Selective and trace determination of monochloramine in river water by chemical derivatization and liquid chromatography/tandem mass spectrometry analysis

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).

Haloquinone Chloroimides as Toxic Disinfection Byproducts Identified in Drinking Water

Haloquinone chloroimides (HQCs) are suspected to be highly toxic contaminants, and their production during drinking water disinfection is predicted. However, HQC disinfection byproducts (DBPs) have not been reported in drinking water to date because of analytical limitations. In this study, we developed an analytical method to detect five HQCs, including 2,6-dichloroquinone-4-chloroimide (2,6-DCQC), 2,6-dibromoquinone-4-chloroimide (2,6-DBQC), 2-chloroquinone-4-chloroimide (2-CQC), 3-chloroquinone-4-chloroimide (3-CQC), and 2,6-dichloroquinone-3-methyl-chloroimide (2,6-DCMQC). This method combined a derivatization reaction of HQCs with phenol in alkaline solutions to produce halogenated indophenols, a solid-phase extraction pretreatment using hydrophilic-lipophilic balanced (HLB) cartridges, and a multiple reaction monitoring (MRM) method for quantification. The method was demonstrated to be sensitive and accurate with recoveries of 71-85% and limits of detection of 0.1-0.2 ng/L for the five tested HQCs. Using this method, five tested HQCs were identified in drinking water samples from nine water treatment plants and water distribution systems as new DBPs at concentrations of up to 23.1 ng/L. The cytotoxicity of the five tested HQCs in HepG2 cells was higher than or comparable to that of 2,6-dichloro-1,4-benzoquinone (2,6-DCBQ), an emerging DBP that was hundreds to thousands of times more toxic than regulated DBPs. This study presents the first analytical method for HQC DBPs in drinking water and the first set of occurrence and cytotoxicity data of HQC DBPs.

Challenges and opportunities for on-line monitoring of chlorine-produced oxidants in seawater using portable membrane-introduction Fourier transform-ion cyclotron resonance mass spectrometry

The present study reports the first evaluation of a MIMS device equipped with a high-resolution Fourier transform-ion cyclotron resonance mass spectrometer (FT-ICR MS) for comprehensive speciation of chlorine-produced oxidants (CPO) in seawater. A total of 40 model compounds were studied: 4 inorganic haloamines (mono-, di-, and trichloramine and monobromamine), 22 organic N-haloamines, 12 N-haloamino acids, and 2 free oxidants (HOCl/ClO^- and HOBr/BrO^-). The main key factors influencing the analytes' introduction and their detection were optimized. Under optimized conditions, the rise and fall times of the MIMS signal ranged from 8 to 79 min and from 7 to 73 min, respectively, depending on the compound. Free oxidants and N-haloamino acids, which are ionic or too polar at seawater pH, hardly crossed the membrane, and MIMS analysis was thus unsuitable. Nevertheless, better enrichment and therefore better sensitivity were achieved with organic N-haloamines than with inorganic haloamines. The observed detection limits ranged from tens of μM to sub-μM levels. Oxidant decomposition occurred inside the MIMS device, at a higher rate for N-bromamines than for chlorinated analogues.Graphical abstract.

Is It Possible to Measure Monobromamine Using Colorimetric Methods Based on the Berthelot Reaction, Like for Monochloramine?

Analytical methods based on the Berthelot reaction were recently adapted for determining monochloramine (MCA: NH2Cl) in freshwater. The specificity of the Berthelot reaction with regard to MCA is related to the need for two exchangeable hydrogen atoms to form indophenol blue. MCA can thus be distinguished from organic N-chloramines, which have only one exchangeable hydrogen atom. Monobromamine (MBA: NH2Br) may be formed during chlorination of seawater containing ammonium ions. Quantifying MBA is quite challenging and no method has been reported for its specific determination in seawater. As MBA also has two exchangeable hydrogen atoms, its reactivity might be analogous to that of MCA, but this hypothesis has never been investigated. The aim of this study was to examine the applicability of the so-called “indophenol method” for the determination of the MBA in freshwater and seawater samples. The reaction between MBA and Berthelot reagents was studied in both ultrapure water and artificial seawater. The reaction products were characterized by using gas chromatography coupled to mass spectrometry (GC–MS), Fourier transform-ion cyclotron resonance mass spectrometry (FT–ICR MS), and UV–vis spectroscopy. Results showed that colorimetric methods based on the Berthelot reaction were not suitable for measuring MBA in freshwater or seawater, since NH2Br reacts with alkaline phenol derivative via electrophilic substitution to form ortho- and para-brominated phenols instead of forming indophenol.

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

Inorganic chloramines are disinfection by-products resulting from the unwanted reaction between chlorine used as disinfectant in swimming pools and nitrogenous compounds brought by bathers. This parameter (total chloramines or combined chlorine) is currently measured on site by a colorimetric method that does not allow to measure only inorganic chloramines. In this paper, a multi-syringe chromatography system combined with a post column derivatization is applied for the first time for the specific detection of the three individual inorganic chloramines (monochloramine, dichloramine and trichloramine). These latter ones are separated using a low-pressure monolithic C18 column, and separately detected after a post-column reaction with the chromogenic reagent ABTS (2,2'-azino-bis-(3-ethyl-benzothiazoline)-6-sulfonic acid-diammonium salt). Development of two ABTS reagents provides discrimination of chlorine and monochloramine that are not separated on the column. Optimization of the experimental conditions enables determination of inorganic chloramines with very good detection limits (around 10 μg eq.Cl₂ L^-1) without interferences from other chlorinated compounds such as organic chloramines or free available chlorine. The validation of the whole procedure has been successfully applied to real swimming pools samples.

