator Swartz. Eight organic acids, oxalic, tartaric, formic, malic, lactic, acetic, maleic and citric acids, were separated on an XSelect HSS T3 column (250 mm×4.6 mm, 5 μm) within 13 min with the mobile phase of 40 mmol/L potassium dihydrogen phosphate-phosphorous acid at pH 2.40, a flow-rate of 1.0 mL/min, a detection wavelength of 205 nm and a column temperature of 25℃. This is a simple and highly sensitive method for the separation of the eight organic acids with well-shaped peaks. The limits of detection (LODs) for the eight acids ranged from 0.12 mg/L to 12.32 mg/L. Under the optimized conditions, tartaric, malic, lactic, maleic and citric acids in the root exudates were detected with high linearities, acceptable recoveries and excellent precisions. The contents of these acids calculated in the root exudates were (130.90±1.44) μg/g (root dry weight (DW)) for tartaric acid, (1031.34±4.38) μg/g (root DW) for malic acid, (65.54±1.01) μg/g (root DW) for lactic acid, (0.96000±0.00367) μg/g (root DW) for maleic acid and (201.50±1.13) μg/g (root DW) for citric acid. The proposed HPLC method is quite suitable for the simultaneous determination of organic acids in the root exudates of Swartz, and can be used in other plant root exudates as well.

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