Development of an automated system for the analysis of inorganic chloramines in swimming pools via multi-syringe chromatography and photometric detection with ABTS

Simultaneous separation and detection of monochloramine, nitrite, and nitrate by step-gradient mixed-mode ion chromatography: Translation from benchtop to portable ion chromatograph

BACKGROUND

Nitrite (NO2-) and nitrate (NO3-) can be produced in the distribution systems of chloraminated drinking water due to the nitrification of ammonia. The most applied inorganic chloramine for this purpose, namely monochloramine (NH2Cl), is also released into aquatic environments from water treatment plants' effluent and within industrial waste streams. Within the treatment process, the continuous monitoring of disinfectant levels is necessary to limit the harmful disinfectant by-product (DBP) formation. Currently, NH2Cl can interfere with nutrient analysis in water samples, and there are no analytical techniques available for the simultaneous analysis of NH2Cl, NO2-, and NO3-.

RESULTS

A green analytical method based on mixed-mode ion chromatography, specifically ion exchange and ion exclusion modes, was developed for the simultaneous separation and detection of NH2Cl, NO2-, and NO3-. The separation was achieved using a Dionex IonPac AG15 column guard column and a step gradient elution involving deionized water and 120.0 mM NaCl. The method was developed using a benchtop HPLC with a custom-made multi-wavelength UV absorbance detector with a 50-mm flow cell to enable the sensitive detection of NH2Cl, NO2-, and NO3- at 240 nm, 220 nm, and 215 nm, respectively. The developed method was then transferred to a portable ion chromatography (IC) system, the Aquamonitrix analyser. The total run time was less than 10 min for both systems. The benchtop HPLC method had a limit of detection (LOD) of 0.07 μg mL-1 as Cl2 for NH2Cl, 0.01 μg mL-1 for NO2-, and 0.03 μg mL-1 for NO3-. The LODs obtained using the portable Aquamonitrix analyser were found to be 0.36 μg mL-1 as Cl2, 0.02 μg mL-1, and 0.11 μg mL-1 for NH2Cl, NO2-, and NO3-, respectively. Excellent linearity (r ≥ 0.9999) was achieved using the portable analyser over the studied concentration ranges. The developed system was applied to the analysis of spiked municipal drinking water samples and showed excellent repeatability for the three analytes at three different concentration levels (RSD of triplicate recovery experiments ≤ 1.9 %). Moreover, the variation in retention time was negligible for the three target analytes with RSD ≤ 0.8 % over 12 runs.

SIGNIFICANCE

We are reporting the first ion chromatographic method for the simultaneous separation and detection of NH2Cl, NO2-, and NO3- in water samples. The monitoring of NH2Cl, NO2-, and NO3- is critical for the determination of disinfectant dosing, water quality, and nitrification status. The developed method can be applied using a benchtop HPLC or via the portable automated IC system to monitor for the three target compounds analysis in water treatment plants.

A Critical Review on Chemical Speciation of Chlorine-Produced Oxidants (CPOs) in Seawater. Part 2: Sampling, Sample Preparation and Non-Chromatographic and Mass Spectrometric-Based Methods

Chlorination of seawater forms a range of secondary oxidative species, collectively termed "chlorine-produced oxidants" (CPOs). These compounds do not have the same biocidal efficacy, the same fate and behavior in the marine environment, the same potential formation of chlorination by-products (CBPs), nor the same effects on marine organisms. Their chemical speciation is an important step toward an accurate assessment of the effectiveness of chlorination and the potential impacts of its releases, among others. The aim of this paper - which is the second of a trilogy dedicated to the chemical speciation of CPOs in seawater - is to cover all aspects related to CPOs analysis in seawater, from sampling to instrumental determination. First, it discusses the procedures involved in synthesis, storage, and standardization of analytical standards. Second, it deals with sampling and sample preparation, addressing all relevant issues related to these two key steps. Third, it provides a comprehensive and up-to-date overview of the colorimetric, titrimetric, and electrochemical methods used for CPOs determination and thoroughly discusses their advantages and limitations. Finally, this review ends with some recommendations for progress in the field of CPO analysis with the three aforementioned approaches. Chromatographic and mass spectrometric-based methods will be covered in the third and final article (Part III).

Effect of ammonia on acute toxicity and disinfection byproducts formation during chlorination of secondary wastewater effluents

Ammonia nitrogen (NH₃-N) significantly affects the occurrence of disinfection byproducts (DBPs) and residual chlorine in chlorinated wastewater, thereby affecting the acute toxicity to aquatic organisms. In this paper, the formation of thirty-five halogenated DBPs and the changes in acute toxicity of luminescent bacteria and zebrafish embryos were evaluated after chlorination of seven secondary wastewater effluents with different NH₃-N concentrations. Results showed that NH₃-N significantly reduced the formation of most DBPs by 82-100%. The acute toxicity was enhanced after chlorination and increased linearly with increasing NH₃-N concentration for luminescent bacteria (r = 0.986, p < 0.05) and zebrafish embryos (r = 0.972, p < 0.05) due to the coexistence of DBPs and monochloramine. According to the toxicity classification system of wastewater, the fitting results indicated that the toxicity level was acceptable for chlorinated wastewater with NH₃-N concentration below 1.00 mg-N/L. DBPs might be the main toxicant to luminescent bacteria in the wastewater with low NH₃-N concentrations (0.06-0.31 mg-N/L), which accounted for 68-97% of the toxicity contribution. By contrast, monochloramine contributed over 80% to the toxicity of luminescent bacteria and zebrafish embryos in the wastewater with high NH₃-N concentrations (2.66-7.17 mg-N/L). Compared to chlorination, chlorine dioxide and ultraviolet disinfection unaffected by NH₃-N could reduce acute toxicity by nearly 100%, primarily due to the lack of residual disinfectant. In view of the high toxicity caused by chlorination, chlorination-dechlorination or chlorine dioxide and UV disinfection are highly recommended for the treatment of wastewater with high NH₃-N concentration.