Tracking Monochloramine Decomposition in MIMS Analysis

Membrane-introduction mass spectrometry (MIMS) has been presented as one of the promising approaches for online and real-time analysis of monochloramine (NH₂Cl) in diverse matrices such as air, human breath, and aqueous matrices. Selective pervaporation of NH₂Cl through the introduction membrane overcomes the need for sample preparation steps. However, both the selectivity and sensitivity of MIMS can be affected by isobaric interferences, as reported by several researchers. High-resolution mass spectrometry helps to overcome those interferences. Recent miniaturization of Fourier transform—ion cyclotron resonance—mass spectrometry (FT-ICR MS) technology coupled to the membrane-introduction system provides a potent tool for in field analysis of monochloramine in environmental matrices. Monochloramine analysis by MIMS based FT-ICR MS system demonstrated decomposition into ammonia. To further clarify the origin of this decomposition, headspace analyses after bypassing the membrane were undertaken and showed that monochloramine decomposition was not exclusively related to interactions within the membrane. Adsorption inside the MIMS device, followed by surface-catalyzed decomposition, was suggested as a plausible additional mechanism of monochloramine decomposition to ammonia.

Determination of monochloramine dissipation kinetics in various surface water qualities under relevant environmental conditions - Consequences regarding environmental risk assessment

A total 190 experiments were performed to study the dissipation kinetics of monochloramine (NH₂Cl, CAS no 10599-90-3) in surface water samples from six rivers (Loire, Rhône, Meuse, Garonne, Seine and Moselle) and an artificial reservoir (Mirgenbach), all located in France. Experiments were conducted in an open reactor, under relevant controlled environmental conditions. The impact of various parameters such as initial NH₂Cl concentration, temperature, pH, presence of sediments, sampling site and collection period was investigated. It was found that NH₂Cl dissipated rapidly without any lag phase, and that decay follows an apparent first-order kinetics (r² > 0.99). Presence of sediment greatly accelerated decay. Half-lives were generally <1 h in river water in presence of natural sediment, but of several hours without sediment. The impact of pH was low for the normal river water pH range. However, increase in temperature significantly accelerated decay. The combination of high initial NH₂Cl concentrations and elevated temperatures generally gives half-lives similar to those obtained at lower temperatures and lower concentrations. Short half-lives (0.06 to 1.50 h) were found in all the surface waters examined, regardless of geographic location of sampling site or collection period, indicating no temporal or site-specific effects on NH₂Cl dissipation. Decay was slightly faster at lower initial concentrations, which supports extrapolation of half-lives measured in this study to a wide range of environmental concentrations. It can thus be assumed that NH₂Cl degradation in river and reservoir waters is mainly determined by presence of sediments and temperature.

A sensitive and specific solid-phase extraction-gas chromatography-tandem mass spectrometry method for the determination of 11 haloacetic acids in aqueous samples

A method for the analysis of 11 haloacetic acids in water samples has been developed. It involves enrichment of the target analytes from water samples by solid-phase extraction, derivatization to methyl esters, and gas chromatography coupled with tandem mass spectrometry determination. Gas chromatography conditions were optimized for a good separation of all haloacetic acids in a short runtime. Data were acquired in the multiple reaction monitoring mode. Six solid-phase extraction sorbents among the most widely used in environmental analysis were tested. Bakerbond SDB was retained because it has been shown to provide the best results for a large class of targeted haloacetic acids. The performances of the developed method have been assessed according to the French Standard NF T 90-210. The calibration curves for all the studied haloacetic acids had consistent slopes with r² values > 0.99. Quantification limits between 0.01 and 0.50 µg l^-1 were achieved. Satisfactory repeatability (relative standard deviation ≤ 14.3%) and intermediate precision (relative standard deviation ≤ 15.7%) were obtained. Applied to the analysis of 15 untreated water samples collected from three rivers, the method allowed the detection of five haloacetic acids including monochloroacetic acid (in 100% of the samples, <0.5-1.85 µg l^-1), dichloroacetic acid (87%, <0.05-0.22 µg l^-1), trichloroacetic acid (93%, <0.05-0.52 µg l^-1), dibromoacetic acid (53%, <0.01-0.40 µg l^-1), tribromoacetic acid (20%, <0.05-0.14 µg l^-1), and bromodichloroacetic acid (6%, < 0.05 µg l^-1).

Formation of 2,6-dichloro-1,4-benzoquinone from aromatic compounds after chlorination

Halobenzoquinones are a group of disinfection byproducts formed by chlorination of certain substances in water. However, to date, the identities of halobenzoquinone precursors remain unknown. In this study, the formation of 2,6-dichloro-1,4-benzoquinone (DCBQ), a typical halobenzoquinone, from 31 aromatic compounds was investigated after 60 min of chlorination. DCBQ was formed from 21 compounds at molar formation yields ranging from 0.0008% to 4.9%. Phenol and chlorinated phenols served as DCBQ precursors, as reported previously. Notably, DCBQ was also formed from para-substituted phenolic compounds. Compounds with alkyl and carboxyl groups as para-substituents led to relatively higher molar formation yields of DCBQ. Moreover, p-quinone-4-chloroimide, 2,6-dichloroquinone-4-chloroimide (2,6-DCQC), and para-substituted aromatic amines (e.g., aniline and N-methyl aniline) served as DCBQ precursors upon chlorination. It was deduced that DCBQ was formed from the para-substituted aromatic amines via 3,5-dichloroquinone-4-chloroimide, a structural isomer of 2,6-DCQC. These results suggested that DCBQ was formed by chlorination of natural organic matter containing para-substituted phenolic species and para-substituted aromatic amines, despite the absence of phenol in water.